Long-term follow-up of tetrahydrobiopterin therapy in patients with tetrahydrobiopterin deficiency in Japan

Biochemical and molecular features of tetrahydrobiopterin deficiency in Fujian Province, southeastern China

The estimated prevalence of tetrahydrobiopterin deficiency (BH4D) and the mutational spectrum of the causal 6-pyruvoyl-tetrahydropterin synthase (PTS) gene vary widely according to race and region. This study assessed the prevalence and genetic characteristics of BH4D in Fujian Province, southeastern China. A total of 3,204,067 newborns were screened between 2012 and 2022 based on the phenylalanine level and the phenylalanine/tyrosine ratio in dried blood spots. Differential diagnosis was determined by the urine purine spectrum, dihydropteridine reductase activity in red blood cells, and genetic testing. The PTS mutation spectrum and genotypes were determined by next-generation sequencing. A total of 189 newborns were diagnosed with hyperphenylalaninemia (HPA) over the study period, including 159 with phenylalanine hydroxylase deficiency and 30 with BH4D. Therefore, the prevalence of BH4D in Fujian was 9.36 per 1,000,000 live births (30/3,204,067) and the proportion of BH4D among patients with HPA was 15.87% (30/189). A total of 58 PTS alleles were identified in the 29 patients with PTS deficiency (PTPSD), and those alleles were composed of 10 different variants, including eight missense variants and two splice-site variants. The most prevalent variants were c.155A>G, p.Asn52Ser (44.83%); c.259C>T, p.Pro87Ser (39.66%); and c.84-291A>G, p.Tyr27Argfs*8 (3.45%). The predominant genotype was c [155A>G]; [259C>T] (11/29, 37.93%). The prevalence of BH4D and the spectrum of associated PTS mutations were successfully determined for the first time in Fujian Province, southeastern China. Since the mutation spectrum of PTS is region-specific, such data will facilitate molecular diagnosis and genetic counseling in PTPSD cases.

Two Cases of 6-Pyruvoyl Tetrahydropterin Synthase Deficiency: Case Report and Literature Review

6-pyruvoyl tetrahydropterin synthase deficiency (PTPSD) is a rare neurometabolic disease that can be diagnosed in newborn screening (NBS) and is part of the family of tetrahydrobiopterin deficiency disorders (BH4Ds). It is essential to diagnose and treat this disease early to prevent permanent neurological damage secondary to this neurotransmitter disorder. We present the first two cases of PTPSD in Romania that were genetically confirmed and treated late. Improving the diagnosis and monitoring procedures in Romania with correct metabolic management will prevent severe neurological impairment from PTPSD or other BH4Ds.

Mutation spectrum of PTS gene in patients with tetrahydrobiopterin deficiency from jiangxi province

Background: Hyperphenylalaninemia (HPA) is the most common inborn error in amino acid metabolism. It can be primarily classified into phenylalanine hydroxylase (PAH) deficiency and tetrahydrobiopterin (BH4) deficiency. BH4 deficiency (BH4D) is caused by genetic defects in enzymes involved in the biosynthesis and regeneration of BH4. 6-pyruvoyl-tetrahydropterin synthase (PTPS/PTS), which is encoded by the PTS gene, participates in the biosynthesis of BH4. PTPS deficiency (PTPSD) is the major cause of BH4D. In this study, we investigated that the prevalence of BH4D in Jiangxi province was approximately 12.5 per 1,000,000 live births (69/5,541,627). Furthermore, the frequency of BH4D was estimated to be 28.8% (69/240) in the HPA population of Jiangxi. In this study, we aimed to characterize the mutational spectrum of the PTS gene in patients with PTPSD from Jiangxi province. Method: Newborn screening data of Jiangxi province from 1997 to 2021 were analyzed and 53 families with PTPSD were enrolled for the analysis of the PTS gene variants by Sanger sequencing. Results: 106 variants were identified in 106 alleles of 53 patients with PTPSD, including 13 types of variants reported previously, and two novel variants (c.164-36A>G and c.146_147insTG). The predominant variant was c.259C>T (47.2%), followed by c.84-291A>G (19.8%), c.155A>G (8.5%), c.286G>A (6.6%) and c.379C>T (4.7%). Conclusion: The results of this study can not only provide guidance for the molecular diagnosis and genetic counseling in cases of PTPS deficiency but also enrich the PTS mutation database.

Disorders of Tetrahydrobiopterin Metabolism: Experience from South India

BACKGROUND

Disorders of tetrahydrobiopterin metabolism represent a rare group of inherited neurotransmitter disorders that manifests mainly in infancy or childhood with developmental delay, neuroregression, epilepsy, movement disorders, and autonomic symptoms.

METHODOLOGY

A retrospective review of genetically confirmed cases of disorders of tetrahydrobiopterin metabolism over a period of three years (Jan 2018 to Jan 2021) was performed across two paediatric neurology centres from South India.

RESULTS

A total of nine patients(M:F=4:5) fulfilled the eligibility criteria. The genetic variants detected include homozygous mutations in the QDPR(n=6), GCH1(n=2), and PTS(n=1) genes. The median age at onset of symptoms was 6-months(range 3-78 months), while that at diagnosis was 15-months (8-120 months), resulting in a median delay in diagnosis of 9-months. The main clinical manifestations included neuroregression (89%), developmental delay(78%), dystonia(78%) and seizures(55%). Management strategies included a phenylalanine restricted diet, levodopa/carbidopa, 5-Hydroxytryphtophan, and folinic acid. Only, Patient-2 afforded and received BH4 supplementation at a sub-optimal dose later in the disease course. We had a median duration of follow up of 15 months (range 2-48 months). Though the biochemical response has been marked; except for patients with GTPCH deficiency, only mild clinical improvement was noted with regards to developmental milestones, seizures, or dystonia in others.

CONCLUSION

Tetrahydrobiopterin deficiencies represent a rare yet potentially treatable cause for non-phenylketonuria hyperphenylalaninemia with better outcomes when treated early in life. Screening for disorders of biopterin metabolism in patients with hyperphenylalaninemia prevents delayed diagnosis. This study expands the genotype-phenotype spectrum of patients with disorders of tetrahydrobiopterin metabolism from South India.

Retrospective analysis of 19 patients with 6-Pyruvoyl Tetrahydropterin Synthase Deficiency: Prolactin levels inversely correlate with growth

BACKGROUND

Pyruvoyl Tetrahydropterin Synthase (PTPS) Deficiency is the most common form of BH4 deficiency resulting in hyperphenylalaninemia. It can have variable clinical severity and there is limited information on the clinical presentation, natural history and effectiveness of newborn screening for this condition.

METHODS

Retrospective data (growth and clinical parameters, biochemical and genetic testing results, treatment) were collected from 19 patients with PTPS deficiency in different centers, to evaluate biochemical and clinical outcomes. Descriptive statistics was used for qualitative variables, while linear regression analysis was used to correlate quantitative variables.

RESULTS

Patients with PTPS deficiency had an increased incidence of prematurity (4/18) with an average gestational age only mildly reduced (37.8 ± 2.4 weeks) and low birth weight (-1.14 ± 0.97 SD below that predicted for gestational age). With time, weight and height approached normal.

VALUES

All patients were identified by newborn screening for an elevated phenylalanine level. However, phenylalanine levels were normal in two whose testing was performed at or before 24 h of age. Sapropterin dihydrochloride treatment normalized phenylalanine levels. Molecular testing identified novel variants in the PTS gene, some of which present in more than one affected family. The neurotransmitter derivatives 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) in the CSF were decreased in most cases except in 2 families with the peripheral form of PTPS deficiency. With time, HVA and 5HIAA became abnormally low in two of these patients requiring therapy. Prolactin (whose secretion is inhibited by dopamine) levels were elevated in several patients with PTPS deficiency and inversely correlated with the z-scores for height (p < 0.01) and weight (p < 0.05). Most patients with PTPS deficiency had delayed development early in life, improving around school age with IQs mostly in the normal range, with a small decline in older individuals. From a neurological standpoint, most patients had normal brain MRI and minor EEG anomalies, although some had persistent neurological symptoms.

DISCUSSION

Patients with PTPS deficiency have not only an increased incidence of prematurity, but also decreased birth weight when corrected for gestational age. Hyperphenylalaninemia can be absent in the first day of life. Therapy with sapropterin dihydrochloride normalizes phenylalanine levels and neurotransmitter precursors can improve CSF neurotransmitter metabolites levels. Insufficient dopaminergic stimulation (as seen from elevated prolactin) might result in decreased height in patients with PTPS deficiency. Despite early delays in development, many patients can achieve independence in adult life, with usually normal neuroimaging and EEG.

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.

Pregnancy management and outcome in patients with four different tetrahydrobiopterin disorders

INTRODUCTION

Inborn errors of tetrahydrobiopterin (BH4) biosynthesis or recycling are a group of very rare neurometabolic diseases. Following growing awareness and improved availability of drug treatment the number of patients with BH4 disorders reaching adulthood is constantly increasing. Pregnancy care of patients with these disorders is therefore a new challenge for clinicians.

METHODS

This retrospective study summarises for the first time clinical and biochemical monitoring data of 16 pregnancies in seven women with different disorders of BH4 metabolism and evaluates treatment regimens before and during pregnancy in relation to the obstetrical outcome and paediatric follow-up.

RESULTS

Worsening of pre-existing neurological symptoms or occurrence of new symptoms during pregnancy was not observed in most of the cases. Treatment regimens remained mostly unchanged. Pregnancies were not complicated by disease-specific features. Organ abnormalities, miscarriage, prematurity, IUGR and chromosomal changes were occasionally reported, without showing any association with the standard drug treatment for BH4 deficiencies.

CONCLUSION

Although our data on 16 pregnancies in seven patients did not present any association of standard drug treatment with an increased rate of pregnancy complications, abnormal obstetrical or paediatric outcome, an intensive clinical and biochemical supervision by a multidisciplinary team before, during and after the pregnancy in any BH4 deficiency is essential since available data on pregnancies in patients with BH4 deficiencies is limited.

Mutational spectrum of PTS gene and in silico pathological assessment of a novel variant in Mexico

BACKGROUND

Tetrahydrobiopterin (BH4) is the cofactor for 6-pyruvoyl-tetrahydropterin synthase (PTPS); it is involved in BH4 biosynthesis and is encoded by PTS gene. Its deficiency (PTPSD) is characterized by hyperphenylalaninemia (HPA) and deficit in central monoamine neurotransmitters. We describe the clinical and mutational spectrum of five patients with PTPSD, from four unrelated Mexican families. All patients had symptomatic diagnosis and presented severe early neurological manifestations and HPA.

METHODS

Clinical and biochemical data from studied patients were recorded. Responsible PTPSD genotypes was determined by direct and bidirectional Sanger DNA sequencing of the six PTS coding exons and their exon-intron borders, and these were directly searched in the available relatives. The novel PTS missense variant [NM_3000317.2:331G > T, p.(Ala111Ser)] was subjected to in silico, to predict a possible deleterious effect.

RESULTS

Diminished fetal movements were perceived as a uniform characteristic in the studied group. DNA sequencing showed two known p.(Arg25∗) and p.(Val132TyrFs∗19) and the novel missense p.(Ala111Ser) PTS variants, the latter representing potentially a frequent PTPSD-responsible allele (50%, 4/8) in Mexican patients. In silico protein modeling analysis of the p.(Ala111Ser) variant revealed loss of hydrophobic interactions between the alanine and neighboring valines, suggesting that these changes in polarity may be detrimental for enzyme function, structure and/or stability.

CONCLUSIONS

This work contributes to the knowledge of PTPS molecular spectrum. The delayed diagnosis of these patients emphasizes the importance of considering BH4 metabolism defects in the differential diagnosis of HPA, especially for countries that are beginning their HPA newborn screening programs.

Sapropterin is safe and effective in patients less than 4-years-old with BH4-responsive phenylalanine hydrolase deficiency

OBJECTIVE

To assess the safety and efficacy of tetrahydrobiopterin therapy with sapropterin to treat tetrahydrobiopterin (BH4)-responsive phenylalanine hydroxylase (PAH) deficiency in children aged <4 years compared with those aged ≥4 years.

STUDY DESIGN

We analyzed a longitudinal follow-up study conducted in all patients with BH4-responsive PAH deficiency throughout Japan. At the end of 2011, 43 patients were receiving sapropterin, of whom 21 were aged <4 years at the initiation of treatment. The starting dose of sapropterin was ≥10 mg/kg/day in 11 of these 21 patients. The duration of follow-up was ≥4 years in 6 of those 11 patients; 3 of these 6 were followed for ≥10 years. Nine patients were receiving sapropterin monotherapy at the end of 2011.

RESULTS

Serum phenylalanine level was maintained within the recommended optimal control range in all 21 patients who started sapropterin treatment before age 4 years. Only 1 nonserious adverse drug reaction occurred, an elevated alanine aminotransferase level in 1 patient. No significant abnormal behavior related to nerve disorders was reported.

CONCLUSION

Sapropterin therapy initiated before age 4 years was effective in maintaining serum phenylalanine level within the favorable range and was safe in Japanese patients with BH4-responsive PAH deficiency.

Clinical characteristics of epileptic seizures in a case of dihydropteridine reductase deficiency

We assessed the clinical characteristics and efficacy of neurotransmitters and levetiracetam in a patient with hyperphenylalaninemia due to dihydropteridine reductase (DHPR) deficiency who developed epileptic seizures. A boy with DHPR deficiency, who had been successfully treated with tetrahydrobiopterin (BH4), levodopa, and 5-hydroxytryptophan (5-HTP) since he was 2 months old, started having monthly episodes of blurred vision, loss of consciousness, and falls at the age of 12 years. He was taking BH4 510 mg/day, levodopa 670 mg/day, 5-HTP 670 mg/day, and entacapone 300 mg/day. We evaluated the seizure semiology, EEG findings, and efficacy of levodopa, 5-HTP, and levetiracetam (LEV). His seizures were comprised of an abrupt loss of awareness and eye deviation to the right. Interictal EEG showed slightly slow posterior-dominant rhythm in 7-8 Hz; intermittent, irregular slowing in the bilateral parieto-occipital region; and multiregional independent spikes in bilateral hemispheres. Ictal EEG showed a seizure pattern starting at the left temporal region. Brain MRI showed diffuse signal increase of deep white matter on T2-weighted and FLAIR images. Dosage increase of levodopa to 1340 mg/day, of 5-HTP to 1500 mg/day, or of both did not suppress seizures. Levetiracetam 2000 mg/day markedly reduced seizures without any adverse events. Patients with DHPR deficiency can develop epileptic seizures of partial onset which can be successfully and safely treated with LEV.

Phenylalanine hydroxylase deficiency: diagnosis and management guideline

Phenylalanine hydroxylase deficiency, traditionally known as phenylketonuria, results in the accumulation of phenylalanine in the blood of affected individuals and was the first inborn error of metabolism to be identified through population screening. Early identification and treatment prevent the most dramatic clinical sequelae of the disorder, but new neurodevelopmental and psychological problems have emerged in individuals treated from birth. The additional unanticipated recognition of a toxic effect of elevated maternal phenylalanine on fetal development has added to a general call in the field for treatment for life. Two major conferences sponsored by the National Institutes of Health held >10 years apart reviewed the state of knowledge in the field of phenylalanine hydroxylase deficiency, but there are no generally accepted recommendations for therapy. The purpose of this guideline is to review the strength of the medical literature relative to the treatment of phenylalanine hydroxylase deficiency and to develop recommendations for diagnosis and therapy of this disorder. Evidence review from the original National Institutes of Health consensus conference and a recent update by the Agency for Healthcare Research and Quality was used to address key questions in the diagnosis and treatment of phenylalanine hydroxylase deficiency by a working group established by the American College of Medical Genetics and Genomics. The group met by phone and in person over the course of a year to review these reports, develop recommendations, and identify key gaps in our knowledge of this disorder. Above all, treatment of phenylalanine hydroxylase deficiency must be life long, with a goal of maintaining blood phenylalanine in the range of 120-360 µmol/l. Treatment has predominantly been dietary manipulation, and use of low protein and phenylalanine medical foods is likely to remain a major component of therapy for the immediate future. Pharmacotherapy for phenylalanine hydroxylase deficiency is in early stages with one approved medication (sapropterin, a derivative of the natural cofactor of phenylalanine hydroxylase) and others under development. Eventually, treatment of phenylalanine hydroxylase deficiency will be individualized with multiple medications and alternative medical foods available to tailor therapy. The primary goal of therapy should be to lower blood phenylalanine, and any interventions, including medications, or combination of therapies that help to achieve that goal in an individual, without other negative consequences, should be considered appropriate therapy. Significant evidence gaps remain in our understanding of the optimum therapies for phenylalanine hydroxylase deficiency, nonphenylalanine effects of these therapies, and long-term sequelae of even well-treated disease in children and adults.