Clinical and biochemical footprints of congenital disorders of glycosylation: Proposed nosology

We have identified 200 congenital disorders of glycosylation (CDG) caused by 189 different gene defects and have proposed a classification system for CDG based on the mode of action. This classification includes 8 categories: 1. Disorders of monosaccharide synthesis and interconversion, 2. Disorders of nucleotide sugar synthesis and transport, 3. Disorders of N-linked protein glycosylation, 4. Disorders of O-linked protein glycosylation, 5. Disorders of lipid glycosylation, 6. Disorders of vesicular trafficking, 7. Disorders of multiple glycosylation pathways and 8. Disorders of glycoprotein/glycan degradation. Additionally, using information from IEMbase, we have described the clinical involvement of 19 organs and systems, as well as essential laboratory investigations for each type of CDG. Neurological, dysmorphic, skeletal, and ocular manifestations were the most prevalent, occurring in 81%, 56%, 53%, and 46% of CDG, respectively. This was followed by digestive, cardiovascular, dermatological, endocrine, and hematological symptoms (17-34%). Immunological, genitourinary, respiratory, psychiatric, and renal symptoms were less frequently reported (8-12%), with hair and dental abnormalities present in only 4-7% of CDG. The information provided in this study, including our proposed classification system for CDG, may be beneficial for healthcare providers caring for individuals with metabolic conditions associated with CDG.

Does hyperphenylalaninemia induce brain glucose hypometabolism? Cerebral spinal fluid findings in treated adult phenylketonuric patients

Despite numerous studies in human patients and animal models for phenylketonuria (PKU; OMIM#261600), the pathophysiology of PKU and the underlying causes of brain dysfunction and cognitive problems in PKU patients are not well understood. In this study, lumbar cerebral spinal fluid (CSF) was obtained immediately after blood sampling from early-treated adult PKU patients who had fasted overnight. Metabolite and amino acid concentrations in the CSF of PKU patients were compared with those of non-PKU controls. The CSF concentrations and CSF/plasma ratios for glucose and lactate were found to be below normal, similar to what has been reported for glucose transporter1 (GLUT1) deficiency patients who exhibit many of the same clinical symptoms as untreated PKU patients. CSF glucose and lactate levels were negatively correlated with CSF phenylalanine (Phe), while CSF glutamine and glutamate levels were positively correlated with CSF Phe levels. Plasma glucose levels were negatively correlated with plasma Phe concentrations in PKU subjects, which partly explains the reduced CSF glucose concentrations. Although brain glucose concentrations are unlikely to be low enough to impair brain glucose utilization, it is possible that the metabolism of Phe in the brain to produce phenyllactate, which can be transported across the blood-brain barrier to the blood, may consume glucose and/or lactate to generate the carbon backbone for glutamate. This glutamate is then converted to glutamine and carries the Phe-derived ammonia from the brain to the blood. While this mechanism remains to be tested, it may explain the correlations of CSF glutamine, glucose, and lactate concentrations with CSF Phe.

Consensus guidelines for the diagnosis and management of succinic semialdehyde dehydrogenase deficiency

Succinic semialdehyde dehydrogenase deficiency (SSADHD) (OMIM #271980) is a rare autosomal recessive metabolic disorder caused by pathogenic variants of ALDH5A1. Deficiency of SSADH results in accumulation of γ-aminobutyric acid (GABA) and other GABA-related metabolites. The clinical phenotype of SSADHD includes a broad spectrum of non-pathognomonic symptoms such as cognitive disabilities, communication and language deficits, movement disorders, epilepsy, sleep disturbances, attention problems, anxiety, and obsessive-compulsive traits. Current treatment options for SSADHD remain supportive, but there are ongoing attempts to develop targeted genetic therapies. This study aimed to create consensus guidelines for the diagnosis and management of SSADHD. Thirty relevant statements were initially addressed by a systematic literature review, resulting in different evidence levels of strength according to the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) criteria. The highest level of evidence (level A), based on randomized controlled trials, was unavailable for any of the statements. Based on cohort studies, Level B evidence was available for 12 (40%) of the statements. Thereupon, through a process following the Delphi Method and directed by the Appraisal of Guidelines for Research and Evaluation (AGREE II) criteria, expert opinion was sought, and members of an SSADHD Consensus Group evaluated all the statements. The group consisted of neurologists, epileptologists, neuropsychologists, neurophysiologists, metabolic disease specialists, clinical and biochemical geneticists, and laboratory scientists affiliated with 19 institutions from 11 countries who have clinical experience with SSADHD patients and have studied the disorder. Representatives from parent groups were also included in the Consensus Group. An analysis of the survey's results yielded 25 (83%) strong and 5 (17%) weak agreement strengths. These first-of-their-kind consensus guidelines intend to consolidate and unify the optimal care that can be provided to individuals with SSADHD.

CYP2U1: An emerging treatable neurometabolic disease with cerebral folate deficiency in 2 Chinese brothers

With the rapid advancement of medical technologies in genomic and molecular medicine, the number of treatable neurometabolic diseases is quickly expanding. Spastic paraplegia 56 (SPG56), one of the severe autosomal recessive forms of neurodegenerative disorders caused by pathogenic variants in the CYP2U1 gene, has no reported specific targeted treatment yet. Here we report 2 Chinese brothers with CYP2U1 bi-allelic pathogenic variants with cerebral folate deficiency who were treated for over a decade with folinic acid supplement. Patients have remained stable under therapy.

Clinical and biochemical footprints of inherited metabolic disease. XVI. Hematological abnormalities

Many classical inherited metabolic diseases (IMDs) are associated with significant hematological complications such as anemia or thrombosis. While these may not be the prominent presenting feature of these conditions, management of these issues is important for optimal outcomes in people with IMDs. Some disorders that are included in the nosology of inherited metabolic disorders, such as inherited disorders of red cell energy metabolism, have purely hematological features, and have typically been cared for by a hematologist. In the 16th issue of the Footprints series, we identified 265 IMDs associated with hematological abnormalities. We review the major hematological manifestations of IMDs, suggest further investigation of hematological findings, and discuss treatment options available for specific hematological complications of IMDs.

Clinical and biochemical footprints of inherited metabolic diseases. XIV. Metabolic kidney diseases

Kidney disease is a global health burden with high morbidity and mortality. Causes of kidney disease are numerous, extending from common disease groups like diabetes and arterial hypertension to rare conditions including inherited metabolic diseases (IMDs). Given its unique anatomy and function, the kidney is a target organ in about 10% of known IMDs, emphasizing the relevant contribution of IMDs to kidney disease. The pattern of injury affects all segments of the nephron including glomerular disease, proximal and distal tubular damage, kidney cyst formation, built-up of nephrocalcinosis and stones as well as severe malformations. We revised and updated the list of known metabolic etiologies associated with kidney involvement and found 190 relevant IMDs. This represents the 14th of a series of educational articles providing a comprehensive and revised list of metabolic differential diagnoses according to system involvement.

Clinical and biochemical footprints of inherited metabolic diseases. XIII. Respiratory manifestations

At any age, respiratory manifestations are a major cause of increased morbidity and mortality of inherited metabolic diseases (IMDs). Type and severity are extremely variable, this depending on the type of the underlying disorder. Symptoms and signs originating from upper or lower airways and/or thoracic wall and/or respiratory muscles involvement can occur either at presentation or in the late clinical course. Acute respiratory symptoms can trigger metabolic decompensation which, in turn, makes airway symptoms worse, creating a vicious circle. We have identified 181 IMDs associated with various types of respiratory symptoms which were classified into seven groups according to the type of clinical manifestations affecting the respiratory system: (i) respiratory failure, (ii) restrictive lung disease, (iii) interstitial lung disease, (iv) lower airway disease, (v) upper airway obstruction, (vi) apnea, and (vii) other. We also provided a list of investigations to be performed based on the respiratory phenotypes and indicated the therapeutic strategies currently available for IMD-associated airway disease. This represents the thirteenth issue in a series of educational summaries providing a comprehensive and updated list of metabolic differential diagnoses according to system involvement.

Clinical and biochemical footprints of inherited metabolic diseases. XV. Epilepsies

We provide a comprehensive overview of inherited metabolic disorders (IMDs) in which epilepsy is a prominent manifestation. Our unique database search has identified 256 IMDs associated with various types of epilepsies, which we classified according to the classic pathophysiology-based classification of IMDs, and according to selected seizure-related factors (neonatal seizures, infantile spasms, myoclonic seizures, and characteristic EEG patterns) and treatability for the underlying metabolic defect. Our findings indicate that inherited metabolic epilepsies are more likely to present in the neonatal period, with infantile spasms or myoclonic seizures. Additionally, the ∼20% of treatable inherited metabolic epilepsies found by our search were mainly associated with the IMD groups of "cofactor and mineral metabolism" and "Intermediary nutrient metabolism." The information provided by this study, including a comprehensive list of IMDs with epilepsy stratified according to age of onset, and seizure type and characteristics, along with an overview of the key clinical features and proposed diagnostic and therapeutic approaches, may benefit any epileptologist and healthcare provider caring for individuals with metabolic conditions.

Prevalence of DDC genotypes in patients with aromatic L-amino acid decarboxylase (AADC) deficiency and in silico prediction of structural protein changes

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare autosomal recessive genetic disorder affecting the biosynthesis of dopamine, a precursor of both norepinephrine and epinephrine, and serotonin. Diagnosis is based on the analysis of CSF or plasma metabolites, AADC activity in plasma and genetic testing for variants in the DDC gene. The exact prevalence of AADC deficiency, the number of patients, and the variant and genotype prevalence are not known. Here, we present the DDC variant (n = 143) and genotype (n = 151) prevalence of 348 patients with AADC deficiency, 121 of whom were previously not reported. In addition, we report 26 new DDC variants, classify them according to the ACMG/AMP/ACGS recommendations for pathogenicity and score them based on the predicted structural effect. The splice variant c.714+4A>T, with a founder effect in Taiwan and China, was the most common variant (allele frequency = 32.4%), and c.[714+4A>T];[714+4A>T] was the most common genotype (genotype frequency = 21.3%). Approximately 90% of genotypes had variants classified as pathogenic or likely pathogenic, while 7% had one VUS allele and 3% had two VUS alleles. Only one benign variant was reported. Homozygous and compound heterozygous genotypes were interpreted in terms of AADC protein and categorized as: i) devoid of full-length AADC, ii) bearing one type of AADC homodimeric variant or iii) producing an AADC protein population composed of two homodimeric and one heterodimeric variant. Based on structural features, a score was attributed for all homodimers, and a tentative prediction was advanced for the heterodimer. Almost all AADC protein variants were pathogenic or likely pathogenic.

Clinical and biochemical footprints of inherited metabolic diseases. XII. Immunological defects

Immunological problems are increasingly acknowledged manifestations in many inherited metabolic diseases (IMDs), ranging from exaggerated inflammation, autoimmunity and abnormal cell counts to recurrent microbial infections. A subgroup of IMDs, the congenital disorders of glycosylation (CDG), includes CDG types that are even classified as primary immunodeficiencies. Here, we reviewed the list of metabolic disorders reported to be associated with various immunological defects and identified 171 IMDs accompanied by immunological manifestations. Most IMDs are accompanied by immune dysfunctions of which immunodeficiency and infections, innate immune defects, and autoimmunity are the most common abnormalities reported in 144/171 (84%), 44/171 (26%) and 33/171 (19%) of IMDs with immune system involvement, respectively, followed by autoinflammation 17/171 (10%). This article belongs to a series aiming at creating and maintaining a comprehensive list of clinical and metabolic differential diagnoses according to organ system involvement.

Clinical and biochemical footprints of inherited metabolic disorders. XI. Gastrointestinal symptoms

Inherited metabolic disorders presenting with gastrointestinal (GI) symptoms are characterized by the dysfunction of the esophagus, stomach, small and large intestines, and pancreas. We have summarized associations of signs and symptoms in 339 inherited metabolic diseases presenting with GI symptoms. Feeding difficulties represent the most common abnormality reported for IMDs with GI involvement (37%) followed by intestinal problems (30%), vomiting (22%), stomach and pancreas involvement (8% each), and esophagus involvement (4%). This represents the eleventh of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Spectrum of DDC variants causing aromatic l-amino acid decarboxylase (AADC) deficiency and pathogenicity interpretation using ACMG-AMP/ACGS recommendations

Pathogenic variants in dopa decarboxylase (DDC), the gene encoding the aromatic l-amino acid decarboxylase (AADC) enzyme, lead to a severe deficiency of neurotransmitters, resulting in neurological, neuromuscular, and behavioral manifestations clinically characterized by developmental delays, oculogyric crises, dystonia, and severe neurologic dysfunction in infancy. Historically, therapy has been aimed at compensating for neurotransmitter abnormalities, but response to pharmacologic therapy varies, and in most cases, the therapy shows little or no benefit. A novel human DDC gene therapy was recently approved in the European Union that targets the underlying genetic cause of the disorder, providing a new treatment option for patients with AADC deficiency. However, the applicability of human DDC gene therapy depends on the ability of laboratories and clinicians to interpret the results of genetic testing accurately enough to diagnose the patient. An accurate interpretation of genetic variants depends in turn on expert-guided curation of locus-specific databases. The purpose of this research was to identify previously uncharacterized DDC variants that are of pathologic significance in AADC deficiency as well as characterize and curate variants of unknown significance (VUSs) to further advance the diagnostic accuracy of genetic testing for this condition. DDC variants were identified using existing databases and the literature. The pathogenicity of the variants was classified using modified American College of Medical Genetics and Genomics/Association for Molecular Pathology/Association for Clinical Genomic Science (ACMG-AMP/ACGS) criteria. To improve the current variant interpretation recommendations, in silico variant interpretation tools were combined with structural 3D modeling of protein variants and applied comparative analysis to predict the impact of the variant on protein function. A total of 422 variants were identified (http://biopku.org/home/pnddb.asp). Variants were identified on nearly all introns and exons of the DDC gene, as well as the 3' and 5' untranslated regions. The largest percentage of the identified variants (48%) were classified as missense variants. The molecular effects of these missense variants were then predicted, and the pathogenicity of each was classified using a number of variant effect predictors. Using ACMG-AMP/ACGS criteria, 7% of variants were classified as pathogenic, 32% as likely pathogenic, 58% as VUSs of varying subclassifications, 1% as likely benign, and 1% as benign. For 101 out of 108 reported genotypes, at least one allele was classified as pathogenic or likely pathogenic. In silico variant pathogenicity interpretation tools, combined with structural 3D modeling of variant proteins and applied comparative analysis, have improved the current DDC variant interpretation recommendations, particularly of VUSs.

Clinical and biochemical footprints of inherited metabolic disease. V. Cerebral palsy phenotypes

Cerebral palsy is the most common physical disability of childhood describing a heterogeneous group of neurodevelopmental disorders that cause activity limitation, but often are accompanied by disturbances of sensation, perception, cognition, communication and behavior, or by epilepsy. Inborn errors of metabolism have been reported in the literature as presenting with features of cerebral palsy. We reviewed and updated the list of metabolic disorders known to be associated with symptoms suggestive of cerebral palsy and found more than 150 relevant IEMs. This represents the fifth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnosis according to system involvement.

Clinical and biochemical footprints of inherited metabolic diseases. IX. Metabolic ear disease

Damages to the ear are very diverse and can depend on the type of inherited metabolic diseases (IMD). Indeed, IMDs can affect all parts of the auditory system, from the outer ear to the central auditory process. We have identified 219 IMDs associated with various types of ear involvement which we classified into five groups according to the lesion site of the auditory system: congenital external ear abnormalities, acquired external ear abnormalities, middle ear involvement, inner ear or retrocochlear involvement, and unspecified hearing loss. This represents the ninth issue in a series of educational summaries providing a comprehensive and updated list of metabolic differential diagnoses according to system involvement.

Clinical and biochemical footprints of inherited metabolic disorders: X. Metabolic myopathies

Metabolic myopathies are characterized by the deficiency or dysfunction of essential metabolites or fuels to generate energy for muscle contraction; they most commonly manifest with neuromuscular symptoms due to impaired muscle development or functioning. We have summarized associations of signs and symptoms in 358 inherited metabolic diseases presenting with myopathies. This represents the tenth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Clinical and biochemical footprints of inherited metabolic diseases. VIII. Neoplasias

Cancer, caused by multiple cumulative pathogenic variants in tumor suppressor genes and proto-oncogenes, is a leading cause of mortality worldwide. The uncontrolled and rapid cell growth of the tumors requires a reprogramming of the complex cellular metabolic network to favor anabolism. Adequate management and treatment of certain inherited metabolic diseases might prevent the development of certain neoplasias, such as hepatocellular carcinoma in tyrosinemia type 1 or hepatocellular adenomas in glycogen storage disorder type 1a. We reviewed and updated the list of known metabolic etiologies associated with various types of benign and malignant neoplasias, finding 64 relevant inborn errors of metabolism. This is the eighth article of the series attempting to create a comprehensive list of clinical and metabolic differential diagnosis by system involvement.

Clinical and biochemical footprints of inherited metabolic disorders. VII. Ocular phenotypes

Ocular manifestations are observed in approximately one third of all inherited metabolic disorders (IMDs). Although ocular involvement is not life-threatening, it can result in severe vision loss, thereby leading to an additional burden for the patient. Retinal degeneration with or without optic atrophy is the most frequent phenotype, followed by oculomotor problems, involvement of the cornea and lens, and refractive errors. These phenotypes can provide valuable clues that contribute to its diagnosis. In this issue we found 577 relevant IMDs leading to ophthalmologic manifestations. This article is the seventh of a series attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

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.

Accurate assignment of disease liability to genetic variants using only population data

PURPOSE

The growing size of public variant repositories prompted us to test the accuracy of pathogenicity prediction of DNA variants using population data alone.

METHODS

Under the a priori assumption that the ratio of the prevalence of variants in healthy population vs that in affected populations form 2 distinct distributions (pathogenic and benign), we used a Bayesian method to assign probability to a variant belonging to either distribution.

RESULTS

The approach, termed Bayesian prevalence ratio (BayPR), accurately parsed 300 of 313 expertly curated CFTR variants: 284 of 296 pathogenic/likely pathogenic variants in 1 distribution and 16 of 17 benign/likely benign variants in another. BayPR produced an area under the receiver operating characteristic curve of 0.99 for 103 functionally confirmed missense CFTR variants, which is equal to or exceeds 10 commonly used algorithms (area under the receiver operating characteristic curve range = 0.54-0.99). Application of BayPR to expertly curated variants in 8 genes associated with 7 Mendelian conditions led to the assignment of a disease-causing probability of ≥80% to 1350 of 1374 (98.3%) pathogenic/likely pathogenic variants and of ≤20% to 22 of 23 (95.7%) benign/likely benign variants.

CONCLUSION

Irrespective of the variant type or functional effect, the BayPR approach provides probabilities of pathogenicity for DNA variants responsible for Mendelian disorders using only the variant counts in affected and unaffected population samples.

Clinical and biochemical footprints of inherited metabolic diseases. VI. Metabolic dermatoses

Cutaneous signs and symptoms may facilitate the diagnosis or can help in identifying complications or side effects of overtreatment of inherited metabolic diseases. The principal manifestations can be grouped into vascular lesions, ichthyosis, papular and nodular skin lesions, abnormal pigmentation, photosensitivity, skin laxity, hair shaft involvement, and nail abnormalities. We have summarized associations of these cutaneous signs and symptoms in 252 inherited metabolic diseases. This represents the sixth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

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.

Molecular and metabolic bases of tetrahydrobiopterin (BH4) deficiencies

Tetrahydrobiopterin (BH4) deficiency is caused by genetic variants in the three genes involved in de novo cofactor biosynthesis, GTP cyclohydrolase I (GTPCH/GCH1), 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), sepiapterin reductase (SR/SPR), and the two genes involved in cofactor recycling, carbinolamine-4α-dehydratase (PCD/PCBD1) and dihydropteridine reductase (DHPR/QDPR). Dysfunction in BH4 metabolism leads to reduced cofactor levels and may result in systemic hyperphenylalaninemia and/or neurological sequelae due to secondary deficiency in monoamine neurotransmitters in the central nervous system. More than 1100 patients with BH4 deficiency and 800 different allelic variants distributed throughout the individual genes are tabulated in database of pediatric neurotransmitter disorders PNDdb. Here we provide an update on the molecular-genetic analysis and structural considerations of these variants, including the clinical courses of the genotypes. From a total of 324 alleles, 11 are associated with the autosomal recessive form of GTPCH deficiency presenting with hyperphenylalaninemia (HPA) and neurotransmitter deficiency, 295 GCH1 variant alleles are detected in the dominant form of L-dopa-responsive dystonia (DRD or Segawa disease) while phenotypes of 18 alleles remained undefined. Autosomal recessive variants observed in the PTS (199 variants), PCBD1 (32 variants), and QDPR (141 variants) genes lead to HPA concomitant with central monoamine neurotransmitter deficiency, while SPR deficiency (104 variants) presents without hyperphenylalaninemia. The clinical impact of reported variants is essential for genetic counseling and important for development of precision medicine.

Phenylketonuria

Phenylketonuria (PKU; also known as phenylalanine hydroxylase (PAH) deficiency) is an autosomal recessive disorder of phenylalanine metabolism, in which especially high phenylalanine concentrations cause brain dysfunction. If untreated, this brain dysfunction results in severe intellectual disability, epilepsy and behavioural problems. The prevalence varies worldwide, with an average of about 1:10,000 newborns. Early diagnosis is based on newborn screening, and if treatment is started early and continued, intelligence is within normal limits with, on average, some suboptimal neurocognitive function. Dietary restriction of phenylalanine has been the mainstay of treatment for over 60 years and has been highly successful, although outcomes are still suboptimal and patients can find the treatment difficult to adhere to. Pharmacological treatments are available, such as tetrahydrobiopterin, which is effective in only a minority of patients (usually those with milder PKU), and pegylated phenylalanine ammonia lyase, which requires daily subcutaneous injections and causes adverse immune responses. Given the drawbacks of these approaches, other treatments are in development, such as mRNA and gene therapy. Even though PAH deficiency is the most common defect of amino acid metabolism in humans, brain dysfunction in individuals with PKU is still not well understood and further research is needed to facilitate development of pathophysiology-driven treatments.

Detection of 3-O-methyldopa in dried blood spots for neonatal diagnosis of aromatic L-amino-acid decarboxylase deficiency: The northeastern Italian experience

OBJECTIVE

Aromatic L-amino acid decarboxylase (AADC) deficiency is a rare inherited autosomal recessive disorder of biogenic amine metabolism. Diagnosis requires analysis of neurotransmitter metabolites in cerebrospinal fluid, AADC enzyme activity analysis, or molecular analysis of the DDC gene. 3-O-methyldopa (3-OMD) is a key screening biomarker for AADC deficiency.

METHODS

We describe a rapid method for 3-OMD determination in dried blood spots (DBS) using flow-injection analysis tandem mass spectrometry with NeoBase™ 2 reagents and ¹³C₆-tyrosine as an internal standard, which are routinely used in high-throughput newborn screening. We assessed variability using quality control samples over a range of 3-OMD concentrations.

RESULTS

Within-day and between-day precision determined with quality control samples demonstrated coefficients of variation <15%. 3-OMD concentrations in 1000 healthy newborns revealed a mean of 1.33 μmol/L (SD ± 0.56, range 0.61-3.05 μmol/L), 100 non-AADC control subjects (age 7 days - 1 year) showed a mean of 1.19 μmol/L (SD ± 0.35-2.00 μmol/L), and 81 patients receiving oral L-Dopa had a mean 3-OMD concentration of 14.90 μmol/L (SD ± 14.18, range 0.4-80.3 μmol/L). A patient with confirmed AADC was retrospectively analyzed and correctly identified (3-OMD 10.51 μmol/L). In April 2020, we started a pilot project for identifying AADC deficiency in DBSs routinely submitted to the expanded newborn screening program. 3-OMD concentrations were measured in 21,867 samples; no patients with AADC deficiency were identified. One newborn had a high 3-OMD concentration due to maternal L-Dopa treatment.

DISCUSSION

We demonstrated a rapid new method to identify AADC deficiency using reagents and equipment already widely used in newborn screening programs. Although our study is limited, introduction of our method in expanded neonatal screening is feasible and could facilitate deployment of screening, allowing for early diagnosis that is important for effective treatment.

Clinical and biochemical footprints of inherited metabolic diseases. IV. Metabolic cardiovascular disease

Inherited metabolic diseases account for 15-20% of all cases of pediatric cardiomyopathy, with a high mortality of 15-47%. Metabolic diseases can also commonly be associated with other types of cardiovascular involvement such as arrhythmias, valvulopathy or vasculopathy. We reviewed and updated the list of known metabolic etiologies associated with cardiovascular involvement, and found 246 relevant inborn errors of metabolism. This represents the fourth of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Long-term clinical outcome of 6-pyruvoyl-tetrahydropterin synthase-deficient patients

INTRODUCTION

6-Pyruvoyl-tetrahydropterin synthase deficiency (PTPSd) is a rare autosomal recessive disorder of synthesis of biogenic amines, which is characterized by variable neurological impairment and hyperphenylalaninemia. We aimed to assess the long-term clinical outcome of this disorder and the factors affecting it.

METHODS

At total of 28 PTPSd patients (aged 19.9 ± 10.9 years) underwent clinical (neurological and psychiatric) and neuropsychological assessment (BRIEF, VABS-II, and IQ). Based on CSF homovanillic (HVA) and 5-hydroxyindolacetic acid (5-HIAA) and pterin concentrations at diagnosis, patients were classified as having either a severe [SF; low level of CSF, HVA, and 5-HIAA with altered neopterin/biopterin (Neo/Bio)] or mild form (MF; normal HVA and 5-HIAA with altered Neo/Bio) of PTPSd.

RESULTS

Approximately 36% of patients had MF PTPSd. At the last examination, 43% of patients had movement disorders (2 MF, 10 SF), 43% of patients had variable degrees of intellectual disability (SF only), 39% met the criteria for a psychiatric disorder (3 MF, 9 SF). Applying a linear regression model, we found that HVA and phenylalanine levels at birth had a significant influence on IQ, BRIEF, and VABS-II variability. Lastly, 5-HIAA further contributed to VABS-II variability. The disease showed a self-limiting clinical course and its treatment, although delayed, is effective in improving the neurological status.

CONCLUSIONS

Neurodevelopmental impairment due to PTPSd shows a self-limiting course. A continuous improvement in the neurological condition has been observed in patients receiving treatment, even when delayed. The severity of brain biogenic amine depletion at diagnosis predicts neurological and psychiatric outcomes.

Molecular genetics of phenylketonuria and tetrahydrobiopterin deficiency in Jordan

BACKGROUND

Information regarding the prevalence of PKU in the Middle East in comparison to other world regions is scarce, which might be explained by difficulties in the implementation of national newborn screening programs.

OBJECTIVE

This study seeks for the first time to genotype and biochemically characterize patients diagnosed with hyperphenylalaninemia (HPA) at the Pediatric Metabolic Genetics Clinic at the King Hussein Medical Center, Amman, Jordan.

METHODS

A total of 33 patients with HPA and 55 family members were investigated for pterins (neopterin and biopterin) and dihydropteridine reductase (DHPR) activity in dried blood spots. Patients with HPA were genotyped for phenylketonuria (PKU) and the genes involved in tetrahydrobiopterin (BH4) metabolism.

RESULTS

In total 20 patients were diagnosed with PKU due to phenylalanine hydroxylase (PAH) deficiency, 2 with GTP cyclohydrolase I (GTPCH) deficiency, 6 with DHPR deficiency, and 3 with the 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. Diagnosis was not possible in 2 patients. This study documents a high percentage of BH4 deficiencies within HPA patients. With one exception, all patients were homozygous for particular gene variants.

CONCLUSIONS

This approach enables differentiation between PKU and BH4 deficiencies and, thus, allows for critical selection of a specific treatment strategies.

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.

Targeted cerebrospinal fluid analysis for inborn errors of metabolism on an LC-MS/MS analysis platform

BACKGROUND

Laboratory investigations of cerebrospinal fluid (CSF) are essential when suspecting an inborn error of metabolism (IEM) involving neurological features. Available tests are currently performed on different analytical platforms, requiring a large sample volume and long turnaround time, which often delays timely diagnosis. Therefore, it would be preferable to have an "one-instrument" targeted multi-metabolite approach.

METHOD

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) platform, based on two different methods for analysing 38 metabolites using positive and negative electrospray ionisation modes, was established. To allow for platform extension, both methods were designed to use the same CSF sample preparation procedure and to be run on the same separation column (ACE C18-PFP).

RESULTS

Assessment of the LC-MS/MS platform methods was first made by analytical validation, followed by the establishment of literature-based CSF cut-off values and reference ranges, and by the measurement of available samples obtained from patients with confirmed diagnoses of aromatic l-amino acid decarboxylase deficiency, guanidinoacetate methyltransferase deficiency, ornithine aminotransferase deficiency, cerebral folate deficiency and methylenetetrahydrofolate reductase deficiency.

CONCLUSION

An extendable targeted LC-MS/MS platform was developed for the analysis of multiple metabolites in CSF, thereby distinguishing samples from patients with IEM from non-IEM samples. Reference concentrations for several biomarkers in CSF are provided for the first time. By measurement on a single analytical platform, less sample volume is required (200 μL), diagnostic results are obtained faster, and preanalytical issues are reduced.

SYNOPSIS

LC-MS/MS platform for CSF analysis consisting of two differentially designed methods.

Clinical and biochemical footprints of inherited metabolic diseases. III. Psychiatric presentations

Psychiatric symptoms are common manifestations in many inborn errors of metabolism (IEMs), ranging from attention deficit, anxiety and mood and behavioral disorders to psychosis. Furthermore, IEMs represent a significant percentage of all autism cases. We reviewed and updated the list of metabolic disorders known to be associated with various psychiatric manifestations and found more than 100 relevant IEMs. This represents the third of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to organ system involvement.

The first European guidelines on phenylketonuria: Usefulness and implications for BH4 responsiveness testing

OBJECTIVE

This study aimed to investigate and improve the usefulness of the 48-hour BH4 loading test and to assess genotype for BH4 responsiveness prediction, using the new definition of BH4 responsiveness from the European guidelines, as well as an amended definition.

METHOD

Applying the definition of the European guidelines (≥100% increase in natural protein tolerance) and an amended definition (≥100% increase in natural protein tolerance or tolerating a safe natural protein intake) to a previous dataset, we first assessed the positive predictive value (PPV) of the 48-hour BH4 loading test using a cutoff value of 30%. Then, we tried to improve this PPV by using different cutoff values and separate time points. Last, using the BIOPKU database, we compared predicted BH4 responsiveness (according to genotype) and genotypic phenotype values (GPVs) in BH4 -responsive and BH4 -unresponsive patients.

RESULTS

The PPV of the 48-hour loading test was 50.0% using the definition of the European guidelines, and 69.4% when applying the amended definition of BH4 responsiveness. Higher cutoff values led to a higher PPV, but resulted in an increase in false-negative tests. Parameters for genotype overlapped between BH4 -responsive and BH4 -unresponsive patients, although BH4 responsiveness was not observed in patients with a GPV below 2.4.

CONCLUSION

The 48-hour BH4 loading test is not as useful as previously considered and cannot be improved easily, whereas genotype seems mainly helpful in excluding BH4 responsiveness. Overall, the definition of BH4 responsiveness and BH4 responsiveness testing require further attention.

Genome sequencing identifies a homozygous inversion disrupting QDPR as a cause for dihydropteridine reductase deficiency

Background

Dihydropteridine reductase (DHPR) is one of the key enzymes for maintaining in the organism the supply of tetrahydrobiopterin (BH₄), an essential cofactor for aromatic amino acid hydroxylases. Its dysfunction causes the condition of hyperphenylalaninemia together with the lack of neurotransmitters.

Methods

We report a patient with biochemically diagnosed DHPR deficiency, with extensive molecular investigations undertaken to detect variations in quinoid dihydropteridine reductase (QDPR) gene. Sanger sequencing of QDPR coding regions, exome sequencing, QDPR mRNA PCR, and karyotyping were followed by trio genome sequencing.

Results

Short‐read genome sequencing revealed a homozygous 9‐Mb inversion disrupting QDPR. Structural variant breakpoints in chromosome 4 were located to intron 2 of QDPR at Chr4(GRCh38):g.17505522 and in intron 8 of the ACOX3 gene, Chr4(GRCh38):g.8398067). Both nonrelated parents carried the variant in heterozygous state. The inversion was not present in gnomAD structural variant database.

Conclusion

Identification of the exact breakpoints now allows further straightforward molecular genetic testing of potential carriers of the inversion. This study extends the pathogenic variant spectrum of DHPR deficiency and highlights the role of structural variants in recessive metabolic disorders. To our knowledge, this is the first report on a large, canonical (rather than complex) homozygous pathogenic inversion detected by genome sequencing.

Use of a Ruthenium(III), Iron(II), and Nickel(II) Hexacyanometallate-Modified Graphite Electrode with Immobilized Oxalate Oxidase for the Determination of Urinary Oxalate

This paper describes the performance of a biosensor with an Ru(III), Ni(II), and Fe(II) hexacyanometallate-modified graphite electrode and immobilized oxalate oxidase for the determination of urinary oxalate. The addition of ruthenium enhances the electrochemical reversibility and chemical stability of the electrocrystallized layer and improves the sensitivity of the biosensor. Hydrogen peroxide, produced by the enzyme-catalyzed oxidation of oxalate, was measured at −50 mV vs an Hg|Hg2Cl2|3M KCl electrode in a solution of pH 3.6 succinic buffer, 0.1M KCl, and 5.4mM ethylenediaminetetraacetic acid. The linear concentration range for the determination of oxalate was 0.18–280 μM. The recoveries of added oxalate (10–35 μM) from aqueous solution ranged from 99.5 to 101.7%, whereas from urine samples without oxalate (or with a concentration of oxalate below the detection limit) the recoveries of added oxalate ranged from 91.4 to 106.6%. The oxalate in 24 h urine samples, taken during their daily routine from 35 infants and children, was measured and found to range from 0.6 to 121.7 mg/L. There were no interferences from uric acid, acetylsalicylic acid, and urea in the concentration range investigated, but paracetamol and ascorbic acid did interfere. A good correlation (R2 = 0.9242) was found between values obtained for oxalate in real urine samples by 2 laboratories, with the proposed biosensor and ion chromatography, respectively.

Unique aspects of sequence variant interpretation for inborn errors of metabolism (IEM): The ClinGen IEM Working Group and the Phenylalanine Hydroxylase Gene

The ClinGen Inborn Errors of Metabolism Working Group was tasked with creating a comprehensive, standardized knowledge base of genes and variants for metabolic diseases. Phenylalanine hydroxylase (PAH) deficiency was chosen to pilot development of the Working Group's standards and guidelines. A PAH variant curation expert panel (VCEP) was created to facilitate this process. Following ACMG-AMP variant interpretation guidelines, we present the development of these standards in the context of PAH variant curation and interpretation. Existing ACMG-AMP rules were adjusted based on disease (6) or strength (5) or both (2). Disease adjustments include allele frequency thresholds, functional assay thresholds, and phenotype-specific guidelines. Our validation of PAH-specific variant interpretation guidelines is presented using 85 variants. The PAH VCEP interpretations were concordant with existing interpretations in ClinVar for 69 variants (81%). Development of biocurator tools and standards are also described. Using the PAH-specific ACMG-AMP guidelines, 714 PAH variants have been curated and will be submitted to ClinVar. We also discuss strategies and challenges in applying ACMG-AMP guidelines to autosomal recessive metabolic disease, and the curation of variants in these genes.

Exploratory study of the effect of one week of orally administered CNSA-001 (sepiapterin) on CNS levels of tetrahydrobiopterin, dihydrobiopterin and monoamine neurotransmitter metabolites in healthy volunteers

Tetrahydrobiopterin (BH₄) is a cofactor for the enzymes tyrosine hydroxylase and tryptophan hydroxylase, the rate-limiting enzymes in the production of the neurotransmitters, dopamine and serotonin, respectively, in the central nervous system (CNS). Administration of BH₄ is used clinically within the management of persons with genetic BH₄ deficiencies, but the BH₄ molecule does not cross the blood-brain barrier sufficiently. CNSA-001 is a pharmaceutical preparation of sepiapterin, a natural precursor of BH₄ that induced larger increases in plasma BH₄ compared with administration of the same doses of BH₄ itself in healthy volunteers in a randomized trial. Here, we report the effects of 7 days of once-daily treatment with CNSA-001 60 mg/kg (n = 6) or placebo (n = 2) on metabolites of the BH₄ synthetic pathway and on biomarkers of the serotonin (5-hydroxyindoleacetic acid [5-HIAA]) and dopamine (homovanillic acid [HVA]) pathways in cerebrospinal fluid (CSF) in subjects from this trial. There were no notable changes in any metabolite in placebo-treated subjects. Administration of CNSA-001 increased mean BH₄ from 18.1 (SD 3.0) to 35.1 (10.0) nmol/L, and of dihydrobiopterin (BH₂) from 2.1 (0.3) to 7.9 (1.5) nmol/L. Overall, administration of CNSA-001 had little effect on mean levels (pre- vs. post-treatment) of 5-HIAA (76.1 [SD 29.8] vs. 70.1 [23.1] nmol/L) or HVA (177.2 [66.5] vs. 184.8 [35.3]) nmol/L. One subject with low 5-HIAA and HVA at baseline responded with approximately three-fold increases in CNS levels of these metabolites after CNSA-001 treatment, with post-treatment levels within the range of those seen in other subjects. Administration of CNSA-001 60 mg/kg markedly increased levels of BH₄ in the CNS of healthy volunteers, with apparently little overall effect in CNS levels of already normal key neurotransmitter metabolites.

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Tetrahydrobiopterin (BH₄) is a cofactor of enzymes involved in production of central neurotransmitters dopamine and serotonin

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Healthy volunteers were randomized to receive a once daily doses of CNSA-001 (sepiapterin) or placebo for 7 days

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Oral CNSA-001 administration increased levels of BH₄ and 7,8-dihydrobiopterin (BH₂) in cerebrospinal fluid

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Normal base levels of metabolites of serotonin (5-HIAA) or dopamine (HVA) were unaffected

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Abnormally low baseline levels of 5-HIAA and HVA in one patient increased to normal ranges following CNSA-001 administration

6-Pyruvoyltetrahydropterin Synthase Deficiency: Review and Report of 28 Arab Subjects

BACKGROUND

Tetrahydrobiopterin is an essential cofactor for the hydroxylation of aromatic amino acids phenylalanine, tyrosine, and tryptophan. Therefore, tetrahydrobiopterin deficiency results in hyperphenylalaninemia as well as dopamine and serotonin depletion in the central nervous system. The enzyme 6-pyruvoyltetrahydropterin synthase catalyzes the second step of de novo synthesis of tetrahydrobiopterin, and its deficiency is the most frequent cause of tetrahydrobiopterin metabolism disorders.

METHOD

We conducted a retrospective chart review of 28 subjects from 24 families with molecularly confirmed 6-pyruvoyltetrahydropterin synthase deficiency from six centers in three Arab countries. We reviewed clinical, biochemical, and molecular data. We also reviewed previously published cohorts of subjects with 6-pyruvoyltetrahydropterin synthase deficiency.

RESULTS

Similar to previous observations, we show that early treatment (less than two months) is associated with better outcome. We identify eight PTS variants in 24 independent families. The most common variant is (c.238A>G; p.M80V) with an allele count of 33%. We also identify one novel variant (c.2T>G; p.?).

CONCLUSION

The deficiency of 6-pyruvoyltetrahydropterin synthase is relatively common in the Arab population and should be considered in individuals with hyperphenylalaninemia. More natural history studies with comprehensive biochemical and molecular genetics data are needed for a robust base for the development of future therapy.

Clinical and biochemical footprints of inherited metabolic diseases. II. Metabolic liver diseases

Inherited metabolic diseases account for about one third of pediatric patients with hepatomegaly, acute liver failure, cirrhosis or cholestasis. Specifically for pediatric acute liver failure, they account for 10-15% of cases, with a mortality of 22-65%. The percentage of acute liver failure caused by an inherited metabolic disease in children <2-3 years of age is even higher, ranging from a third to half of all cases. Metabolic liver disease accounts for 8-13% of all pediatric liver transplantations. Despite this high burden of disease, underdiagnosis remains common. We reviewed and updated the list of known metabolic etiologies associated with various types of metabolic liver involvement, and found 142 relevant inborn errors of metabolism. This represents the second of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Aromatic amino acid decarboxylase deficiency: Molecular and metabolic basis and therapeutic outlook

Aromatic-l-amino acid decarboxylase (AADC) deficiency is an ultra-rare inherited autosomal recessive disorder characterized by sharply reduced synthesis of dopamine as well as other neurotransmitters. Symptoms, including hypotonia and movement disorders (especially oculogyric crisis and dystonia) as well as autonomic dysfunction and behavioral disorders, vary extensively and typically emerge in the first months of life. However, diagnosis is difficult, requiring analysis of metabolites in cerebrospinal fluid, assessment of plasma AADC activity, and/or DNA sequence analysis, and is frequently delayed for years. New metabolomics techniques promise early diagnosis of AADC deficiency by detection of 3-O-methyl-dopa in serum or dried blood spots. A total of 82 dopa decarboxylase (DDC) variants in the DDC gene leading to AADC deficiency have been identified and catalogued for all known patients (n = 123). Biochemical and bioinformatics studies provided insight into the impact of many variants. c.714+4A>T, p.S250F, p.R347Q, and p.G102S are the most frequent variants (cumulative allele frequency = 57%), and c.[714+4A>T];[714+4A>T], p.[S250F];[S250F], and p.[G102S];[G102S] are the most frequent genotypes (cumulative genotype frequency = 40%). Known or predicted molecular effect was defined for 79 variants. Most patients experience an unrelenting disease course with poor or no response to conventional medical treatments, including dopamine agonists, monoamine oxidase inhibitors, and pyridoxine derivatives. The advent of gene therapy represents a potentially promising new avenue for treatment of patients with AADC deficiency. Clinical studies based on the direct infusion of engineered adeno-associated virus type 2 vectors into the putamen have demonstrated acceptable safety and tolerability and encouraging improvement in motor milestones and cognitive symptoms. The success of gene therapy in AADC deficiency treatment will depend on timely diagnosis to facilitate treatment administration before the onset of neurologic damage.

Cerebrospinal fluid biogenic amines depletion and brain atrophy in adult patients with phenylketonuria

Biogenic amines synthesis in phenylketonuria (PKU) patients with high phenylalanine (Phe) concentration is thought to be impaired due to inhibition of tyrosine and tryptophan hydroxylases and competition with amino acids at the blood-brain barrier. Dopamine and serotonin deficits might explain brain damage and progressive neuropsychiatric impairment in adult PKU patients. Ten early treated adult PKU patients (mean age 38.2 years) and 15 age-matched controls entered the study. Plasma and cerebrospinal fluid (CSF) Phe, 5-hydroxyindoleacetic acid (5-HIAA), 5-hydroxytryptophan (5-HTP), 3,4-dihydroxy-l-phenylalanine (l-DOPA) and homovanillic acid (HVA) were analyzed. Voxel-based morphometry statistical nonparametric mapping was used to test the age-corrected correlation between gray matter atrophy and CSF biogenic amines levels. 5-HIAA and 5-HTP were significantly reduced in PKU patients compared to controls. Significant negative correlations were found between CSF 5-HIAA, HVA, and 5-HTP and Phe levels. A decrease in 5-HIAA and 5-HTP concentrations correlated with precuneus and frontal atrophy, respectively. Lower HVA levels correlated with occipital atrophy. Biogenic amines deficits correlate with specific brain atrophy patterns in adult PKU patients, in line with serotonin and dopamine projections. These findings may support a more rigorous Phe control in adult PKU to prevent neurotransmitter depletion and accelerated brain damage due to aging.

Clinical and biochemical footprints of inherited metabolic diseases. I. Movement disorders

About a third of patients with inherited metabolic diseases with neurologic involvement suffer from a movement disorder, in the form of ataxia, hyperkinetic movements, or hypokinetic-rigid syndrome. We reviewed and updated the list of known metabolic etiologies associated with various types of movement disorders, and found approximately 200 relevant inborn errors of metabolism. This represents the first of a series of articles attempting to create and maintain a comprehensive list of clinical and metabolic differential diagnoses according to system involvement.

Phase I clinical evaluation of CNSA-001 (sepiapterin), a novel pharmacological treatment for phenylketonuria and tetrahydrobiopterin deficiencies, in healthy volunteers

Tetrahydrobiopterin (BH4) is the natural cofactor of aromatic amino acid hydroxylases and essential for degradation of phenylalanine and synthesis of catecholamines and serotonin. It can be synthesized either de novo from GTP or through the salvage pathway from sepiapterin. Sepiapterin, a natural precursor of BH4, is a more stable molecule and is transported more efficiently across cellular membranes, thus having potentially significant advantage over BH4 as a pharmacological agent for diseases associated with BH4-deficient conditions. We report the results of a first-in-humans, randomized, double-blind, placebo-controlled, dose-ranging, Phase I clinical trial in 83 healthy volunteers of CNSA-001, a novel formulation of sepiapterin. Single oral doses of 2.5-80 mg/kg CNSA-001 caused dose-related increases in plasma sepiapterin (mean Cmax 0.58-2.92 ng/mL) and BH4 (mean Cmax 57-312 ng/mL). Maximum plasma concentrations were achieved in about 1-2 h (sepiapterin) or about 4 h (BH4) after CNSA-001 oral intake. Increases in plasma BH4 were substantially larger in absolute terms and on a dose-for-dose basis following treatment with CNSA-001 vs. sapropterin dihydrochloride, a synthetic form of BH4. The pharmacokinetics of plasma sepiapterin and BH4 were similar before and after seven days of repeat daily dosing with CNSA-001 at 5, 20 or 60 mg/kg indicating little or no drug accumulation. Oral administration of CNSA-001 resulted in higher concentrations of sepiapterin in fasted vs. fed subjects, but overall BH4 plasma exposure following CNSA-001 intake increased by 1.7-1.8-fold in fed subjects. CNSA-001 was well tolerated, with no clear dose-relationship for adverse events (AE), no serious AE and no study discontinuations for AE. These data indicate that CNSA-001 is rapidly and efficiently converted to BH4 in humans supporting further clinical evaluation of CNSA-001 for the management of PKU, primary BH4 deficiencies and other diseases associated with deficient BH4 metabolism.

Phenylalanine hydroxylase variants interact with the co-chaperone DNAJC12

DNAJC12, a type III member of the HSP40/DNAJ family, has been identified as the specific co-chaperone of phenylalanine hydroxylase (PAH) and the other aromatic amino acid hydroxylases. DNAJ proteins work together with molecular chaperones of the HSP70 family to assist in proper folding and maintenance of intracellular stability of their clients. Autosomal recessive mutations in DNAJC12 were found to reduce PAH levels, leading to hyperphenylalaninemia (HPA) in patients without mutations in PAH. In this work, we investigated the interaction of normal wild-type DNAJC12 with mutant PAH in cells expressing several PAH variants associated with HPA in humans, as well as in the Enu^1/1 mouse model, homozygous for the V106A-Pah variant, which leads to severe protein instability, accelerated PAH degradation and mild HPA. We found that mutant PAH exhibits increased ubiquitination, instability, and aggregation compared with normal PAH. In mouse liver lysates, we showed that DNAJC12 interacts with monoubiquitin-tagged PAH. This form represented a major fraction of PAH in the Enu^1/1 but was also present in liver of wild-type PAH mice. Our results support a role of DNAJC12 in the processing of misfolded ubiquitinated PAH by the ubiquitin-dependent proteasome/autophagy systems and add to the evidence that the DNAJ proteins are important players both for proper folding and degradation of their clients.

Metabolic Evaluation of Epilepsy: A Diagnostic Algorithm With Focus on Treatable Conditions

Although inborn errors of metabolism do not represent the most common cause of seizures, their early identification is of utmost importance, since many will require therapeutic measures beyond that of common anti-epileptic drugs, either in order to control seizures, or to decrease the risk of neurodegeneration. We translate the currently-known literature on metabolic etiologies of epilepsy (268 inborn errors of metabolism belonging to 21 categories, with 74 treatable errors), into a 2-tiered diagnostic algorithm, with the first-tier comprising accessible, affordable, and less invasive screening tests in urine and blood, with the potential to identify the majority of treatable conditions, while the second-tier tests are ordered based on individual clinical signs and symptoms. This resource aims to support the pediatrician, neurologist, biochemical, and clinical geneticists in early identification of treatable inborn errors of metabolism in a child with seizures, allowing for timely initiation of targeted therapy with the potential to improve outcomes.