Molecular analysis and long-term follow-up of patients with different forms of 6-pyruvoyl-tetrahydropterin synthase deficiency

Genetic Landscape and Clinical Features of Hyperphenylalaninemia in North Ossetia-Alania: High Frequency of P281L and P211T Genetic Variants in the PAH Gene

This study, conducted in the Republic of North Ossetia-Alania (RNOA), aimed to explore the genetic landscape of hyperphenylalaninemia (HPA) and phenylketonuria (PKU) in the Ossetian population using data from newborn screening (NBS). Through comprehensive molecular genetic analysis of 29 patients with HPA from diverse ethnic backgrounds, two major genetic variants in the PAH gene, P281L and P211T, were identified, constituting 50% of all detected pathogenic alleles in Ossetian patients. Remarkably, these variants exhibited an exceptionally high frequency in the Ossetian population, surpassing global prevalence rates. This study unveiled a notable prevalence of mild forms of HPA (78%), underscoring the importance of genetic counseling for carriers of pathogenic variants in the PAH gene. Moreover, the findings emphasized the necessity for ongoing monitoring of patients with mild forms, as they may lack significant symptoms for diagnosis, potentially impacting offspring. Overall, this research offers valuable insights into the genetic landscape of HPA and PKU in the Ossetian population.

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.

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.

Phenotypes and Genotypes of Inherited Disorders of Biogenic Amine Neurotransmitter Metabolism

Inherited disorders of biogenic amine metabolism are genetically determined conditions resulting in dysfunctions or lack of enzymes involved in the synthesis, degradation, or transport of dopamine, serotonin, adrenaline/noradrenaline, and their metabolites or defects of their cofactor or chaperone biosynthesis. They represent a group of treatable diseases presenting with complex patterns of movement disorders (dystonia, oculogyric crises, severe/hypokinetic syndrome, myoclonic jerks, and tremors) associated with a delay in the emergence of postural reactions, global development delay, and autonomic dysregulation. The earlier the disease manifests, the more severe and widespread the impaired motor functions. Diagnosis mainly depends on measuring neurotransmitter metabolites in cerebrospinal fluid that may address the genetic confirmation. Correlations between the severity of phenotypes and genotypes may vary remarkably among the different diseases. Traditional pharmacological strategies are not disease-modifying in most cases. Gene therapy has provided promising results in patients with DYT-DDC and in vitro models of DYT/PARK-SLC6A3. The rarity of these diseases, combined with limited knowledge of their clinical, biochemical, and molecular genetic features, frequently leads to misdiagnosis or significant diagnostic delays. This review provides updates on these aspects with a final outlook on future perspectives.

Genetic evaluation of hyperphenylalaninemia patients with tetrahydrobiopterin deficiency in Iranian population: Identification of four novel disease-causing variants

BACKGROUND

Hyperphenylalaninemia (HPA) is the most common inborn error of amino acid metabolism worldwide. At least 2% of HPA cases are caused by a deficiency in tetrahydrobiopterin (BH4) metabolism. Genes such as QDPR and PTS are essential in the BH4 metabolism. This study aims to identify disease-causing variants in HPA patients, which may be helpful in genetic counseling and prenatal diagnosis.

METHODS

A total of 10 HPA patients were enrolled in this study. The coding and adjacent intronic regions of PTS and QDPR genes were examined using Sanger sequencing. Protein modeling was also performed for novel identified variants.

RESULTS

Ten patients and a total of 20 alleles were studied, which led to the identification of 10 different variants. All variants identified in PTS and QDPR were missense, except for the c.383_407del variant in the QDPR. Also, three novel variants were identified in the QDPR, including c.79G>T, c.383_407del and c.488G>A, and a novel variant, c.65C>G, in the PTS.

CONCLUSIONS

Despite the genetic similarities in the disease-causing variants, differences were observed in the Asian and European populations with our populations; As a result, similar but more extensive studies are needed to investigate the distribution of disease-causing variants in genes involved in non-PKU hyperphenylalaninemia.

In silico analysis and the pathogenicity classification of PTS gene variants among Iranian population

Background

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is an autosomal recessive disorder caused by PTS gene mutations. The aim of this study was to collect all PTS gene variants detected among Iranian patients with PTPS deficiency as well as in the Iranome project and classify them based on American College of Medical Genetics and Genomics (ACMG-AMP) guidelines.

Results

The number of PTS gene variants reported among Iranian PTPS patients and in the Iranome project were 19 and 36, respectively. Given that one variant was reported in both of our sources, the total number of variants was 54. These variants were classified as pathogenic (n = 11), likely pathogenic (n = 7), VUS (n = 23), likely benign (n = 1), and benign (n = 12). Out of 19 variants reported among Iranian PTPS patients, c.155A>G (p.Asn52Ser, rs104894275) and c.317C>T (p.Thr106Met, rs200712908) were the most frequent ones, each with a frequency of 10%. c.84-3C>G (rs1230781262) (7.5%) and c.281A>T (p.Asp94Val) (5%) were in the next ranks of the list of variants.

Conclusions

The ACMG-AMP criteria need to be updated depending on the type of disease. In addition, to the best of our knowledge, no template has been described for classifying the variants identified in PTPS deficiency. Therefore, this study can be a good reference for future studies in this subject.

Identification and molecular analysis of 11 cases of the PTS gene variants associated with tetrahydrobiopterin deficiency

Background: Tetrahydrobiopterin deficiency (BH4D) is a rare autosomal recessive amino acid metabolic disease that belongs to a kind of hyperphenylalaninemia (HPA), and 6-pyruvyltetrahydrotrexate synthase (PTPS) deficiency is the most common type of BH4D. This study investigates the clinical and genetic characteristics of 11 PTPS deficiency cases in the Beijing area, identifies the genetic pathogenic factors, and evaluates the value of high-throughput sequencing in the precise diagnosis of PTPS deficiency.

Methods: The Beijing Neonatal Disease Screening Center diagnosed patients with HPA. The study used phenylalanine (Phe) in blood, the ratio of Phe to Thr, urotrexate spectrum analysis, erythrocyte dihydrotrexate reductase (DHPR) activity determination, and high-throughput sequencing as methods. Bioinformatics software analyzed the variants’ pathogenicity and used RT-PCR to identify deep intron variants’ pathogenicity.

Result: Among 635 cases with HPA, 38 cases were diagnosed with BH4D, of which the incidence in HPA was 5.98%. Nine kinds of PTS gene variants were detected, including seven missense variants, one splicing variant, and one deletion variant. The splicing variant c.84–291A>G had three splicing results in vivo: normal length, 79bp pseudoexon insertion, and exon 3 skipping. Bioinformatics and Sanger sequencing were performed to verify the identified variants.

Conclusion: High-throughput sequencing is a helpful tool for clinical diagnosis and differential diagnosis of BH4D. This study confirms that c.84–291A>G is the hot spot variant of PTPS deficiency, and it is the first reported variant with a new splicing pattern in vivo. A novel deletion variant c.84_163del (p.Lys29Cysfs∗9) was found to enrich the genetic variant spectrum of the disease.

Clinical, biochemical and molecular spectrum of mild 6-pyruvoyl-tetrahydropterin synthase deficiency and a case report

Background 6-Pyruvoyl-tetrahydropterin synthase (PTS) is the key enzyme in BH4 synthesis. PTS deficiency is classified as severe type and mild type, and the prognosis and treatment differ for these types. Distinguishing between two types in the early stage is difficult. Reference to reported cases is needed for interpretation of the correlation between genotype and prognosis. Case report: We report a full-term female newborn with mild PTS deficiency. On the day 21 after birth, the phenylalanine level was 859.6 mmol/L (reference range: 30-117 mmol/L). After 1 year of observation, the patient was found to be in a healthy condition without treatment. Conclusions: Although the phenylalanine level is high in mild PTS deficiency patients after birth, some of them may have few symptoms with no treatment. We review 19 cases and find 8 mutations of PTS that may be associated with mild PTS deficiency.

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.

Tetrahydrobiopterin deficiencies: Lesson from clinical experience

OBJECTIVES

The present study describes clinical, biochemical, molecular genetic data, current treatment strategies and follow-up in nine patients with tetrahydrobiopterin (BH4) deficiency due to various inherited genetic defects.

METHODS

We analyzed clinical, biochemical, and molecular data of nine patients with suspected BH4 deficiency. All patients were diagnosed at Ege University Faculty of Medicine in Izmir, Turkey and comprised data collected from 2006 to 2019. The diagnostic laboratory examinations included blood phenylalanine and urinary or plasma pterins, dihydropteridine reductase (DHPR) enzyme activity measurement in dried blood spots, folic acid and monoamine neurotransmitter metabolites in cerebrospinal fluid, as well as DNA sequencing.

RESULTS

Among the nine patients, we identified one with autosomal recessive GTP cyclohydrolase I (ar GTPCH) deficiency, two with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, three with sepiapterin reductase (SR) deficiency, and three with DHPR deficiency. Similar to previous observations, the most common clinical symptoms are developmental delay, intellectual disability, and movement disorders. All patients received treatment with l-dopa and 5-hydroxytryptophan, while only the ar GTPCH, the PTPS, and one DHPR deficient patients were supplemented in addition with BH4. The recommended dose range varies among patients and depends on the type of disease. The consequences of BH4 deficiencies are quite variable; however, early diagnosis and treatment will improve outcomes.

CONCLUSIONS

As BH4 deficiencies are rare group of treatable neurometabolic disorders, it is essential to diagnose the underlying (genetic) defect in newborns with hyperphenylalaninemia. Irreversible brain damage and progressive neurological deterioration may occur in untreated or late diagnosed patients. Prognosis could be satisfying in the cases with early diagnose and treatment.

BH4-deficient hyperphenylalaninemia in Russia

A timely detection of patients with tetrahydrobiopterin (BH₄) -deficient types of hyperphenylalaninemia (HPABH₄) is important for assignment of correct therapy, allowing to avoid complications. Often HPABH₄ patients receive the same therapy as phenylalanine hydroxylase (PAH) -deficiency (phenylketonuria) patients—dietary treatment—and do not receive substitutive BH₄ therapy until the diagnosis is confirmed by molecular genetic means. In this study, we present a cohort of 30 Russian patients with HPABH₄ with detected variants in genes causing different types of HPA. Family diagnostics and biochemical urinary pterin spectrum analyses were carried out. HPABH₄A is shown to be the prevalent type, 83.3% of all HPABH₄ cases. The mutation spectrum for the PTS gene was defined, the most common variants in Russia were p.Thr106Met—32%, p.Asn72Lys—20%, p.Arg9His—8%, p.Ser32Gly—6%. We also detected 7 novel PTS variants and 3 novel QDPR variants. HPABH₄ prevalence was estimated to be 0.5–0.9% of all HPA cases in Russia, which is significantly lower than in European countries on average, China, and Saudi Arabia. The results of this research show the necessity of introducing differential diagnostics for HPABH₄ into neonatal screening practice.

Parkinsonism in children: Clinical classification and etiological spectrum

Infantile- and childhood-onset parkinsonism is mainly due to genetic alterations and is an exceedingly rare condition, unlike Parkinson's disease (PD), which is one of the most common neurologic disorders in adulthood. The clinical characterization of parkinsonism during early stages of neuromotor development is controversial due to the lack of consensus regarding the clinical criteria of PD or parkinsonism in the immature brain. The classification here proposed is based on a review of conditions that emerge during infancy and childhood, with key symptoms evocative of adult parkinsonism. The proposed nosography is based on age at presentation, clinical features, outcome, and etiological background. It includes developmental parkinsonism, infantile degenerative parkinsonism, parkinsonism in the setting of neurodevelopmental disorders, parkinsonism in the setting of multisystem brain diseases, juvenile parkinsonism and dystonia-parkinsonism, and acquired parkinsonism. The subgroups denoting peculiar clinical presentations as a consequence of disease impact on the immature brain are developmental parkinsonism due to monoamine metabolic disorders and infantile degenerative parkinsonism caused by DAT and WASR2 defects. More tardive parkinsonisms occur in genetic conditions that cause a generalized derangement of neurodevelopmental processes, such as those due to MECP2, NR4A2, SCN1A, and RAB39B. Some conditions presenting with neurodevelopmental disorder can progress later, disclosing their neurodegenerative nature (i.e. WDR45 and KCND3). Finally, new emerging conditions with childhood-onset parkinsonism arise from the cumulative effect of multiple genetic lesions.

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.

Consensus guideline for the diagnosis and treatment of tetrahydrobiopterin (BH4) deficiencies

BACKGROUND

Tetrahydrobiopterin (BH4) deficiencies comprise a group of six rare neurometabolic disorders characterized by insufficient synthesis of the monoamine neurotransmitters dopamine and serotonin due to a disturbance of BH4 biosynthesis or recycling. Hyperphenylalaninemia (HPA) is the first diagnostic hallmark for most BH4 deficiencies, apart from autosomal dominant guanosine triphosphate cyclohydrolase I deficiency and sepiapterin reductase deficiency. Early supplementation of neurotransmitter precursors and where appropriate, treatment of HPA results in significant improvement of motor and cognitive function. Management approaches differ across the world and therefore these guidelines have been developed aiming to harmonize and optimize patient care. Representatives of the International Working Group on Neurotransmitter related Disorders (iNTD) developed the guidelines according to the SIGN (Scottish Intercollegiate Guidelines Network) methodology by evaluating all available evidence for the diagnosis and treatment of BH4 deficiencies.

CONCLUSION

Although the total body of evidence in the literature was mainly rated as low or very low, these consensus guidelines will help to harmonize clinical practice and to standardize and improve care for BH4 deficient patients.

The study of the full spectrum of variants leading to hyperphenylalaninemia have revealed 10 new variants in the PAH gene

This study presents further research into the spectrum of variants in genes responsible for the development of phenylketonuria (PKU) and hyperphenylalaninemia (HPA) in patients in Russia. After a study of 25 frequent variants, 293 patients (327 chromosomes without detected variants) from among 1265 probands still had no confirmed diagnosis. A study involving methods of next generation sequencing (NGS) of PAH, PTS, GCH1, PCBD1, QDPR, SPR and DNAJC12 genes to search for point mutations and multiplex ligation-dependent probe amplification (MLPA) methods to search for gross deletions were conducted for these patients. Among 327 chromosomes without identified variants, variants in the PAH gene were found on 260 chromosomes, and variants in the PTS gene were found on 10 chromosomes. On 10 chromosomes gross deletions by the MLPA method were detected. 104 rare variants of the РАН gene, including 10 variants not previously described, and 6 variants of the PTS gene were revealed. The NGS method revealed additional РАН gene variants on 10.3% of chromosomes and PTS gene variants on 0.4%. Gross deletions of the РАН gene were revealed in 0.5% of chromosomes. Thus, the most complete understanding of the spectrum of variants leading to the development of the PKU and HPA in Russia with the use of all methods available today has been obtained. Such a detailed study of the spectrum of rare variants on the genetic material from Russia was undertaken for the first time.

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.

BH4 deficiency identified in a neonatal screening program for hyperphenylalaninemia

OBJECTIVES

To show the general prevalence and to characterize tetrahydrobiopterin (BH₄) deficiencies with hyperphenylalaninemia, identified by the Neonatal Screening Program of the State of Minas Gerais.

METHODS

Descriptive study of patients with BH₄ deficiency identified by the Neonatal Screening Program of the State of Minas Gerais.

RESULTS

The prevalence found was 2.1 for 1,000,000 live births, with a frequency of 1.71% among hyperphenylalaninemias. There were four cases (40%) with 6-pyruvoyl-tetrahydropterin synthase deficiency, three with GTP cyclohydrolase I - autosomal recessive form deficiency, and three with dihydropteridine reductase deficiency (30% each). Six patients were diagnosed due to clinical suspicion and four cases due to systematic screening in neonatal screening. After the start of the treatment, patients identified by neonatal screening had rapid improvement and improved neuropsychomotor development compared to those diagnosed by the medical history.

CONCLUSIONS

The prevalence of BH₄ deficiencies in Minas Gerais was slightly higher than that found in the literature, but the frequency among hyperphenylalaninemias was similar. Although rare, they are severe diseases and, if left untreated, lead to developmental delays, abnormal movements, seizures, and premature death. Early treatment onset (starting before 5 months of age) showed good results in preventing intellectual disability, justifying the screening of these deficiencies in newborns with hyperphenylalaninemia identified at the neonatal screening programs for phenylketonuria.

Inherited metabolic diseases in the Southern Chinese population: spectrum of diseases and estimated incidence from recurrent mutations

Inherited metabolic diseases (IMDs) are a large group of rare genetic diseases. The spectrum and incidences of IMDs differ among populations, which has been well characterised in Caucasians but much less so in Chinese. In a setting of a University Hospital Metabolic Clinic in Hong Kong, over 100 patients with IMDs have been seen during a period of 13 years (from 1997 to 2010). The data were used to define the spectrum of diseases in the Southern Chinese population. Comparison with other populations revealed a unique spectrum of common IMDs. Furthermore, the incidence of the common IMDs was estimated by using population carrier frequencies of known recurrent mutations. Locally common diseases (their estimated incidence) include (1) glutaric aciduria type 1 (∼1/60,000), (2) multiple carboxylase deficiency (∼1/60,000), (3) primary carnitine deficiency (∼1/60,000), (4) carnitine-acylcarnitine translocase deficiency (∼1/60,000), (5) glutaric aciduria type 2 (∼1/22,500), (6) citrin deficiency (∼1/17,000), (7) tetrahydrobiopterin-deficient hyperphenylalaninaemia due to 6-pyruvoyl-tetrahydropterin synthase deficiency (∼1/60,000), (8) glycogen storage disease type 1 (∼1/150,000). In addition, ornithine carbamoyltransferase deficiency and X-linked adrenoleukodystrophy are common X-linked diseases. Findings of the disease spectrum and treatment outcome are summarised here which may be useful for clinical practice. In addition, data will also be useful for policy makers in planning of newborn screening programs and resource allocation.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.

Disorders of BH4 metabolism and the treatment of patients with 6-pyruvoyl-tetrahydropterin synthase deficiency in Taiwan

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is the most frequent form of tetrahydrobiopterin (BH4) deficiency related to hyperphenylalaninemia (HPA). PTPS deficiency may not only cause a typical phenylketonuric phenotype, but is also accompanied by various neurological signs and symptoms due to impaired synthesis of catecholamines and serotonin. The treatment of PTPS deficiency is aimed at normalizing phenylalanine levels and brain neurotransmitters. The BH4 can be administered to normalize phenylalanine (PHE) levels easily, but, owing to severe side effects, the neurotransmitters, L-DOPA and 5-hydroxytryptophan, should be administered for these patients very carefully. However, optimal dosage of the neurotransmitters for PTPS deficiency patients is difficult to be determined. Several reports have described unsatisfied outcomes in a large percentage of patients with PTPS deficiency, despite early detection and treatment. Between 1988 and 2000, 12 newborns with PTPS deficiency identified by newborn screening were referred and received early treatment at our hospital. The mean IQ score of these 12 patients was 96.7 (±9.7; range: 86-119), which is considerably higher than previous reports of other populations of PTPS-deficient patients. In this report, we reviewed the disorders of BH4 briefly and then described treatments of our PTPS-deficient patients.

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Dopa-responsive dystonia

Clinical characteristics and pahophysiologies of dopa-responsive dystonia are discussed by reviewing autosomal-dominant GTP cyclohydrolase-I deficiency (AD GCHI D), recessive deficiencies of enzymes of pteridine metabolism, and recessive tyrosine hydroxylase (TH). Pteridine and TH metabolism involve TH activities in the terminals of the nigrostriatal dopamine neuron which show high in early childhood and decrease exponentially with age, attaining stational low levels by the early 20s. In these disorders, TH in the terminals follows this course with low levels and develops particular symptoms with functional maturation of the downstream structures of the basal ganglia; postural dystonia through the direct pathway and descending output matured earlier in early childhood and parkinsonism in TH deficiency in teens through the D2 indirect pathway ascending output matured later. In action-type AD GCHI D, deficiency of TH in the terminal on the subthalamic nucleus develops action dystonia through the descending output in childhood, focal and segmental dystonia and parkinsonism in adolescence and adulthood through the ascending pathway maturing later. Dysfunction of dopamine in the terminals does not cause degenerative changes or higher cortical dysfunction. In recessive disorders, hypofunction of serotonin and noradrenaline induces hypofunction of the dopamine in the perikaryon and shows cortical dysfunction.

Disorders of biopterin metabolism

Defects in the metabolism or regeneration of tetrahydrobiopterin (BH4) were initially discovered in patients with hyperphenylalaninaemia who had progressive neurological deterioration despite optimal metabolic control (malignant hyperphenylalaninaemia). BH4 is an essential cofactor not only for phenylalanine hydroxylase, but also for tyrosine and two tryptophan hydroxylases, three nitric oxide synthases, and glyceryl-ether monooxygenase. Defective activity of tyrosine and tryptophan hydroxylases explains the neurological deterioration in patients with BH4 deficiency with progressive mental and physical retardation, central hypotonia and peripheral spasticity, seizures and microcephaly. Five separate genetic conditions affect BH4 synthesis or regeneration: deficiency of GTP cyclohydrolase I, 6-pyruvoyl tetrahydropterin synthase, sepiapterin reductase, dihydropteridine reductase (DHPR) and pterin-4alpha-carbinolamine dehydratase. Only the latter of these conditions is relatively benign and is associated with transient hyperphenylalaninaemia. All these conditions can be identified in newborns by an elevated phenylalanine, with the exception of sepiapterin reductase and the dominant form of GTP cyclohydrolase I deficiency that results in biopterin deficiency/insufficiency only in the brain. Diagnosis relies on the measurement of pterin metabolites in urine, dihydropteridine reductase in blood spots, neurotransmitters and pterins in the CSF and on the demonstration of reduced enzyme activity (red blood cells or fibroblasts) or causative mutations in the relative genes. The outcome of BH4 deficiency is no longer malignant if therapy is promptly initiated to reduce plasma phenylalanine levels and replace missing neurotransmitters. This is accomplished by a special diet and/or BH4 supplements and administration of L-dopa, carbidopa, 5-hydroxytryptophan, and, in certain cases, a MAO-B inhibitor. Patients with DHPR deficiency also require folinic acid supplements, since DHPR may help in maintaining folate in the tetrahydro form. Several patients with BH4 deficiency treated since the newborn period have reached adult age with good outcome.

Tetrahydrobiopterin deficiency in human rabies

Rabies is a fatal viral encephalitis characterized by a clinically acute and progressive course. With rare exceptions, there is a discrepancy between clinical outcome and frank histological alterations in rabies. Investigators have postulated that rabies virus may modify neurotransmission through occupancy of cellular receptors or alteration of ion channels. We took advantage of these observations to improvise a successful therapy for rabies. The Milwaukee protocol ( www.mcw.edu/rabies ) was further modified to treat two German patients. We measured pterins and monoamine neurotransmitter metabolites in the CSF of patients with rabies by HPLC with electrochemical or fluorescent detection. We report loss of tetrahydrobiopterin (BH(4)) and associated pathological decrease of dopaminergic and serotoninergic neurotransmission in three successive patients with rabies. CSF levels of BH(4) and neurotransmitter metabolites increased in two patients who were supplemented. Our findings support the long-standing speculation of modified neurotransmission in the pathogenesis of rabies, but by another mechanism. Brain turnover of dopamine and serotonin is reduced following rabies-acquired BH(4) deficiency. Neuronal nitric oxide synthase is BH(4)-dependent and may also be involved, possibly causing cerebrovascular insufficiency in one patient. This work must be carefully replicated in animal models and future patients. We are cautiously optimistic at the prospect of readily available, metabolically specific, enteral therapy for rabies.

Phenotypic variability, neurological outcome and genetics background of 6-pyruvoyl-tetrahydropterin synthase deficiency

This study aimed to investigate the clinical variability and factors implied in the outcome of 6-pyruvoyl-tetrahydropterin synthase deficiency (PTPSd). Biochemical and clinical phenotype, treatment variables, and 6-pyruvoyl-tetrahydropterin synthase (PTS) genotype, were explored retrospectively in 19 Italian patients (12 males and 7 females, aged 4 months to 33 years). According to the level of biogenic amines in cerebrospinal fluid (CSF) at the diagnosis, the patients were classified as mild (6) (normal level) or severe (13) (abnormal low level) form (MF and SF, respectively). Blood Phe ranged from 151 to 1053 micromol/l in MF (mean +/- SD: 698 +/- 403) and 342-2120 micromol/l in SF (mean +/- SD: 1175 +/- 517) (p = 0.063). Patients with MF showed a normal neurological development (a transient dystonia was detected in one), while all SF patients except one presented with severe neurological impairment and only four had a normal neurological development. The outcome of the SF was influenced by the precocity of the treatment. Serial CSF examinations revealed a decline of 5-hydroxyindolacetic acid in MFs and an incomplete restoration of neurotransmitters in SFs: neither obviously affected the prognosis. PTS gene analysis detected 17 different mutations (seven so far unreported) (only one affected allele was identified in three subjects). A good correlation was found between genotype and clinical and biochemical phenotype. The occurrence of brain neurotransmitter deficiency and its early correction (by the therapy) are the main prognostic factors in PTPSd.

Outcome and long-term follow-up of 36 patients with tetrahydrobiopterin deficiency

We describe the treatment, the clinical, and biochemical findings and the outcome of 26 patients with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency and 10 patients with dihydropteridine reductase (DHPR) deficiency. These are the two most common forms of the autosomal-recessively inherited tetrahydrobiopterin (BH4) deficiency. Time of diagnosis, dosage of BH4 and neurotransmitter precursors, folinic acid substitution, and levels of 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA) in cerebrospinal fluid (CSF) are essential parameters in the follow-up of patients. Unfortunately, treatment protocols vary greatly among patients and clinical centers, and CSF investigations and outcome assessments are not always available. Seventeen patients with PTPS deficiency and four patients with DHPR deficiency were diagnosed within 2 months after birth. In 14 patients with PTPS deficiency (54%; 9 early and 5 late diagnosed) and 2 patients with DHPR deficiency (20%; all early diagnosed) no developmental delay is observed, while in 10 patients with PTPS deficiency (38%; 6 early and 4 late diagnosed) and 8 patients with DHPR deficiency (80%; 2 early and 6 late diagnosed) development was delayed. Two PTPS-deficient patients died in the newborn period. DHPR deficiency seems to be more severe than PTPS deficiency and it is clearly the onset of treatment that determines the outcome. Our data suggest that diagnosis within the first month of life is essential for a good outcome and that low CSF5 HIAA and HVA values in CSF could be an indicator for the ongoing developmental impairment

Long-term follow-up and adult outcome of 6-pyruvoyl-tetrahydropterin synthase deficiency

Little information is available on the long-term course and adult outcome of patients with 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. We describe the course of a 32-year-old woman with hypotonia, dystonia, choreoathetosis, mental retardation, behavioral disturbances, and incomplete puberty due to PTPS deficiency. From the age of 6 months she developed progressive hypotonia and choreoathtetoid movements despite good control of hyperphenylalaninemia. Tetrahydrobiopterin deficiency was diagnosed at age 3 years. She had a dramatic response to L-dopa, which persisted at a stable dose for 29 years. Reducing the L-dopa dose led to severe axial hypotonia and limb dystonia, and increasing it led to florid abnormal movements and behavioral disorders. This report illustrates the role of dopamine modulation in motor, psychiatric, and endocrine functions.

6-pyruvoyl-tetrahydropterin synthase deficiency with mild hyperphenylalaninemia

Severe 6-pyruvoyl-tetrahydrobiopterin synthase deficiency is a tetrahydrobiopterin deficiency disorder that presents in infancy with developmental delay, seizures, and abnormal movements associated with hyperphenylalaninemia usually detectable by neonatal phenylketonuria screening programs. We describe an 8-year-old girl with delay, seizures, and dystonia with mild hyperphenylalaninemia detected in late childhood. The diagnosis of 6-pyruvoyl-tetrahydrobiopterin synthase deficiency was made by analysis of pterins in urine, pterins and neurotransmitters in cerebrospinal fluid, and enzyme assay. The patient improved clinically taking oral tetrahydrobiopterin, levodopa/carbidopa, and 5-hydroxytryptophan. This treatable condition may not always be detected by routine population screening for hyperphenylalaninemia.

Diagnosis and treatment of neurotransmitter-related disorders

Neurotransmitter disorders constitute a spectrum of neurologic conditions that share several clinical features depending on the severity and pattern of neurotransmitter deficiency or excess. These uncommon conditions can be suspected based on their clinical features, and several can be confirmed by cerebrospinal fluid analysis of neurotransmitters and their metabolites. Certain disorders, such as autosomal dominant dopa-responsive dystonia caused by GTP cyclohydrolase deficiency, or Segawa syndrome, respond dramatically to medical therapy. This article summarizes current knowledge regarding the clinical manifestations, diagnosis, and treatment of these important disorders.