[Analysis of pathogenicity and genotype-phenotype correlation of the c.158G>A variant of phenylalanine hydroxylase gene]

OBJECTIVE

To explore the pathogenicity and genotype-phenotype correlation of the c.158G>A variant of phenylalanine hydroxylase (PAH) gene among patients with PAH deficiency.

METHODS

Thirty seven children diagnosed with PAH deficiency at the Obstetrics and Gynecology Hospital Affiliated to Nanjing Medical University between July 2016 and June 2021 were selected as the study subjects. Clinical data and results of genetic testing were retrospectively analyzed.

RESULTS

Among the 37 patients, mild hyperphenylalaninemia (HPA) was observed in 34 cases, two PAH variants (including c.158G>A), which formed a compound heterozygous mutation genotype, were detected in 33 patients, and the remainder one was found to harbor three PAH variants, including homozygous c.158G>A variants and a heterozygous c.842+2T>A variant. Classical phenylketonuria (PKU) was observed in 3 patients, and three PAH variants were detected in each of them, including two with c.[158G>A,842+2T>A]/c.728G>A and c.[158G>A,842+2T>A]/c.611A>G, respectively, and one with c.[158G>A, c.722G>A]/c.728G>A. The c.158G>A variant has a minimal influence on the PAH activity and is associated with a mild HPA phenotype. The variant should thereby be classified as likely benign.

CONCLUSION

When the c.158G>A variant and other pathogenic variants are arranged in cis position, the ultimate phenotype will be determined by the pathogenicity of other variants.

[In vitro expression and functional analyses of the mutants p.R243Q, p.R241C and p.Y356X of the human phenylalanine hydroxylase]

OBJECTIVES

To study the in vitro expression of three phenylalanine hydroxylase (PAH) mutants (p.R243Q, p.R241C, and p.Y356X) and determine their pathogenicity.

METHODS

Bioinformatics techniques were used to predict the impact of PAH mutants on the structure and function of PAH protein. Corresponding mutant plasmids of PAH were constructed and expressed in HEK293T cells. Quantitative reverse transcription polymerase chain reaction was used to measure the mRNA expression levels of the three PAH mutants, and their protein levels were assessed using Western blot and enzyme-linked immunosorbent assay.

RESULTS

Bioinformatics analysis predicted that all three mutants were pathogenic. The mRNA expression levels of the p.R243Q and p.R241C mutants in HEK293T cells were similar to the mRNA expression level of the wild-type control (P>0.05), while the mRNA expression level of the p.Y356X mutant significantly decreased (P<0.05). The PAH protein expression levels of all three mutants were significantly reduced compared to the wild-type control (P<0.05). The extracellular concentration of PAH protein was reduced in the p.R241C and p.Y356X mutants compared to the wild-type control (P<0.05), while there was no significant difference between the p.R243Q mutant and the wild type control (P>0.05).

CONCLUSIONS

p.R243Q, p.R241C and p.Y356X mutants lead to reduced expression levels of PAH protein in eukaryotic cells, with p.R241C and p.Y356X mutants also affecting the function of PAH protein. These three PAH mutants are to be pathogenic.

A base editing strategy using mRNA-LNPs for in vivo correction of the most frequent phenylketonuria variant

The c.1222C>T (p.Arg408Trp) phenylalanine hydroxylase (PAH) variant is the most frequent cause of phenylketonuria (PKU), an autosomal recessive disorder characterized by accumulation of blood phenylalanine (Phe) to neurotoxic levels. Here we devised a therapeutic base editing strategy to correct the variant, using prime-edited hepatocyte cell lines engineered with the c.1222C>T variant to screen a variety of adenine base editors and guide RNAs in vitro, followed by assessment in c.1222C>T humanized mice in vivo. We found that upon delivery of a selected adenine base editor mRNA/guide RNA combination into mice via lipid nanoparticles (LNPs), there was sufficient PAH editing in the liver to fully normalize blood Phe levels within 48 h. This work establishes the viability of a base editing strategy to correct the most common pathogenic variant found in individuals with the most common inborn error of metabolism, albeit with potential limitations compared with other genome editing approaches.

State-of-the-art 2023 on gene therapy for phenylketonuria

Phenylketonuria (PKU) or hyperphenylalaninemia is considered a paradigm for an inherited (metabolic) liver defect and is, based on murine models that replicate all human pathology, an exemplar model for experimental studies on liver gene therapy. Variants in the PAH gene that lead to hyperphenylalaninemia are never fatal (although devastating if untreated), newborn screening has been available for two generations, and dietary treatment has been considered for a long time as therapeutic and satisfactory. However, significant shortcomings of contemporary dietary treatment of PKU remain. A long list of various gene therapeutic experimental approaches using the classical model for human PKU, the homozygous enu2/2 mouse, witnesses the value of this model to develop treatment for a genetic liver defect. The list of experiments for proof of principle includes recombinant viral (AdV, AAV, and LV) and non-viral (naked DNA or LNP-mRNA) vector delivery methods, combined with gene addition, genome, gene or base editing, and gene insertion or replacement. In addition, a list of current and planned clinical trials for PKU gene therapy is included. This review summarizes, compares, and evaluates the various approaches for the sake of scientific understanding and efficacy testing that may eventually pave the way for safe and efficient human application.

Genotypic variants of the tetrahydrobiopterin (BH4) biosynthesis genes in patients with hyperphenylalaninemia from different regions of Iran

BACKGROUND

Hyperphenylalaninemia (HPA) is a metabolic disorder classified into phenylalanine-4-hydroxylase (PAH) and non-PAH deficiency. The latter is produced by mutations in genes involved in the tetrahydrobiopterin (BH4) biosynthesis pathway and DNAJC12 pathogenetic variants. The BH4 metabolism, including de novo biosynthesis involved genes (i.e., guanosine 5'-triphosphate cyclohydrolase I (GTPCH/GCH1), sepiapterin reductase (SR/SPR), 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS)), and two genes that play roles in cofactor regeneration pathway (i.e., dihydropteridine reductase (DHPR/QDPR) and pterin-4α-carbinolamine dehydratase (PCD/PCBD1)). The subsequent systemic hyperphenylalaninemia and monoamine neurotransmitter deficiency lead to neurological consequences. The high rate of consanguineous marriages in Iran substantially increases the incidence of BH4 deficiency.

METHODS

We utilized the Sanger sequencing technique in this study to investigate 14 Iranian patients with non-PAH deficiency. All affected subjects in this study had HPA and no mutation was detected in their PAH gene.

RESULTS

We successfully identified six mutant alleles in BH4-deficiency-associated genes, including three novel mutations: one in QDPR, one in PTS, and one in the PCBD1 gene, thus giving a definite diagnosis to these patients.

CONCLUSION

In this light, appropriate patient management may follow. The clinical effect of reported variants is essential for genetic counseling and prenatal diagnosis in the patients' families and significant for the improvement of precision medicine.

Carriers of autosomal recessive conditions: are they really 'unaffected?'

Mendel's Law of Dominance suggests that recessive disease expression requires the inheritance of two mutated alleles as the dominant, wildtype allele suppresses disease presentation leading to the expression of physiological normal phenotypes. However, there is existing evidence that challenges this school of thought. Here, we summarise existing literature evaluating metabolic and health impacts among carriers of autosomal recessive conditions, focusing on phenylketonuria (PKU), classical homocystinuria, galactosemia and Usher syndrome as examples. Our findings suggest that carriers, often described as 'unaffected', may actually display attenuated symptoms for the recessive disease they are carrying. For instance, PKU is an inborn error of metabolism characterised by the build-up of plasma phenylalanine attributed to the deficiency of the phenylalanine hydroxylase (PAH) enzyme. While less severe, PKU carriers also exhibit this impaired enzymatic activity, leading to elevated plasma phenylalanine levels, especially after phenylalanine consumption. Related to these metabolic alterations in the PAH pathway, there is early evidence to suggest that PKU carriers may have compromised cognitive and mental health outcomes. Overall, research on the health and metabolic impacts of PKU carriers is sparse, with most studies conducted several decades ago. However, early evidence suggests that intermediate phenotypes among carriers of autosomal recessive conditions are plausible. The illustrated possible intermediate phenotypes observed among carriers necessitates future research to determine possible clinical implications among this population.

Analysis of gene variation and long-term follow-up in children with phenylalanine hydroxylase deficiency diagnosed by newborn screening

OBJECTIVES

To retrospectively analyze the variation and characteristics of phenylalanine hydroxylase (PAH) gene, and to observe the long-term treatment effect and follow-up of newborns with PAH deficiency.

METHODS

Clinical data, treatment and follow-up results of 198 patients with PAH deficiency diagnosed by newborn screening in Jinan from 1996 to 2021 were collected. The genetic analysis of 55 patients with PAH deficiency diagnosed by newborn screening in Jinan and 213 patients referred from the surrounding areas of Jinan were summarized. Gene variations were checked by a customized Panel gene detection method. Blood phenylalanine-concentration and physical development indicators including height and weight were regularly monitored. Intellectual development was assessed using a neuropsychological development scale for patients aged 0-6 years and academic performance, and brain injury in patients was assessed using brain magnetic resonance imaging.

RESULTS

c.728G>A, c.158G>A, c.721C>T, c.1068C>A, c.611A>G variations were common in PAH gene. The genotype of c.158G>A variation is compound heterozygous variation, with mainly a mild hyperpheny-lalaninemia. 168 patients with PAH deficiency who were followed-up regularly had normal physical development without dwarfism or malnutrition. Among the 33 preschool patients who underwent mental development assessment, 2 were mentally retarded and the initial treatment age was older than 6 months. Nine patients with an average age of (17.13±2.42) years completed brain magnetic resonance imaging, one case was normal, and 8 cases were abnormal. There were patchy or patchy hyperintense foci near the bilateral lateral ventricles on T2WI, and the intellectual development was normal. Compared with the other eight patients, the blood phenylalanine concentration of the normal child was better and stably controlled within the ideal range.

CONCLUSIONS

c.728G>A, c.158G>A, c.721C>T, c.1068C>A, c.611A>G variations were common in PAH gene. After standardized treatment, most patients with PAH deficiency diagnosed by screening can obtain normal growth and intellectual development in adolescence, but there are different degrees of organic lesions in the cerebral white matter.

Efficient in vivo prime editing corrects the most frequent phenylketonuria variant, associated with high unmet medical need

The c.1222C>T (p.Arg408Trp) variant in the phenylalanine hydroxylase gene (PAH) is the most frequent cause of phenylketonuria (PKU), the most common inborn error of metabolism. This autosomal-recessive disorder is characterized by accumulation of blood phenylalanine (Phe) to neurotoxic levels. Using real-world data, we observed that despite dietary and medical interventions, most PKU individuals harboring at least one c.1222C>T variant experience chronic, severe Phe elevations and do not comply with Phe monitoring guidelines. Motivated by these findings, we generated an edited c.1222C>T hepatocyte cell line and humanized c.1222C>T mouse models, with which we demonstrated efficient in vitro and in vivo correction of the variant with prime editing. Delivery via adeno-associated viral (AAV) vectors reproducibly achieved complete normalization of blood Phe levels in PKU mice, with up to 52% whole-liver corrective PAH editing. These studies validate a strategy involving prime editing as a potential treatment for a large proportion of individuals with PKU.

Predictors of eventual requirement of phenylalanine-restricted diet in young infants with phenylalanine hydroxylase deficiency initially managed with sapropterin monotherapy

BACKGROUND

Phenylalanine (Phe)-restricted diet is associated with lower quality of life for patients with phenylketonuria (PKU), and a concern for caregivers of recently-diagnosed infants. Sapropterin is an oral drug used as an alternative or adjunct to dietary treatment. We have observed that some of the young infants initially managed successfully with sapropterin monotherapy have required dietary treatment in long-term follow-up. We aimed to determine the baseline factors associated with future initiation of dietary treatment in these patients.

METHODS

Data were obtained retrospectively from the medical records of 80 PKU patients started on sapropterin monotherapy before 3 months of age between 2011 and 2021.

RESULTS

The patients were followed for a median of 3.9 years (Q1-Q3: 2.5-5.75 years). Sapropterin was tapered down and discontinued in 5 patients (6.3%) as their Phe levels remained below 360 μmol/L without treatment. Sapropterin monotherapy was sufficient in 62 patients (77.5%), while 13 (16.2%) required dietary treatment. Phe and tyrosine (Tyr) levels, and Phe:Tyr ratios differed significantly among the patients maintained on sapropterin monotherapy and those started on dietary treatment, but the Phe:Tyr ratio at diagnosis was the most important independent baseline variable (OR: 1.61, 95% CI: 1.15-2.27, p = 0.006), with Phe:Tyr ratio at diagnosis >5.25 associated with dietary treatment (sensitivity: 90.0%, specificity: 81.8%). Genotypic phenotype value (GPV), unavailable at baseline, was also associated with dietary treatment (median GPV 9.2 vs. 3.8, p = 0.006), but some genotypes were not specific to the final treatment modality.

DISCUSSION

We propose that the Phe:Tyr ratio at diagnosis is an important indicator to predict dietary requirement in young infants initially managed with sapropterin monotherapy.

Deubiquitinase USP19 enhances phenylalanine hydroxylase protein stability and its enzymatic activity

Phenylalanine hydroxylase (PAH) is the key enzyme in phenylalanine metabolism, deficiency of which is associated with the most common metabolic phenotype of phenylketonuria (PKU) and hyperphenylalaninemia (HPA). A bulk of PKU disease-associated missense mutations in the PAH gene have been studied, and the consequence of each PAH variant vary immensely. Prior research established that PKU-associated variants possess defects in protein folding with reduced cellular stability leading to rapid degradation. However, recent evidence revealed that PAH tetramers exist as a mixture of resting state and activated state whose transition depends upon the phenylalanine concentration and certain PAH variants that fail to modulate the structural equilibrium are associated with PKU disease. Collectively, these findings framed our understanding of the complex genotype-phenotype correlation in PKU. In the current study, we substantiate a link between PAH protein stability and its degradation by the ubiquitin-mediated proteasomal degradation system. Here, we provide an evidence that PAH protein undergoes ubiquitination and proteasomal degradation, which can be reversed by deubiquitinating enzymes (DUBs). We identified USP19 as a novel DUB that regulates PAH protein stability. We found that ectopic expression of USP19 increased PAH protein level, whereas depletion of USP19 promoted PAH protein degradation. Our study indicates that USP19 interacts with PAH and prevents polyubiquitination of PAH subsequently extending the half-life of PAH protein. Finally, the increase in the level of PAH protein by the deubiquitinating activity of USP19 resulted in enhanced metabolic function of PAH. In summary, our study identifies the role of USP19 in regulating PAH protein stability and promotes its metabolic activity. Graphical highlights 1. E3 ligase Cdh1 promotes PAH protein degradation leading to insufficient cellular amount of PAH causing PKU. 2. A balance between E3 ligase and DUB is important to regulate the proteostasis of PAH. 3. USP19 deubiquitinates and stabilizes PAH further protecting it from rapid degradation. 4. USP19 increases the enzymatic activity of PAH, thus maintaining normal Phe levels.

Molecular characterization of phenylketonuria patients from the North Region of Brazil: State of Pará

BACKGROUND

Phenylketonuria (PKU) is an autosomal recessive disease resulting from a deficiency of the enzyme phenylalanine hydroxylase (PAH). Hyperphenylalaninemias (HPA) due to PAH deficiency are accompanied by a wide variety of clinical, biochemical, and molecular features. To identify and characterize pathogenic variants in the PAH gene and establish a correlation between genotype and biochemical phenotype in patients with PKU from state of Pará in the North Region of Brazil.

METHODS

All 13 exons of the PAH gene from 32 patients (21 PKU and 11 non-PKU HPA) were amplified by PCR and submitted to DNA sequencing (Sanger). Biochemical data were obtained from the patients' medical records.

RESULTS

Molecular analysis identified 17 pathogenic variants and 3 nonpathogenic variants. The most frequent pathogenic variants were IVS10-11G>A (7.9%), p. Arg261Gln (7.9%), p. Val388Met (6.3%) and p. Ile65Thr (4.7%). Was observed correlations and inconsistencies between genotype and biochemical phenotype.

CONCLUSION

In PKU patients from state of Pará, North Region of Brazil, a heterogeneous mutation spectrum was revealed, in which the most frequent mutations are variants commonly observed in other Brazilian studies and in the region of the Iberian Peninsula.

Mutational landscape of phenylketonuria in Iran

To date more than 1000 different variants in the PAH gene have been identified in patients with phenylketonuria (PKU). In Iran, several studies have been performed to investigate the genetics bases of the PKU in different parts of the country. In this study, we have analysed and present an update of the mutational landscape of the PAH gene as well as the population genetics and frequencies of detected variants for each cohort. Published articles on PKU mutations in Iran were identified through a comprehensive PubMed, Google Scholar, Web of Science (ISI), SCOPUS, Elsevier, Wiley Online Library and SID literature search using the terms: "phenylketonuria", "hyperphenylalaninemia", and "PKU" in combination with "Iran", "Iranian population", "mutation analysis", and "Molecular genetics". Among the literature-related to genetics of PKU, 18 studies were on the PKU mutations. According to these studies, in different populations of Iran 1497 patients were included for mutation detection that resulted in detection of 129 different mutations. Results of genetic analysis of the different cohorts of Iranian PKU patients show that the most prevalent mutation in Iran is the pathogenic splice variant c.1066-11G > A, occurring in 19.54% of alleles in the cohort. Four other common mutations were p.Arg261Gln, p.Pro281Leu, c.168 + 5G > C and p.Arg243Ter (8.18%, 6.45%, 5.88% and 3.7%, respectively). One notable feature of the studied populations is its high rate of consanguineous marriages. Considering this feature, determining the prevalent PKU mutations could be advantageous for designing screening and diagnostic panels in Iran.

Phenylalanine hydroxylase deficiency treatment and management: A systematic evidence review of the American College of Medical Genetics and Genomics (ACMG)

PURPOSE

Elevated serum phenylalanine (Phe) levels due to biallelic pathogenic variants in phenylalanine hydroxylase (PAH) may cause neurodevelopmental disorders or birth defects from maternal phenylketonuria. New Phe reduction treatments have been approved in the last decade, but uncertainty on the optimal lifespan goal Phe levels for patients with PAH deficiency remains.

METHODS

We searched Medline and Embase for evidence of treatment concerning PAH deficiency up to September 28, 2021. Risk of bias was evaluated based on study design. Random-effects meta-analyses were performed to compare IQ, gestational outcomes, and offspring outcomes based on Phe ≤ 360 μmol/L vs > 360 μmol/L and reported as odds ratio and 95% CI. Remaining results were narratively synthesized.

RESULTS

A total of 350 studies were included. Risk of bias was moderate. Lower Phe was consistently associated with better outcomes. Achieving Phe ≤ 360 μmol/L before conception substantially lowered the risk of negative effect to offspring in pregnant individuals (odds ratio = 0.07, 95% CI = 0.04-0.14; P < .0001). Adverse events due to pharmacologic treatment were common, but medication reduced Phe levels, enabling dietary liberalization.

CONCLUSIONS

Reduction of Phe levels to ≤360 μmol/L through diet or medication represents effective interventions to treat PAH deficiency.

Mutation Characteristics of Phenylalanine Hydroxylase Gene in Children with Phenylketonuria in Yinchuan City

BACKGROUND

Phenylalanine hydroxylase deficiency (PAHD) is an autosomal recessive disorder affecting phenylalanine (Phe) metabolism caused by mutations in the phenylalanine hydroxylase (PAH) gene. It has a complex phenotype with many variants and genotypes in various populations. This study sets out to analyze the screening results of children with phenylketonuria (PKU) in Yinchuan City and characterize the mutation variants of the PAH gene.

METHODS

Phenylketonuria screening results were retrospectively analyzed in 398,605 neonates (207,361 males and 191,244 females) born in different maternity hospitals in Yinchuan City between January 2017 and December 2021. Screening for genetic metabolic diseases was performed with parental consent at their own expense. A comprehensive diagnosis was performed by integrating tandem mass spectrometry (MS/MS) findings with clinical presentations. High-throughput sequencing (HTS) was used to detect genetic and metabolic disease-associated genes in children with PKU who were clinically diagnosed and voluntarily tested. The identified loci were validated through Sanger sequencing and parental verification.

RESULTS

Among the screened newborns, 45 (11.3/100,000) PKU cases were diagnosed. In the 38 cases that underwent self-financed PAH sequencing, 56 mutations were detected in 76 chromosomes, with an overall detection rate of 73.7%. All patients harbored mutant genes, and the 56 mutations detected identified represented 14 variants, including 8 missense mutations, 2 splicing mutations, 2 nonsense mutations, and 2 silent mutations. The mutations were primarily distributed in exons 2, 3, 6, 7, 9, 11, and intron 4, with the highest frequency observed in exon 7 (25 [44.7%]), followed by exon 11 (15 [26.7%]). The most prevalent mutations were exon 7-p.R252W (10 [17.9%]) and exon 7-p.R261Q (8 [14.3%]).

CONCLUSIONS

The PAH gene mutations in children with PKU in Yinchuan City are predominantly concentrated in exons 6, 7, and 11, with the highest detection rates observed for p.R252W and p.R261Q mutations.

Rapid and definitive treatment of phenylketonuria in variant-humanized mice with corrective editing

Phenylketonuria (PKU), an autosomal recessive disorder caused by pathogenic variants in the phenylalanine hydroxylase (PAH) gene, results in the accumulation of blood phenylalanine (Phe) to neurotoxic levels. Current dietary and medical treatments are chronic and reduce, rather than normalize, blood Phe levels. Among the most frequently occurring PAH variants in PKU patients is the P281L (c.842C>T) variant. Using a CRISPR prime-edited hepatocyte cell line and a humanized PKU mouse model, we demonstrate efficient in vitro and in vivo correction of the P281L variant with adenine base editing. With the delivery of ABE8.8 mRNA and either of two guide RNAs in vivo using lipid nanoparticles (LNPs) in humanized PKU mice, we observe complete and durable normalization of blood Phe levels within 48 h of treatment, resulting from corrective PAH editing in the liver. These studies nominate a drug candidate for further development as a definitive treatment for a subset of PKU patients.

Hyperphenylalaninemias genotyping: Results of over 60 years of history in Lombardy, Italy

BACKGROUND

Hyperphenylalaninemias (HPA) are due to several gene mutations, of which the PAH gene is the most frequently involved. Prevalence and incidence of disease vary between populations, with genotype/phenotype correlations not always capable to correctly predict disease severity. The aim of this study was to give an overview of PAH mutations among one of the largest cohort of patients among Europe, born in Lombardy (Italy) starting from late 1970 s and including over a 60 years of activity; furthermore, to evaluate and discuss identified genotype/phenotype correlations and related reliability.

PATIENTS/METHODS

Eight hundred and twenty-six HPA patients in current follow-up at the San Paolo Hospital in Milan (Italy) were retrospectively reviewed, including molecular results and allelic phenotype and genotype values (attributed on the basis of the APV/GPV system) to verify genotype-phenotype correlations.

RESULTS

A total of 166 different PAH variants were reviewed; of those, seven variants were identified as not previously described in literature. Most frequently reported variant was p.Ala403Val, followed by p.Arg261Gln, p.Val245Ala, IVS10-11 g>a, p.Tyr414Cys and p.Leu48Ser. Phenotype prediction, based on APV/GPV, matched the actual phenotype in most cases, but not always.

CONCLUSION/DISCUSSION

The cohort of patients included in this study constitute a representative sample of the HPA population worldwide. Studies on this sample may allow to improve clinical and genetic evaluation performances for affected patients, consequently to develop personalized medicine interventions and provide more precise indications on the correct treatment approach based on the accumulated evidence, also in light of a prognostically reliable but not always conclusive APV/GPV system.

Metabolic phenotyping in phenylketonuria reveals disease clustering independently of metabolic control

Phenylketonuria (PKU, MIM #261600) is one of the most common inborn errors of metabolism (IEM) with an incidence of 1:10000 in the European population. PKU is caused by autosomal recessive mutations in phenylalanine hydroxylase (PAH) and manifests with elevation of phenylalanine (Phe) in plasma and urine. Untreated PKU manifests with intellectual disability including seizures, microcephaly and behavioral abnormalities. Early treatment and good compliance result in a normal intellectual outcome in many but not in all patients. This study examined plasma metabolites in patients with PKU (n = 27), hyperphenylalaninemia (HPA, n = 1) and healthy controls (n = 32) by LC- MS/MS. We hypothesized that PKU patients would exhibit a distinct "submetabolome" compared to that of healthy controls. We further hypothesized that the submetabolome of PKU patients with good metabolic control would resemble that of healthy controls. Results from this study show: (i) Distinct clustering of healthy controls and PKU patients based on polar metabolite profiling, (ii) Increased and decreased concentrations of metabolites within and afar from the Phe pathway in treated patients, and (iii) A specific PKU-submetabolome independently of metabolic control assessed by Phe in plasma. We examined the relationship between PKU metabolic control and extended metabolite profiles in plasma. The PKU submetabolome characterized in this study represents the combined effects of dietary adherence, adjustments in metabolic pathways to compensate for defective Phe processing, as well as metabolic derangements that could not be corrected with dietary management even in patients classified as having good metabolic control. New therapeutic targets may be uncovered to approximate the PKU submetabolome to that of healthy controls and prevent long-term organ damage.

A Comprehensive Study of Disease-Causing Variants in PAH, QDPR, PTS, and PCD Genes in Iranian Patients with Hyperphenylalaninemia: A Systematic Review

BACKGROUND

Hyperphenylalaninemia (HPA) is an autosomal recessive disorder that results from a deficiency in the phenylalanine hydroxylase enzyme (PAH) or from a flaw in the genes that are responsible for the biosynthesis or regeneration of the cofactor tetrahydrobiopterin (BH4), including GCH1, SR, QDPR, PTS, and PCD. Identification of disease-causing variants in these genes can help physicians and clinical geneticists in differential diagnosis, appropriate prescription drugs, and saving time and cost. This study attempted to identify these genes' most prevalent disease-causing variants in Iranian HPA patients.

SUMMARY

This study was performed under the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Before it started, the flow work and inclusion/exclusion criteria were published as a protocol in PROSPERO (CRD42021273705). We conducted a comprehensive search on December 10, 2022, on international online databases, including Web of Science, Scopus, EMBASE, Science Direct, PubMed/Medline, Google Scholar, SID, ISC, and Magiran search engine, to find pertinent publications. Some studies were chosen based on inclusion and exclusion criteria. Altogether, 1,243 Iranian patients from 13 articles were considered. In total, we identified 129 distinct disease-causing variants in PAH (20 novel variants), 29 in QDPR (17 novel variants), 15 in PTS (seven novel variants), and one novel variant in PCD. Twenty disease-causing variants for PAH, 18 for QDPR, and 8 for PTS are included in the genes' proposed genetic diagnostic panels. These panels include more than 75% of the documented disease-causing variants in the Iranian population.

KEY MESSAGES

The findings of this research illustrated the spectrum of disease-causing variants in the PAH, QDPR, PTS, and PCD genes identified in Iranian HPA patients. Common disease-causing variants of these genes may be chosen as a preliminary diagnostic panel for early diagnosis and lowering therapy costs.

Newborn screening and genetic features of patients with hyperphenylalaninemia in a southern Chinese population

BACKGROUND AND AIMS

Hyperphenylalaninemia (HPA) is the most common congenital amino acid metabolism-related defect, but its incidence differs substantially between northern and southern China. We aimed to elucidate the incidence, proportion, and genetic features of HPA in a southern Chinese population.

MATERIALS AND METHODS

We analyzed the HPA screening results for 580,460 newborns from 2014 to 2021.

RESULTS

Of the 296 newborns who tested HPA positive, 56 were diagnosed with HPA, including 47 with phenylalanine hydroxylase deficiency and nine with tetrahydrobiopterin deficiency (BH4D). HPA incidence was estimated to be 1:10,365 newborns. All patients had elevated Phe and Phe/Tyr levels. Thirty-three PAH variants and five PTS variants were detected in HPA patients; 80.6 % PAH variants and 100 % PTS variants were classified as pathogenic or likely pathogenic. In silico tools predicted the remaining variants to be damaging. PAH variants clustered in exons 3, 5, 7, 11, and 12 and PTS variants clustered in exons 2 and 5. The most common PAH variants were c.158G > A (p.R53H, 22.3 %) and c.721C > T (p.R241C, 14.9 %). The most common PTS variants were c.155A > G (p.N52S, 50.0 %) and c.259C > T (p.P87S, 33.3 %).

CONCLUSION

Newborn screening is an effective method for early detection of HPA, but differential diagnosis of BH4D is necessary.

Tetrahydrobiopterin responsiveness in Phenylalanine hydroxylase deficient patients from North-east of Iran: Genotype-phenotype correlation, identification of a novel mutation and 7 new responsive genotypes

Phenylalanine hydroxylase enzyme defects result in a hereditary metabolic disorder called phenylketonuria. Sapropterin (tetrahydrobiopterin) is one of the treatment strategies for this disorder. Even though a correlation between genotype and BH4 responsiveness was established by earlier studies, a subset of mutations often presented inconsistent responses and/or phenotypes. Different genetic background is one of the potential reasons for this fact. In this study, the genotype of a total of 34 PAH deficient patients from Khorasan-Razavi providence in the north-east of Iran was obtained. Among this patients, 21 individuals took the 24 h and 48 h BH4 loading test and if the result was positive, their Phenylalanine tolerance was assessed. It is the first study of its type in patients from Iran to evaluate genotype role in predicting the most probable responsive individuals. The known pathogenic variant p.R169P and the novel variant p. Leu72_Asp75delinsTyr were first classified as responsive.Seven genotypes were reported as responsive for the first time. All patients carrying at least one pathogenic variant, which was previously reported as BH4 responsive, respond to BH4. Three patients with p.L48S, p.R261Q and p.A309V pathogenic variants were exceptions. There was no certain statistical correlation between genotype and response. Genotype and phenotype were significantly correlated and majority of patients with mild phenotype carried at least one non-null pathogenic variant. In Khorasan-Razavi province of Iran, patients with at least one non-null mutation are most probable to demonstrate mild phenotype and respond to BH4 phenotype.

Genetic etiology and clinical challenges of phenylketonuria

This review discusses the epidemiology, pathophysiology, genetic etiology, and management of phenylketonuria (PKU). PKU, an autosomal recessive disease, is an inborn error of phenylalanine (Phe) metabolism caused by pathogenic variants in the phenylalanine hydroxylase (PAH) gene. The prevalence of PKU varies widely among ethnicities and geographic regions, affecting approximately 1 in 24,000 individuals worldwide. Deficiency in the PAH enzyme or, in rare cases, the cofactor tetrahydrobiopterin results in high blood Phe concentrations, causing brain dysfunction. Untreated PKU, also known as PAH deficiency, results in severe and irreversible intellectual disability, epilepsy, behavioral disorders, and clinical features such as acquired microcephaly, seizures, psychological signs, and generalized hypopigmentation of skin (including hair and eyes). Severe phenotypes are classic PKU, and less severe forms of PAH deficiency are moderate PKU, mild PKU, mild hyperphenylalaninaemia (HPA), or benign HPA. Early diagnosis and intervention must start shortly after birth to prevent major cognitive and neurological effects. Dietary treatment, including natural protein restriction and Phe-free supplements, must be used to maintain blood Phe concentrations of 120-360 μmol/L throughout the life span. Additional treatments include the casein glycomacropeptide (GMP), which contains very limited aromatic amino acids and may improve immunological function, and large neutral amino acid (LNAA) supplementation to prevent plasma Phe transport into the brain. The synthetic BH4 analog, sapropterin hydrochloride (i.e., Kuvan®, BioMarin), is another potential treatment that activates residual PAH, thus decreasing Phe concentrations in the blood of PKU patients. Moreover, daily subcutaneous injection of pegylated Phe ammonia-lyase (i.e., pegvaliase; PALYNZIQ®, BioMarin) has promised gene therapy in recent clinical trials, and mRNA approaches are also being studied.

Phenylketonuria oxidative stress and energy dysregulation: Emerging pathophysiological elements provide interventional opportunity

Phenylalanine hydroxylase (PAH) deficient phenylketonuria (PKU) is rightfully considered the paradigm treatable metabolic disease. Dietary substrate restriction (i.e. phenylalanine (Phe) restriction) was applied >60 years ago and remains the primary PKU management means. The traditional model of PKU neuropathophysiology dictates blood Phe over-representation directs asymmetric blood:brain barrier amino acid transport through the LAT1 transporter with subsequent increased cerebral Phe concentration and low concentrations of tyrosine (Tyr), tryptophan (Trp), leucine (Leu), valine (Val), and isoleucine (Ile). Low Tyr and Trp concentrations generate secondary serotonergic and dopaminergic neurotransmitter paucities, widely attributed as drivers of PKU neurologic phenotypes. White matter disease, a central PKU characteristic, is ascribed to Phe-mediated tissue toxicity. Impaired cerebral protein synthesis, by reduced concentrations of non-Phe large neutral amino acids, is another cited pathological mechanism. The PKU amino acid transport model suggests Phe management should be more efficacious than is realized, as even early identified, continuously treated patients that retain therapy compliance into adulthood, demonstrate neurologic disease elements. Reduced cerebral metabolism was an early-recognized element of PKU pathology. Legacy data (late 1960's to mid-1970's) determined the Phe catabolite phenylpyruvate inhibits mitochondrial pyruvate transport. Respirometry of Pah^enu2 cerebral mitochondria have attenuated respiratory chain complex 1 induction in response to pyruvate substrate, indicating reduced energy metabolism. Oxidative stress is intrinsic to PKU and Pah^enu2 brain tissue presents increased reactive oxygen species. Phenylpyruvate inhibits glucose-6-phosphate dehydrogenase that generates reduced niacinamide adenine dinucleotide phosphate the obligatory cofactor of glutathione reductase. Pah^enu2 brain tissue metabolomics identified increased oxidized glutathione and glutathione disulfide. Over-represented glutathione disulfide argues for reduced glutathione reductase activity secondary to reduced NADPH. Herein, we review evidence of energy and oxidative stress involvement in PKU pathology. Data suggests energy deficit and oxidative stress are features of PKU pathophysiology, providing intervention-amenable therapeutic targets to ameliorate disease elements refractory to standard of care.

Spectrum of PAH gene mutations and genotype-phenotype correlation in patients with phenylalanine hydroxylase deficiency from Turkey

OBJECTIVES

The aim of our study was to define the genotype-phenotype correlations of mutations in the PAH gene among the Turkey's Central Anatolian region.

METHODS

Demographic characteristics of 108 patients with hyperphenylalaninemia (HPA) and 94 patients whose diagnosis was confirmed by PAH gene analysis (Sanger DNA Sequence Analysis and Next-Generation Sequencing) were determined retrospectively. Blood phenylalanine levels were analyzed using the high-performance liquid chromatography method.

RESULTS

Mild HPA-not-requiring-treatment (NT) was found in 50.9% of the patients, and a classical phenylketonuria (PKU) phenotype was found in 25.9%. Forty-seven types of variants were identified. The predominant variants were p.Ala403Val (9.9%), p.Ala300Ser (9.4%), and c.1066-11G>A (splicing) (9.4%). Missense mutations accounted for 68% of mutations and attenuated the clinical impact; splice variations were found in 14.8% of cases with severe features. The p.Thr380Met allele was specific to the mild HPA-NT group. The c.1066-11G>A (splicing) allele was associated with classical PKU, whereas the p.Arg408Trp allele was linked to severe symptoms. Three variations of unknown clinical significance were discovered: c.706+4A>T (splicing), c.843-5T>C (splicing), and p.Thr323=. Of these variants, the patient who was homozygous for the c.843-5T>C (splicing) allele related to the classical PKU phenotype. 70% of the patients who underwent tetrahydrobiopterin (BH4) test were responsive. Phenotypes that responded to BH4 treatment were mostly mild phenotypes.

CONCLUSIONS

The PAH genotype is the main factor that determines the phenotype of PKU. Establishing the relationship between the identified genetic mutations and phenotypic characteristics will provide very important data for each patient in terms of the specific management style.

Modeling the cognitive effects of diet discontinuation in adults with phenylketonuria (PKU) using pegvaliase therapy in PAH-deficient mice

Existing phenylalanine hydroxylase (PAH)-deficient mice strains are useful models of untreated or late-treated human phenylketonuria (PKU), as most contemporary therapies can only be initiated after weaning and the pups have already suffered irreversible consequences of chronic hyperphenylalaninemia (HPA) during early brain development. Therefore, we sought to evaluate whether enzyme substitution therapy with pegvaliase initiated near birth and administered repetitively to C57Bl/6-Pah^enu2/enu2 mice would prevent HPA-related behavioral and cognitive deficits and form a model for early-treated PKU. The main results of three reported experiments are: 1) lifelong weekly pegvaliase treatment prevented the cognitive deficits associated with HPA in contrast to persisting deficits in mice treated with pegvaliase only as adults. 2) Cognitive deficits reappear in mice treated with weekly pegvaliase from birth but in which pegvaliase is discontinued at 3 months age. 3) Twice weekly pegvaliase injection also prevented cognitive deficits but again cognitive deficits emerged in early-treated animals following discontinuation of pegvaliase treatment during adulthood, particularly in females. In all studies, pegvaliase treatment was associated with complete correction of brain monoamine neurotransmitter content and with improved overall growth of the mice as measured by body weight. Mean total brain weight however remained low in all PAH deficient mice regardless of treatment. Application of enzyme substitution therapy with pegvaliase, initiated near birth and continued into adulthood, to PAH-deficient Pah^enu2/enu2 mice models contemporary early-treated human PKU. This model will be useful for exploring the differential pathophysiologic effects of HPA at different developmental stages of the murine brain.

Evaluation of patients with phenylalanine metabolism disorder: a single center experience

AIM

The aim is to evaluate the clinical, demographic and laboratory data of the patients we followed up with phenylalanine metabolism disorder.

MATERIALS AND METHODS

In this study, patients with phenylalanine metabolism disorder who applied to Bursa Uludag University Faculty of Medicine, Department of Pediatrics, Pediatric Metabolism Department between 2011 and 2021 were retrospectively examined. The files of 397 patients who were followed up in our pediatric metabolism outpatient clinic and were found to have phenylalanine metabolism disorder by plasma phenylalanine level and molecular genetic analysis were evaluated.

RESULTS

According to the highest plasma phenylalanine levels at admission, mild hyperphenylalaninemia phenotype constituted the largest group of 397 patients with 282 cases (71.1%), while the least common phenotype was malignant phenylketonuria (BH4 metabolism disorder) with four patients (1.0%). The number of patients with classical phenylketonuria was 90 (22.6%). 61 (62.8%) of 97 phenylalanine metabolism disorder cases who underwent BH4 loading test had a response. The mean phenylalanine level of the patients was 3.62 ± 1.31 mg/dL in mild hyperphenylalaninemia, 7.98 ± 3.99 mg/dL in mild phenylketonuria and 11.71 ± 4.39 mg/dL in classical phenylketonuria. While 241 (76%) of 317 patients younger than 8 years old were in the well-controlled group, 76 (24%) were in the poorly-controlled group. While 41 (53.9%) of 76 patients older than 8 years of age were in the well-controlled group, 35 (46.1%) were in the poorly-controlled group.

CONCLUSIONS

In our study, the largest patient group consisted of patients with mild hyperphenylalaninemia, and the least common phenotype was mild phenylketonuria.

Importance of the long non-coding RNA (lncRNA) transcript HULC for the regulation of phenylalanine hydroxylase and treatment of phenylketonuria

More than 1280 variants in the phenylalanine hydroxylase (PAH) gene are responsible for a broad spectrum of phenylketonuria (PKU) phenotypes. While the genotype-phenotype correlation is reaching 88%, for some inconsistent phenotypes with the same genotype additional factors like tetrahydrobiopterin (BH₄), the PAH co-chaperone DNAJC12, phosphorylation of the PAH residues or epigenetic factors may play an important role. Very recently an additional player, the long non-coding RNA (lncRNA) transcript HULC, was described to regulate PAH activity and enhance residual enzyme activity of some PAH variants (e.g., the most common p.R408W) by using HULC mimics. In this review we present an overview of the lncRNA function and in particular the interplay of the HUCL transcript with the PAH and discuss potential applications for the future treatment of some PKU patients.

The effect of casein glycomacropeptide versus free synthetic amino acids for early treatment of phenylketonuria in a mice model

Introduction

Management of phenylketonuria (PKU) is mainly achieved through dietary control with limited intake of phenylalanine (Phe) from food, supplemented with low protein (LP) food and a mixture of free synthetic (FS) amino acids (AA) (FSAA). Casein glycomacropeptide (CGMP) is a natural peptide released in whey during cheese making by the action of the enzyme chymosin. Because CGMP in its pure form does not contain Phe, it is nutritionally suitable as a supplement in the diet for PKU when enriched with specific AAs. Lacprodan^® CGMP-20 (= CGMP) used in this study contained only trace amounts of Phe due to minor presence of other proteins/peptides.

Objective

The aims were to address the following questions in a classical PKU mouse model: Study 1, off diet: Can pure CGMP or CGMP supplemented with Large Neutral Amino Acids (LNAA) as a supplement to normal diet significantly lower the content of Phe in the brain compared to a control group on normal diet, and does supplementation of selected LNAA results in significant lower brain Phe level?. Study 2, on diet: Does a combination of CGMP, essential (non-Phe) EAAs and LP diet, provide similar plasma and brain Phe levels, growth and behavioral skills as a formula which alone consist of FSAA, with a similar composition?.

Material and methods

45 female mice homozygous for the Pah^enu2 mutation were treated for 12 weeks in five different groups; G1(N-CGMP), fed on Normal (N) casein diet (75%) in combination with CGMP (25%); G2 (N-CGMP-LNAA), fed on Normal (N) casein diet (75%) in combination with CGMP (19,7%) and selected LNAA (5,3% Leu, Tyr and Trp); G3 (N), fed on normal casein diet (100%); G4 (CGMP-EAA-LP), fed on CGMP (70,4%) in combination with essential AA (19,6%) and LP diet; G5 (FSAA-LP), fed on FSAA (100%) and LP diet. The following parameters were measured during the treatment period: Plasma AA profiles including Phe and Tyr, growth, food and water intake and number of teeth cut. At the end of the treatment period, a body scan (fat and lean body mass) and a behavioral test (Barnes Maze) were performed. Finally, the brains were examined for content of Phe, Tyr, Trp, dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), serotonin (5-HT) and 5-hydroxyindole-acetic acid (5-HIAA), and the bone density and bone mineral content were determined by dual-energy x-ray absorptiometry.

Results

Study 1: Mice off diet supplemented with CGMP (G1 (N-CGMP)) or supplemented with CGMP in combination with LNAA (G2 (N-CGMP-LNAA)) had significantly lower Phe in plasma and in the brain compared to mice fed only casein (G3 (N)). Extra LNAA (Tyr, Trp and Leu) to CGMP did not have any significant impact on Phe levels in the plasma and brain, but an increase in serotonin was measured in the brain of G2 mice compared to G1. Study 2: PKU mice fed with mixture of CGMP and EAA as supplement to LP diet (G4 (CGMP-EAA-LP)) demonstrated lower plasma-Phe levels but similar brain- Phe levels and growth as mice fed on an almost identical combination of FSAA (G5 (FSAA-LP)).

Conclusion

CGMP can be a relevant supplement for the treatment of PKU.

Frequency of PAH Mutations Among Classic Phenylketon Urea Patients in Mazandaran and Golestan Provinces, North of Iran

BACKGROUND

Phenylketonuria (PKU) is the most common aminoacidopathy with an autosomal recessive inheritance pattern. A global PKU prevalence is estimated about 6.002 in 100,000 newborns. In Iran, the prevalence of PKU is estimated at about 1 in 4,698, and it shows an increasing trend from north (0.0015%) to south (0.02%) of the country. Untreated PKU causes mental retardation, microcephaly, and seizure. PAH gene mutations located at chromosome 12q23 are responsible for the classical type of this disease. The spectrum of PAH mutations is varied in different ethnicities and different parts of the world. The aim of this study was to investigate the frequency of PAH mutation in the Mazandaran province, which could be useful for genetic counseling and prenatal diagnosis.

METHODS

A total of 66 individuals from 33 families from two provinces (9 families from Golestan and 24 families from Mazandaran) from north of Iran participated in this study. After genomic DNA extraction, PAH gene analysis was carried out using DNA sequencing of both coding and non-coding regions by ABI 3130XL genetic analyzer.

RESULTS

Twenty-six different mutations were identified in the PAH gene in this study. Four mutations including IVS10-11 (c.1066-11G>A), c.727C>T (p.Arg243X), c.898G>T (p.Ala300Ser), and c.601C>T (p.His201Tyr) were the most common mutations with 37.48% frequency in Mazandaran province. Most frequent mutations in Golestan province were IVSI0-11 (c.1066-11G>A), c.722delG (p.Arg241fs), c.842C>T (p.Pro281Leu), and IVSII+5 (G>A) with frequency 58.57%.

CONCLUSIONS

The results from the present study verify heterogeneity of the PAH gene and may help to diagnose tests for carrier detection and prenatal diagnosis of the PKU disease in Iranian population.

Gene expression profiles in the brain of phenylketonuria mouse model reversed by the low phenylalanine diet therapy

To gain insight into the potential protective mechanisms of low phenylalanine diet (LPD) in phenylketonuria (PKU), gene expression profiles were studied in the cerebral cortex and hippocampus of a PKU mouse model (BTBR-Pah^enu2). PKU mice were fed with low Phe diet (LPD-PKU group) and normal diet (PKU group). Wild-type mice were treated with normal diet (WT group) as control. After 12 weeks, we detected gene expression in the cerebral cortex and hippocampus of the three groups by RNA-sequencing, and then screened the differentially-expressed genes (DEGs) among the groups by bioinformatics analyses. We found that the transcriptional profiles of both cerebral cortex and hippocampus changed markedly between PKU and WT mice. Furthermore, LPD changed the transcriptional profiles of the cerebral cortex and the hippocampus of PKU mice significantly, especially in the cerebral cortex, with overlaps of genes that changed with the disease and altered by LPD treatment. In the cerebral cortex, hundreds of DEGs enriched in a wide spectrum of biological processes, molecular function, and cellular component, including nervous system development, axon development and guidance, calcium ion binding, modulation of chemical synaptic transmission, and regulation of protein kinase activity. In the hippocampus, the overlapping genes were enriched in positive regulation of long term synaptic, negative regulation of excitatory postsynaptic potential, positive regulation of synapse assembly. Our results showed that genes impaired in PKU and then rescued by LPD might indicate the potential protective capability of LPD in the PKU brain.

Blood phenylalanine reduction reverses gene expression changes observed in a mouse model of phenylketonuria

Phenylketonuria (PKU) is a genetic deficiency of phenylalanine hydroxylase (PAH) in liver resulting in blood phenylalanine (Phe) elevation and neurotoxicity. A pegylated phenylalanine ammonia lyase (PEG-PAL) metabolizing Phe into cinnamic acid was recently approved as treatment for PKU patients. A potentially one-time rAAV-based delivery of PAH gene into liver to convert Phe into tyrosine (Tyr), a normal way of Phe metabolism, has now also entered the clinic. To understand differences between these two Phe lowering strategies, we evaluated PAH and PAL expression in livers of PAHenu2 mice on brain and liver functions. Both lowered brain Phe and increased neurotransmitter levels and corrected animal behavior. However, PAL delivery required dose optimization, did not elevate brain Tyr levels and resulted in an immune response. The effect of hyperphenylalanemia on liver functions in PKU mice was assessed by transcriptome and proteomic analyses. We observed an elevation in Cyp4a10/14 proteins involved in lipid metabolism and upregulation of genes involved in cholesterol biosynthesis. Majority of the gene expression changes were corrected by PAH and PAL delivery though the role of these changes in PKU pathology is currently unclear. Taken together, here we show that blood Phe lowering strategy using PAH or PAL corrects both brain pathology as well as previously unknown lipid metabolism associated pathway changes in liver.

Use of an adeno-associated virus serotype Anc80 to provide durable cure of phenylketonuria in a mouse model

Phenylketonuria (PKU) is the most common inborn error of metabolism of the liver, and results from mutations of both alleles of the phenylalanine hydroxylase gene (PAH). As such, it is a suitable target for gene therapy via gene delivery with a recombinant adeno-associated virus (AAV) vector. Here we use the synthetic AAV vector Anc80 via systemic administration to deliver a functional copy of a codon-optimized human PAH gene, with or without an intron spacer, to the Pah^enu2 mouse model of PKU. Dose-dependent transduction of the liver and expression of PAH mRNA were present with both vectors, resulting in significant and durable reduction of circulating phenylalanine, reaching near control levels in males. Coat color of treated Pah^enu2 mice reflected an increase in pigmentation from brown to the black color of control animals, further indicating functional restoration of phenylalanine metabolism and its byproduct melanin. There were no adverse effects associated with administration of AAV up to 5 × 10¹² VG/kg, the highest dose tested. Only minor and/or transient variations in some liver enzymes were observed in some of the AAV-dosed animals which were not associated with pathology findings in the liver. Finally, there was no impact on cell turnover or apoptosis as evaluated by Ki-67 and TUNEL staining, further supporting the safety of this approach. This study demonstrates the therapeutic potential of AAV Anc80 to safely and durably cure PKU in a mouse model, supporting development for clinical consideration.

An Updated PAH Mutational Spectrum of Phenylketonuria in Mexican Patients Attending a Single Center: Biochemical, Clinical-Genotyping Correlations

Establishing the genotypes of patients with hyperphenylalaninemia (HPA)/phenylketonuria (PKU, MIM#261600) has been considered a cornerstone for rational medical management. However, knowledge of the phenylalanine hydroxylase gene (PAH) mutational spectrum in Latin American populations is still limited. Herein, we aim to update the mutational PAH spectrum in the largest cohort of HPA/PKU Mexican patients (N = 124) reported to date. The biallelic PAH genotype was investigated by Sanger automated sequencing, and genotypes were correlated with documented biochemical phenotypes and theoretical tetrahydrobiopterin (BH₄) responsiveness. Patients were biochemically classified as having classic PKU (50%, 62/124), mild PKU (20.2%, 25/124) and mild HPA (29.8%, 37/124). Furthermore, 78.2% of the included patients (97/124) were identified by newborn screening. A total of 60 different pathogenic variants were identified, including three novel ones (c. 23del, c. 625_626insC and c. 1315 + 5_1315 + 6insGTGTAACAG), the main categories being missense changes (58%, 35/60) and those affecting the catalytic domain (56.6%, 34/60), and c. 60 + 5G > T was the most frequent variant (14.5%, 36/248) mainly restricted (69.2%) to patients from the central and western parts of Mexico. These 60 types of variants constituted 100 different biallelic PAH genotypes, with the predominance of compound-heterozygous ones (96/124, 77%). The expected BH₄ responsiveness based on the PAH genotype was estimated in 52% of patients (65/124), mainly due to the p. (Val388Met) (rs62516101) allele. Instead, our study identified 27 null variants with an allelic phenotype value of zero, with a predominance of c. 60 + 5G > T, which predicts the absence of BH₄ responsiveness. An identical genotype reported in BIOPKUdb was found in 92/124 (74%) of our patients, leading to a genotype–phenotype concordance in 80/92 (86.9%) of them. The high number of variants found confirms the heterogeneous and complex mutational landscape of HPA/PKU in Mexico.

A noncoding RNA modulator potentiates phenylalanine metabolism in mice

The functional role of long noncoding RNAs (lncRNAs) in inherited metabolic disorders, including phenylketonuria (PKU), is unknown. Here, we demonstrate that the mouse lncRNA Pair and human HULC associate with phenylalanine hydroxylase (PAH). Pair-knockout mice exhibited excessive blood phenylalanine (Phe), musty odor, hypopigmentation, growth retardation, and progressive neurological symptoms including seizures, which faithfully models human PKU. HULC depletion led to reduced PAH enzymatic activities in human induced pluripotent stem cell-differentiated hepatocytes. Mechanistically, HULC modulated the enzymatic activities of PAH by facilitating PAH-substrate and PAH-cofactor interactions. To develop a therapeutic strategy for restoring liver lncRNAs, we designed GalNAc-tagged lncRNA mimics that exhibit liver enrichment. Treatment with GalNAc-HULC mimics reduced excessive Phe in Pair -/- and Pah R408W/R408W mice and improved the Phe tolerance of these mice.

DNACJ12 deficiency in patients with unexplained hyperphenylalaninemia: two new patients and a novel variant

In addition to tetrahydrobiopterin deficiencies and phenylalanine hydroxylase deficiency (phenylketonuria) due to PAH variants, the deficiency of the co-chaperone protein DNAJC12 was identified in 2017 as a novel cause of inherited hyperphenylalaninemia, revealing the genetic etiology in previously unresolved cases. In this study, we aimed to investigate DNAJC12 deficiency in non-tetrahydrobiopterin-deficient persistent hyperphenylalaninemia cases without biallelic PAH variants in a single pediatric metabolic center. It was determined retrospectively that 471 patients with non-tetrahydrobiopterin deficiency-hyperphenylalaninemia had undergone PAH gene sequencing and 451 patients had biallelic variants in PAH. DNAJC12 sequencing was performed in the remaining 20 patients, identifying a previously reported homozygous splice-site variant (c.158-2A > T) in one patient with axial hypotonia and developmental delay, and a novel, homozygous c.404del (p.Arg135Lysfs*21) frameshift variant in an asymptomatic patient. In segregation analysis, the asymptomatic patient's both parents were also found to be homozygous for this variant and hyperphenylalaninemic. The parents may have had academic difficulties but intellectual disability could not be confirmed due to lack of cooperation. The symptomatic patient significantly benefited from treatment with sapropterin dihydrochloride and neurotransmitter precursors. DNAJC12 deficiency might be responsible for approximately 10% or more of cases with unexplained hyperphenylalaninemia. The phenotypic spectrum is broad, ranging from early infantile hypotonia to incidental diagnosis in adulthood. Similar to tetrahydrobiopterin deficiencies, early diagnosis and treatment with sapropterin dihydrochloride and neurotransmitter precursors can be beneficial, supporting the analysis of DNACJ12 gene in patients with unexplained hyperphenylalaninemia.

Spectrum of PAH gene mutations in 1547 phenylketonuria patients from Iran: a comprehensive systematic review

As one of the highest prevalence rates in the world, the prevalence of Phenylketonuria (PKU) in Iran has been estimated at 16.5 per 100,000 neonates. The objective of this study was to evaluate the spectrum and frequency of mutations of the phenylalanine hydroxylase (PAH) gene in Iranian PKU patients. A systematic review was carried out on previous studies on PAH gene mutations in Iranian PKU patients. A complete search was carried out on the on-line databases of Scopus, Web of Science, PubMed/Medline, ProQuest, Science Direct, Magiran, SID and the search engine Google Scholar. The keywords of Phenylketonuria, PKU, Phenylalanine Hydroxylase, PAH, and Iran, as well as their Persian equivalents, in all possible combinations were used. Finally, a total of 21 eligible articles with a sample size of 1547 Iranian PKU patients, published between 2003 and 2020, were included in our systematic review. A total of 129 different PAH gene mutations including, IVS10-11G > A (c.1066-11G > A) (19.23%), p.R261Q (c.782G > A) (7.63%), p.P281L (c.842C > T) (6.24%), IVS2 + 5G > C (c.168 + 5G > C) (5.75%), p.R243* (c.727C > T) (3.59%), IVS9 + 5G > A (c.969 + 5G > A) (2.84%), p.R176* (c.526C > T) (2.42%), p.Lys363Nfs*37 (c.1089delG) (2.13%), IVS11 + 1G > C (c.1199 + 1G > C) (2.07%) and p.L48S (c.143 T > C) (2.04%) were identified. The spectrum and frequency of mutations observed in Iran were closer to those observed in the Mediterranean countries. Our results are valuable in planning panel-based studies in provinces with incomplete data on PAH gene mutations. This study is a good reference for genetic counselors and physicians who advise couples in making decisions to maintain or terminate a pregnancy.

In silico screening and molecular dynamics simulation of deleterious PAH mutations responsible for phenylketonuria genetic disorder

Phenylketonuria (PKU) is a genetic disorder that if left untreated can lead to behavioral problems, epilepsy, and even mental retardation. PKU results from mutations within the phenylalanine-4-hydroxylase (PAH) gene that encodes for the PAH protein. The study of all PAH causing mutations is improbable using experimental techniques. In this study, a collection of in silico resources, sorting intolerant from tolerant, Polyphen-2, PhD-SNP, and MutPred were used to identify possible pathogenetic and deleterious PAH non-synonymous single nucleotide polymorphisms (nsSNPs). We identified two variants of PAH, I65N and L311P, to be the most deleterious and disease causing nsSNPs. Molecular dynamics (MD) simulations were carried out to characterize these point mutations on the atomic level. MD simulations revealed increased flexibility and a decrease in the hydrogen bond network for both mutants compared to the native protein. Free energy calculations using the MM/GBSA approach found that BH4 , a drug-based therapy for PKU patients, had a higher binding affinity for I65N and L311P mutants compared to the wildtype protein. We also identify important residues in the BH4 binding pocket that may be of interest for the rational drug design of other PAH drug-based therapies. Lastly, free energy calculations also determined that the I65N mutation may impair the dimerization of the N-terminal regulatory domain of PAH.

Effect of BH4 on blood phenylalanine and tyrosine variations in patients with phenylketonuria

BACKGROUND

In patients with phenylketonuria, stability of blood phenylalanine and tyrosine concentrations might influence brain chemistry and therefore patient outcome. This study prospectively investigated the effects of tetrahydrobiopterin (BH4), as a chaperone of phenylalanine hydroxylase on diurnal and day-to-day variations of blood phenylalanine and tyrosine concentrations.

METHODS

Blood phenylalanine and tyrosine were measured in dried blood spots (DBS) four times daily for 2 days (fasting, before lunch, before dinner, evening) and once daily (fasting) for 6 days in a randomized cross-over design with a period with BH4 and a period without BH4. The sequence was randomized. Eleven proven BH4 responsive PKU patients participated, 5 of them used protein substitutes during BH4 treatment. Natural protein intake and protein substitute dosing was adjusted during the period without BH4 in order to keep DBS phenylalanine levels within target range. Patients filled out a 3-day food diary during both study periods. Variations of DBS phenylalanine and Tyr were expressed in standard deviations (SD) and coefficient of variation (CV).

RESULTS

BH4 treatment did not significantly influence day-to-day phenylalanine and tyrosine variations nor diurnal phenylalanine variations, but decreased diurnal tyrosine variations (median SD 17.6 μmol/l, median CV 21.3%, p = 0.01) compared to diet only (median SD 34.2 μmol/l, median CV 43.2%). Consequently, during BH4 treatment diurnal phenylalanine/tyrosine ratio variation was smaller, while fasting tyrosine levels tended to be higher.

CONCLUSION

BH4 did not impact phenylalanine variation but decreased diurnal tyrosine and phenylalanine/tyrosine ratio variations, possibly explained by less use of protein substitute and increased tyrosine synthesis.

Defining tetrahydrobiopterin responsiveness in phenylketonuria: Survey results from 38 countries

BACKGROUND

A subset of patients with phenylketonuria benefit from treatment with tetrahydrobiopterin (BH4), although there is no consensus on the definition of BH4 responsiveness. The aim of this study therefore was to gain insight into the definitions of long-term BH4 responsiveness being used around the world.

METHODS

We performed a web-based survey targeting healthcare professionals involved in the treatment of PKU patients. Data were analysed according to geographical region (Europe, USA/Canada, other).

RESULTS

We analysed 166 responses. Long-term BH4 responsiveness was commonly defined using natural protein tolerance (95.6%), improvement of metabolic control (73.5%) and increase in quality of life (48.2%). When a specific value for a reduction in phenylalanine concentrations was reported (n = 89), 30% and 20% were most frequently used as cut-off values (76% and 19% of respondents, respectively). When a specific relative increase in natural protein tolerance was used to define long-term BH4 responsiveness (n = 71), respondents most commonly reported cut-off values of 30% and 100% (28% of respondents in both cases). Respondents from USA/Canada (n = 50) generally used less strict cut-off values compared to Europe (n = 96). Furthermore, respondents working within the same center answered differently.

CONCLUSION

The results of this study suggest a very heterogeneous situation on the topic of defining long-term BH4 responsiveness, not only at a worldwide level but also within centers. Developing a strong evidence- and consensus-based definition would improve the quality of BH4 treatment.

Mesenchymal stem cell energy deficit and oxidative stress contribute to osteopenia in the Pahenu2 classical PKU mouse

Osteopenia occurs in a subset of phenylalanine hydroxylase (PAH) deficient phenylketonuria (PKU) patients. While osteopenia is not fully penetrant in patients, the Pah^enu2 classical PKU mouse is universally osteopenic, making it an ideal model of the phenotype. Pah^enu2 Phe management, with a Phe-fee amino acid defined diet, does not improve bone density as histomorphometry metrics remain indistinguishable from untreated animals. Previously, we demonstrated Pah^enu2 mesenchymal stem cells (MSCs) display impaired osteoblast differentiation. Oxidative stress is recognized in PKU patients and PKU animal models. Pah^enu2 MSCs experience oxidative stress determined by intracellular superoxide over-representation. The deleterious impact of oxidative stress on mitochondria is recognized. Oximetry applied to Pah^enu2 MSCs identified mitochondrial stress by increased basal respiration with concurrently reduced maximal respiration and respiratory reserve. Proton leak secondary to mitochondrial complex 1 dysfunction is a recognized superoxide source. Respirometry applied to Pah^enu2 MSCs, in the course of osteoblast differentiation, identified a partial complex 1 deficit. Pah^enu2 MSCs treated with the antioxidant resveratrol demonstrated increased mitochondrial mass by MitoTracker green labeling. In hyperphenylalaninemic conditions, resveratrol increased in situ alkaline phosphatase activity suggesting partial recovery of Pah^enu2 MSCs osteoblast differentiation. Up-regulation of oxidative energy production is required for osteoblasts differentiation. Our data suggests impaired Pah^enu2 MSC developmental competence involves an energy deficit. We posit energy support and oxidative stress reduction will enable Pah^enu2 MSC differentiation in the osteoblast lineage to subsequently increase bone density.

Development of a porcine model of phenylketonuria with a humanized R408W mutation for gene editing

Phenylketonuria (PKU) is a metabolic disorder whereby phenylalanine metabolism is deficient due to allelic variations in the gene for phenylalanine hydroxylase (PAH). There is no cure for PKU other than orthotopic liver transplantation, and the standard of care for patients is limited to dietary restrictions and key amino acid supplementation. Therefore, Pah was edited in pig fibroblasts for the generation of PKU clone piglets that harbor a common and severe human mutation, R408W. Additionally, the proximal region to the mutation was further humanized by introducing 5 single nucleotide polymorphisms (SNPs) to allow for development of gene editing machinery that could be translated directly from the pig model to human PKU patients that harbor at least one classic R408W allele. Resulting piglets were hypopigmented (a single Ossabaw piglet) and had low birthweight (all piglets). The piglets had similar levels of PAH expression, but no detectable enzymatic activity, consistent with the human phenotype. The piglets were fragile and required extensive neonatal care to prevent failure to thrive and early demise. Phenylalanine levels rose sharply when dietary Phe was unrestricted but could be rapidly reduced with a low Phe diet. Fibroblasts isolated from R408W piglets show susceptibility to correction using CRISPR or TALEN, with subsequent homology-directed recombination to correct Pah. This pig model of PKU provides a powerful new tool for development of all classes of therapeutic candidates to treat or cure PKU, as well as unique value for proof-of-concept studies for in vivo human gene editing platforms in the context of this humanized PKU allele.

PREVALENCE OF PAH MUTATIONS IN GEORGIAN PKU PATIENTS COMPARED TO MOST FREQUENT PAH MUTATIONS IN EUROPEAN POPULATIONS

The aim of the study was to compare Georgian PAH mutation spectrum to the most frequent European mutations. Population study publications were reviewed and 20 most frequent European PAH mutations were determined. Mutations were detected in 40 Georgian PKU patients using Sanger sequencing. PAH mutations were detected on all 80 alleles, clinical diagnose of PKU was confirmed in all 40 patients. Detected mutations in Georgian population was: P281L in 37.5%, IVS10-11G>A in 17.5%, R261X in 10%, L48S in 8.75%, E280K in 5%, R270K in 3.75%, E390G in 3.75% and mutations R252W, IVS12+1G>A, R243Q, R261Q, 1089delG, Y387H, EX5del, IVS7-5T>C, IVS12+1G>A, G171R, IVS2+5G>C each in 1.25%. Study revealed that the most common Georgian PAH mutations spectrum differs from the European one. 9 out of 18 detected mutations coincide with the European panel. At the same time more than half (55%) of the mutations found in Georgians were not identified as the most common mutations in Europe. These findings may indicate the necessity for the development of diagnostic panels specific to the Georgian population, including both 9 frequent European PAH mutations and 9 mutations more common for the Georgian population, which will significantly improve the quality of PKU diagnostics in Georgia. The results have been obtained are of an intermediate nature, which propose to continue and complete this research by studying the entire Georgian PKU population.

A novel Pah-exon1 deleted murine model of phenylalanine hydroxylase (PAH) deficiency

Phenylalanine hydroxylase (PAH) deficiency, colloquially known as phenylketonuria (PKU), is among the most common inborn errors of metabolism and in the past decade has become a target for the development of novel therapeutics such as gene therapy. PAH deficient mouse models have been key to new treatment development, but all prior existing models natively express liver PAH polypeptide as inactive or partially active PAH monomers, which complicates the experimental assessment of protein expression following therapeutic gene, mRNA, protein, or cell transfer. The mutant PAH monomers are able to form hetero-tetramers with and inhibit the overall holoenzyme activity of wild type PAH monomers produced from a therapeutic vector. Preclinical therapeutic studies would benefit from a PKU model that completely lacks both PAH activity and protein expression in liver. In this study, we employed CRISPR/Cas9-mediated gene editing in fertilized mouse embryos to generate a novel mouse model that lacks exon 1 of the Pah gene. Mice that are homozygous for the Pah exon 1 deletion are viable, severely hyperphenylalaninemic, accurately replicate phenotypic features of untreated human classical PKU and lack any detectable liver PAH activity or protein. This model of classical PKU is ideal for further development of gene and cell biologics to treat PKU.

The Genetic Landscape and Epidemiology of Phenylketonuria

Phenylketonuria (PKU), caused by variants in the phenylalanine hydroxylase (PAH) gene, is the most common autosomal-recessive Mendelian phenotype of amino acid metabolism. We estimated that globally 0.45 million individuals have PKU, with global prevalence 1:23,930 live births (range 1:4,500 [Italy]-1:125,000 [Japan]). Comparing genotypes and metabolic phenotypes from 16,092 affected subjects revealed differences in disease severity in 51 countries from 17 world regions, with the global phenotype distribution of 62% classic PKU, 22% mild PKU, and 16% mild hyperphenylalaninemia. A gradient in genotype and phenotype distribution exists across Europe, from classic PKU in the east to mild PKU in the southwest and mild hyperphenylalaninemia in the south. The c.1241A>G (p.Tyr414Cys)-associated genotype can be traced from Northern to Western Europe, from Sweden via Norway, to Denmark, to the Netherlands. The frequency of classic PKU increases from Europe (56%) via Middle East (71%) to Australia (80%). Of 758 PAH variants, c.1222C>T (p.Arg408Trp) (22.2%), c.1066-11G>A (IVS10-11G>A) (6.4%), and c.782G>A (p.Arg261Gln) (5.5%) were most common and responsible for two prevalent genotypes: p.[Arg408Trp];[Arg408Trp] (11.4%) and c.[1066-11G>A];[1066-11G>A] (2.6%). Most genotypes (73%) were compound heterozygous, 27% were homozygous, and 55% of 3,659 different genotypes occurred in only a single individual. PAH variants were scored using an allelic phenotype value and correlated with pre-treatment blood phenylalanine concentrations (n = 6,115) and tetrahydrobiopterin loading test results (n = 4,381), enabling prediction of both a genotype-based phenotype (88%) and tetrahydrobiopterin responsiveness (83%). This study shows that large genotype databases enable accurate phenotype prediction, allowing appropriate targeting of therapies to optimize clinical outcome.

[Screening of phenylketonuria and analysis of phenylalanine hydroxylase gene in 380 996 newborns from Hainan province]

Objective: To investigate the incidence of phenylketonuria and distribution characteristics of phenylalanine hydroxylase (PAH) gene in newborns from Hainan province. Methods: Dry blood spot specimens of heels from 380 996 newborns in Hainan province from January 2017 to December 2019 were collected. Phenylalanine (Phe) concentrations in these dry blood spots were measured by the fluorescence method to screen phenylketonuria (PKU). A second dry blood spot sample will be collected if suspicious samples were detected after initial screening. Tandem mass spectrometry were used to detect the concentrations of Phe and tyrosine. Urine samples of the suspected newborns were sent out for urotrexate spectrum analysis and tetrahydrobiopterin loading test. PCR and flow-through rapid hybridization method were employed to detect PAH gene mutations. Meanwhile, peripheral blood samples of suspicious newborns of PKU and their parents were collected to perform gene sequencing. Results: Among the 380 996 newborns, 39 were suspected and 14 were diagnosed with PKU, including 11 cases of PAH deficiency and 3 cases of tetrahydrobiopterin deficiency. Of 14 confirmed cases, there were 8 male cases and 6 female cases. In the newborn population of Hainan province, the annual incidence of PKU was 1.22/100 000. Thirteen PAH gene mutations were detected in confirmed cases: c.728G>A, c.158G>A, c.1238G>C, c.611A>G, c.1068C>A, c.706+5G>A, c.740G>T, c.1081A>T, c.793T>G, c.1223G>A, c.721C>T, c.331C>T and c.1174T>A. Conclusions: PKU has a high incidence in newborn population of Hainan province in the past three years. The PAH gene has a wide spectrum of mutations. Two rare mutations were also found: c.793T>G and c.706+5G>A.

Maternal PKU: Defining phenylalanine tolerance and its variation during pregnancy, according to genetic background

BACKGROUND AND AIMS

Phenylketonuria (PKU)-affected women may become pregnant, and dietary phenylalanine (Phe) intake must be adjusted according to Phe tolerance. We report our experience with maternal PKU in relation to genotype PKU heterogeneity.

METHODS AND RESULTS

A total of 10 pregnancies in 7 PKU women (7 different genotypes) were followed up as part of personalized care. Phe tolerance during preconception and pregnancy was assessed by strict dietary control and weekly Phe measurement (blood spots) in relation to genotype. Most women had stopped PKU diet during childhood or adolescence and six pregnancies were unplanned; a phenylalanine-restricted diet was reinstituted soon after conception. Women were classified according to their Phe levels at birth screening and genotype. Phe tolerance increased systematically in the course of pregnancy in all cases, but the increase was different in subjects with classic PKU (cPKU) when compared with cases with mild hyperphenylalaninemia (mHPA), both on average (+297 mg/day in cPKU vs. 597 in mHPA; P = 0.017) and as percentage (+107% in cPKU vs. +17% in mHPA). Notably, Phe tolerance also varied in the same women in the course of different pregnancies, when body weight gain was also different. Two newborns from the same cPKU mother (unplanned pregnancies on free diet) were affected by congenital alterations.

CONCLUSIONS

Several factors influence metabolic phenotype in maternal PKU, to an unpredictable extent even in the same woman. The number of maternal PKU cases is growing in dedicated Nutrition Units, and the burden associated with careful management of this condition for the health care system should be adequately considered.

Molecular characterization of precise in vivo targeted gene integration in human cells using AAVHSC15

Targeted gene integration via precise homologous recombination (HR)-based gene editing has the potential to correct genetic diseases. AAV (adeno-associated virus) can mediate nuclease-free gene integration at a disease-causing locus. Therapeutic application of AAV gene integration requires quantitative molecular characterization of the edited sequence that overcome technical obstacles such as excess episomal vector genomes and lengthy homology arms. Here we describe a novel molecular methodology that utilizes quantitative next-generation sequencing to characterize AAV-mediated targeted insertion and detects the presence of unintended mutations. The methods described here quantify targeted insertion and query the entirety of the target locus for the presence of insertions, deletions, single nucleotide variants (SNVs) and integration of viral components such as inverted terminal repeats (ITR). Using a humanized liver murine model, we demonstrate that hematopoietic stem-cell derived AAVHSC15 mediates in vivo targeted gene integration into human chromosome 12 at the PAH (phenylalanine hydroxylase) locus at 6% frequency, with no sign of co-incident random mutations at or above a lower limit of detection of 0.5% and no ITR sequences at the integration sites. Furthermore, analysis of heterozygous variants across the targeted locus using the methods described shows a pattern of strand cross-over, supportive of an HR mechanism of gene integration with similar efficiencies across two different haplotypes. Rapid advances in the application of AAV-mediated nuclease-free target integration, or gene editing, as a new therapeutic modality requires precise understanding of the efficiency and the nature of the changes being introduced to the target genome at the molecular level. This work provides a framework to be applied to homologous recombination gene editing platforms for assessment of introduced and natural sequence variation across a target site.

Long noncoding RNA PAHAL modulates locust behavioural plasticity through the feedback regulation of dopamine biosynthesis

Some long noncoding RNAs (lncRNAs) are specifically expressed in brain cells, implying their neural and behavioural functions. However, how lncRNAs contribute to neural regulatory networks governing the precise behaviour of animals is less explored. Here, we report the regulatory mechanism of the nuclear-enriched lncRNA PAHAL for dopamine biosynthesis and behavioural adjustment in migratory locusts (Locusta migratoria), a species with extreme behavioral plasticity. PAHAL is transcribed from the sense (coding) strand of the gene encoding phenylalanine hydroxylase (PAH), which is responsible for the synthesis of dopamine from phenylalanine. PAHAL positively regulates PAH expression resulting in dopamine production in the brain. In addition, PAHAL modulates locust behavioral aggregation in a population density-dependent manner. Mechanistically, PAHAL mediates PAH transcriptional activation by recruiting serine/arginine-rich splicing factor 2 (SRSF2), a transcription/splicing factor, to the PAH proximal promoter. The co-activation effect of PAHAL requires the interaction of the PAHAL/SRSF2 complex with the promoter-associated nascent RNA of PAH. Thus, the data support a model of feedback modulation of animal behavioural plasticity by an lncRNA. In this model, the lncRNA mediates neurotransmitter metabolism through orchestrating a local transcriptional loop.

The neurotransmitter dopamine is crucial for the neuronal and behavioral response in animals. Phenylalanine hydroxylase (PAH) is involved in dopamine biosynthesis and behavioral regulation in the migratory locust. However, the molecular mechanism for the fine tuning of PAH expression in behavioral response remains ambiguous. Here we discovered a nuclear-enriched lncRNA PAHAL that is transcribed from the coding strand of the PAH gene in the locust (i.e., sense lncRNA). PAHAL positively regulated PAH expression and dopamine production in the brain. In addition, PAHAL modulated behavioral aggregation of the locust. Mechanistically, PAHAL mediated the transcriptional activation of PAH by recruiting SRSF2, a transcription/splicing factor, to the promoter-associated nascent RNA of PAH. These data support a model of feedback modulation of dopamine biosynthesis and behavioral plasticity via a sense lncRNA in the catecholamine metabolic pathway.

Metabolomics analysis reveals perturbations of cerebrocortical metabolic pathways in the Pahenu2 mouse model of phenylketonuria

AIMS

Phenylketonuria (PKU), which is caused by mutations in the phenylalanine hydroxylase (PAH) gene, is one of the most common inherited diseases of amino acid metabolism. Phenylketonuria is characterized by an abnormal accumulation of phenylalanine and its metabolites in body fluids and brain tissues, subsequently leading to severe brain dysfunction. Various pathophysiological and molecular mechanisms underlying brain dysfunction in PKU have been described. However, the metabolic changes and their impacts on the function of cerebral cortices of patients with PKU remain largely unknown.

METHODS

We measured the levels of small molecule metabolites in the cerebrocortical tissues of PKU mice and wild-type control mice using liquid chromatography-mass spectrometry (LC-MS)-based metabolome analysis. Differential metabolites were further subjected to metabolic pathway and enrichment analysis.

RESULTS

Metabolome analysis revealed 35 compounds among 143 detected metabolites were significantly changed in PKU mice as compared to those in their wild-type littermates. Metabolic pathway and enrichment analysis of these differential metabolites showed that multiple metabolic pathways, including phenylalanine, tyrosine, and tryptophan biosynthesis; valine, leucine, and isoleucine biosynthesis; alanine, aspartate, and glutamate metabolism; purine metabolism; arginine and proline metabolism and methionine metabolism, were impacted in the cerebral cortices of PKU mice.

CONCLUSIONS

The data revealed that multiple metabolic pathways in cerebral cortices of PKU mice were disturbed, suggesting that the disturbances of the metabolic pathways might contribute to neurological or neurodevelopmental dysfunction in PKU, which could thus provide new insights into brain pathogenic mechanisms in PKU as well as mechanistic insights for better understanding the complexity of the metabolic mechanisms of the brain dysfunction in PKU.

Directed Metabolic Pathway Evolution Enables Functional Pterin-Dependent Aromatic-Amino-Acid Hydroxylation in Escherichia coli

Tetrahydrobiopterin-dependent hydroxylation of aromatic amino acids is the first step in the biosynthesis of many neuroactive compounds in humans. A fundamental challenge in building these pathways in Escherichia coli is the provision of the non-native hydroxylase cofactor, tetrahydrobiopterin. To solve this, we designed a genetic selection that relies on the tyrosine synthesis activity of phenylalanine hydroxylase. Using adaptive laboratory evolution, we demonstrate the use of this selection to discover: (1) a minimum set of heterologous enzymes and a host folE (T198I) mutation for achieving this type of hydroxylation chemistry in whole cells, (2) functional complementation of tetrahydrobiopterin by indigenous cofactors, and (3) a tryptophan hydroxylase mutation for improving protein abundance. Thus, the goal of having functional aromatic-amino-acid hydroxylation in E. coli was achieved through directed metabolic pathway evolution.