Psychiatric Manifestations in Patients with Biopterin Defects

Psychiatric manifestations in patients with tetrahydrobiopterin (BH4) defects are common, and may occur even with treatment of the underlying disorder. The neurobiological background of these conditions has been linked to abnormalities of neurotransmitters, such as dopamine, serotonin, norepinephrine, and gamma-aminobutyric acid. Here, we review the psychiatric profile of all patients with BH4 defects followed in the pediatric and adult metabolic clinics at our center. Three patients with autosomal recessive (AR) guanosine triphosphate cyclohydrolase (GTPCH) deficiency and three patients with 6-pyruvoyl tetrahydropterin synthase (PTPS) deficiency were reviewed.All patients had behavioral disturbances and two had significant psychiatric comorbidities. These included attention deficit/hyperactivity disorder, anxiety, depression, aggression, or oppositional defiant disorder. One patient with PTPS deficiency had a severe psychiatric presentation, requiring inpatient admission and temporary placement into foster care for intensive behavioral therapy. Another with AR GTPCH deficiency was diagnosed with aggressive behavioral dysregulation requiring intensive psychiatric treatment. Management of the psychiatric manifestations of BH4 defects can be challenging, due to lack of information and studies of interactions between psychiatric medications on the deficient neurotransmitters and their receptors in these conditions. Further studies are needed to establish safety and efficacy of these treatments.

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.

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.

[Characteristics of gene variants among patients with hyperphenylalaninemia from Quanzhou region of Fujian province]

OBJECTIVE

To explore the spectrum of genetic variants among patients with hyperphenylalaninemia (HPA) from Quanzhou area of Fujian province.

METHODS

For 63 children affected with HPA, next generation sequencing was used to identify potential variants in PAH, PTS, PCBD1, QDPR, SPR and GCH1 genes.

RESULTS

Fifty two variants underlying phenylalanine hydroxylase deficiency (PAHD) and 13 variants underlying 6-pyruvoyl tetrahydropterin synthase deficiency (PTPSD) were identified. Two patients carried variants of both PAH and PTS genes. The most common variants of the PAH gene were R53H (21.69%), R241C(18.07%), R243Q(12.05%) and EX6-96A to G (7.23%), which were mainly located in exons 7 (32.53%), 2 (21.69%), 6 (9.64%) and 12 (9.64%). The L227M variant of the PAH gene was unreported previously. N52S (35.00%), P87S (25.00%), IVS1-291A to G (10.00%) and T67M (10.00%) variants were the most common variants for the PTS gene and were mainly located in exons 2 (35.00%) and 5 (35.00%).

CONCLUSION

The variant spectrum underlying HPA in Quanzhou area showed a geographical specificity. A novel variant of the PAH gene (L227M) has been detected.

Application of isoxanthopterin as a new pterin marker in the differential diagnosis of hyperphenylalaninemia

BACKGROUND

This study aimed to explore the value of applying a new pterin marker (isoxanthopterin) to the traditional urine pterin analysis to reduce the rate of mis-diagnosis of 6-pyruvoyltetrahydropterin synthase deficiency (PTPSD) and improve the accuracy of diagnosis.

METHODS

We compared the urine neopterin (N), biopterin (B), isoxanthopterin (Iso), B% and Iso% levels between patients with phenylalanine hydroxylase deficiency and those with PTPSD, and found the most specific pterin biomarkers by ROC analysis. A positive cut-off value of urine pterins was determined. The effect of combined Iso% + B + B% in reducing PTPSD mis-diagnosis was evaluated, and the different urine pterin levels in PTPSD and false PTPSD (FPTPSD) were compared. The concordance of PTPSD diagnosis by the new pterin scheme and gene mutation analysis was determined.

RESULTS

(1) Urinary B, B%, Iso and Iso% were significantly lower in PTPSD than those in phenylalanine hydroxylase-deficiency group (P < 0.01); (2) Iso%, B%, and B were the most specific markers; (3) The positive cut-off values of B, B%, Iso% for PTPSD were < 0.17 mmoL/moLCr, < 5.0%, and < 9.5%, respectively; (4) urinary B + B% + Iso% scheme significantly reduced the false-positive rate of PTPSD compared to traditional ones. The Iso% levels in FPTPSD group were higher than the ones in PTPSD group; (5) an accuracy of diagnosis for PTPSD was increased by 9-19% when Iso% was introduced to urinary pterin scheme.

CONCLUSIONS

Iso% is helpful to reduce the rate of misdiagnosis of PTPSD in the diagnosis by urinary pterin analysis for hyperphenylalaninemias and improve the accuracy of diagnosis. This approach is worthy of further development and increased utilization.

Tetrahydrobiopterin in antenatal brain hypoxia-ischemia-induced motor impairments and cerebral palsy

Antenatal brain hypoxia-ischemia, which occurs in cerebral palsy, is considered a significant cause of motor impairments in children. The mechanisms by which antenatal hypoxia-ischemia causes brain injury and motor deficits still need to be elucidated. Tetrahydrobiopterin is an important enzyme cofactor that is necessary to produce neurotransmitters and to maintain the redox status of the brain. A genetic deficiency of this cofactor from mutations of biosynthetic or recycling enzymes is a well-recognized factor in the development of childhood neurological disorders characterized by motor impairments, developmental delay, and encephalopathy. Experimental hypoxia-ischemia causes a decline in the availability of tetrahydrobiopterin in the immature brain. This decline coincides with the loss of brain function, suggesting this occurrence contributes to neuronal dysfunction and motor impairments. One possible mechanism linking tetrahydrobiopterin deficiency, hypoxia-ischemia, and neuronal injury is oxidative injury. Evidence of the central role of the developmental biology of tetrahydrobiopterin in response to hypoxic ischemic brain injury, especially the development of motor deficits, is discussed.

[PTPS gene analysis and prenatal diagnosis in patients with 6-pyruvoyl-tetra hydropterin synthase deficiency]

Objective: To analyze the variations of PTPS gene in patients with suspected 6-pyruvoyl-tetra hydropterin synthase deficiency (PTPSD) and to make prenatal diagnosis in high-risk families. Methods: Chemiluminescence was used for phenylalanine detection in blood or dried blood spots.Patients with phenylalanine concentration over 120 μmol/L were detected by urine pterin analysis, and the activity of dihydropteridine reductase (DHPR) was detected. tetrahydrobiopterin loading tests were performed in suspected patients with abnormal urinary pterin profiles. PTPS gene variation analysis was performed by direct Sanger sequencing based on PCR amplification. Prenatal diagnosis in 7 high-risk families was performed by chorionic villus sampling when the genotype was identified. Results: In 656 patients with hyperphenylalanine, 22 cases were diagnosed as PTPSD clinically. 16 variations were detected in the 22 PTPSD cases. The 5 variations, p.Lys77Arg, p.Ile84Phe, c.315-2A>G, c.244-2A>T, c.187-1G>T, were identified as novel variations. Two fetuses carried the same mutation with the proband and therefore were thought to be PTPSD fetuses. Three fetuses carried only one mutant allele and thus were thought to be PTPSD carriers. The other 2 fetuses carried no mutations and were presumed normal. Conclusions: PTPS gene variation analysis is necessary to confirm the diagnosis. Prenatal diagnosis could help avoiding the defect birth in PTPSD families.

Demographics, diagnosis and treatment of 256 patients with tetrahydrobiopterin deficiency in mainland China: results of a retrospective, multicentre study

BACKGROUND

National coverage of neonatal screening for hyperphenylalaninaemia (HPA) in China is still low and tests to differentiate causes of HPA are not performed in many centres. This study aimed to describe the demographics, geographic distribution, diagnosis, treatment and clinical outcomes of treatment, including intellectual development, in patients with tetrahydrobiopterin (BH4) deficiency in mainland China.

METHODS

This was a retrospective, multicentre, chart review in patients with BH4 deficiency across mainland China born 1985-2010.

RESULTS

Two hundred fifty six patients were included; 59.9 % (267/446) of parents were from eastern China. Median (interquartile range) age at diagnosis decreased from 12.0 (5.5, 102.0) months to 2.0 (1.0, 3.5) months in patients born 1985-1999 (n = 28) and 2005-2010 (n = 152), respectively. 6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency was the primary cause of BH4 deficiency (96.0 %); four hotspot mutations accounted for 76.6 % of PTS gene mutations; two novel variants in the QDPR gene were identified. Most patients (83.6 %) received treatment with BH4, L-dopa, 5-hydroxytryptophan and/or diet therapy. Target blood Phe concentration was confirmed at 88.9 % of visits; median (Q1, Q3) blood Phe concentration was 106.8 (73.0, 120.0) μmol/L during therapy and 117.0 (67.1, 120.0) μmol/L at last visit. Median (Q1, Q3) WISC IQ score was 80.0 (69.0, 90.0) in 33 patients. DQ scores were within normal range (≥85) for 37/59 (62.7 %) patients. Physical development indicators were within normal ranges. Treatment-related adverse events, reported in 20/256 (7.8 %) patients, were mild-to-moderate in severity.

CONCLUSION

This study provides valuable information on the current and historical situation of BH4 deficiency in mainland China.

An international survey of patients with tetrahydrobiopterin deficiencies presenting with hyperphenylalaninaemia

OBJECTIVES

The present study summarizes clinical and biochemical findings, current treatment strategies and follow-up in patients with tetrahydrobiopterin (BH(4)) deficiencies.

METHODS

We analyzed the clinical, biochemical and treatment data of 626 patients with BH(4) deficiencies [355 with 6-pyruvoyl-tetrahydropterin synthase (PTPS), 217 with dihydropteridine reductase (DHPR), 31 with autosomal recessive GTP cyclohydrolase I (GTPCH), and 23 with pterin-4a-carbinolamine dehydratase (PCD) deficiencies] from the BIODEF Database. Patients with autosomal dominant GTPCH and SR deficiencies will not be discussed in detail.

RESULTS

Up to 57 % of neonates with BH(4) deficiencies are already clinically symptomatic. During infancy and childhood, the predominant symptoms are muscular hypotonia, mental retardation and age-dependent movement disorders, including dystonia. The laboratory diagnosis of BH(4) deficiency is based on a positive newborn screening (NBS) for phenylketonuria (PKU), characteristic profiles of urinary or dried blood spot pterins (biopterin, neopterin, and primapterin), and the measurement of DHPR activity in blood. Some patients with autosomal recessive GTPCH deficiency and all with sepiapterin reductase deficiency may be diagnosed late due to normal blood phenylalanine in NBS. L-dopa, 5-hydroxytryptophan, and BH(4) are supplemented in PTPS and GTPCH-deficient patients, whereas L-dopa, 5-hydroxytryptophan, folinic acid and diet are used in DHPR-deficient patients. Medication doses vary widely among patients, and our understanding of the effects of dopamine agonists and monoamine catabolism inhibitors are limited.

CONCLUSIONS

BH(4) deficiencies are a group of treatable pediatric neurotransmitter disorders that are characterized by motor dysfunction, mental retardation, impaired muscle tone, movement disorders and epileptic seizures. Although the outcomes of BH(4) deficiencies are highly variable, early diagnosis and treatment result in improved outcomes.

Dopamine agonists in dihydropteridine reductase deficiency

The traditional treatment of severe disorders of tetrahydrobiopterin (BH4) metabolism is based on the replacement therapy with BH4, 5-hydroxytryptophan, and L-dopa. Major problems are encountered with L-dopa therapy, especially with increasing age when higher doses are necessary, because of its short half-life and adverse effects. Consequently, different L-dopa-sparing strategies have been successively introduced, with partial reduction of L-dopa dosage and amelioration of the clinical outcome. Recently, we demonstrated that the dopamine agonist pramipexole improves the therapeutic effect of L-dopa in 6-pyruvoyl tetrahydropterin synthase (PTPS) deficiency, the most common disorder of BH4 metabolism. Here we report its effectiveness in two patients (males, 7 and 22 years) with dihydropteridine reductase (DHPR) deficiency, the second most frequent cause of BH4 deficiency. Both patients experienced residual symptoms of dopamine deficiency, movement and behavioral disability, and complications of L-dopa therapy, associated with fluctuating hyperprolactinemia. They had full clinical and biochemical assessment, by an adapted Unified Parkinson's Disease Rating Scale (UPDRS) and measurement of diurnal plasma prolactin (PRL) profile before and after a trial with pramipexole. Besides allowing the reduction of L-dopa daily dosage (-58%) and administrations (from three to two) in one patient and to stop L-dopa therapy in the other, the introduction of pramipexole markedly improved and stabilized clinical and biochemical picture in both patients, as revealed by reduction of UPDRS scores and normalization of diurnal plasma prolactin profiles. Dopamine agonists can improve or even replace L-dopa therapy in disorders of synthesis and regeneration of BH4.

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.

Pseudoexon exclusion by antisense therapy in 6-pyruvoyl-tetrahydropterin synthase deficiency

Antisense oligonucleotide therapy to modulate splicing mutations in inherited diseases is emerging as a treatment option also for metabolic defects. In this article, we report the effect of cellular antisense therapy to suppress pseudoexon activation in primary dermal fibroblasts from patients with mutations in the PTS gene encoding 6-pyruvoyltetrahydropterin synthase (PTPS), which leads to tetrahydrobiopterin and monoamine neurotransmitter deficiency. Pathogenic inclusion of SINE or LINE-derived cryptic exons in different PTPS patients due to the intronic mutations c.84-322A>T, c.163 + 695_163 + 751del57, or c.164-712A>T was demonstrated by transcript analysis in fibroblasts and minigene ex vivo assays. Antisense morpholino oligonucleotides (AMOs) directed to the pseudoexons 3' or 5' splice sites were designed with the aim of preventing the pathological pseudoexon inclusion. At the time of AMO transfection, we investigated patients' cells for correct PTS-mRNA splicing and functional recovery of the PTPS protein. Transcriptional profiling after 24 hr posttransfection revealed a dose- and sequence-specific recovery of normal splicing. Furthermore, PTPS enzyme activity in all three patients' fibroblasts and the pterin profile were close to normal values after antisense treatment. Our results demonstrate proof-of-concept for pseudoexon exclusion therapy using AMO in inherited metabolic disease.

Partial biopterin deficiency disturbs postnatal development of the dopaminergic system in the brain

Postnatal development of dopaminergic system is closely related to the development of psychomotor function. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of dopamine and requires tetrahydrobiopterin (BH4) as a cofactor. To clarify the effect of partial BH4 deficiency on postnatal development of the dopaminergic system, we examined two lines of mutant mice lacking a BH4-biosynthesizing enzyme, including sepiapterin reductase knock-out (Spr(-/-)) mice and genetically rescued 6-pyruvoyltetrahydropterin synthase knock-out (DPS-Pts(-/-)) mice. We found that biopterin contents in the brains of these knock-out mice were moderately decreased from postnatal day 0 (P0) and remained constant up to P21. In contrast, the effects of BH4 deficiency on dopamine and TH protein levels were more manifested during the postnatal development. Both of dopamine and TH protein levels were greatly increased from P0 to P21 in wild-type mice but not in those mutant mice. Serotonin levels in those mutant mice were also severely suppressed after P7. Moreover, striatal TH immunoreactivity in Spr(-/-) mice showed a drop in the late developmental stage, when those mice exhibited hind-limb clasping behavior, a type of motor dysfunction. Our results demonstrate a critical role of biopterin in the augmentation of TH protein in the postnatal period. The developmental manifestation of psychomotor symptoms in BH4 deficiency might be attributable at least partially to high dependence of dopaminergic development on BH4 availability.

Maternal tetrahydrobiopterin deficiency: the course of two pregnancies and follow-up of two children in a mother with 6-pyruvoyl-tetrahydropterin synthase deficiency

No reports are available about the course of pregnancies in women with tetrahydrobiopterin (BH(4)) deficiencies or the effects of treatment with BH(4), L-dopa/carbidopa and 5-hydroxytryptophan (5-OHTrp) on fetal development. We present for the first time the case of a mother with late-diagnosed mild form of 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, the course of her two subsequent pregnancies and clinical evaluation with follow-up of two offspring. In both pregnancies neurotransmitter precursors, as well as BH(4) dosages were increased proportionally to the mother's weight gain. To prevent maternal phenylketonuria (MPKU) syndrome, special attention was paid to increasing BH(4) dosages. Both pregnancies were complicated by threatened premature labour, by the mother's nicotinism and additionally, in the first pregnancy, by gestational diabetes mellitus and vaginitis. The first child was born in the 31st week of pregnancy with the symptoms of moderate intrauterine growth retardation (IUGR) and brain malformation in the form of right sided closed-lip schizencephaly with absence of septum pellucidum. Although the girl demonstrates mild left-sided hemiparesis, her psychological development at the age of 8 years is above average. The second child was born in the 37th week of pregnancy without brain anomalies and at the age of 5 years his psychomotor development is appropriate for the age. As the cause of brain malformations resulting in physical impairment in the first child is unknown, more data are essential to verify conclusions about the influence of the mother's BH(4) deficiency and the safety of her treatment for fetal development.

Novel mutation affecting the pterin-binding site of PTS gene and review of PTS mutations in Thai patients with 6-pyruvoyltetrahydropterin synthase deficiency

Tetrahydrobiopterin (BH(4)) deficiency comprises heterogeneous disorders resulting in hyperphenylalaninaemia (HPA) and lack of monoamine neurotransmitters. Among these, 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is the most common disorder. We report a female Thai patient with PTPS deficiency who was initially detected by newborn screening for HPA, and later treated by supplements of BH(4), L-dopa/carbidopa, and 5-hydroxytryptophan. Monitoring of serum prolactin representing dopamine sufficiency is used for optimizing the dosage of L-dopa. She showed a remarkable progress of development despite delayed treatment at 5 months of age. Mutation analysis revealed two heterozygous missense mutations of the PTS gene: c.259C>T (p.P87S) inherited from the father; and c.147T>G (p.H49Q) inherited from the mother. The latter is a novel mutation that affects the pterin-binding site of the PTPS enzyme. This novel mutation expands the mutation spectrum of PTPS deficiency. Notably, some PTS mutations have been reported in both Thai and Chinese patients. Whether these common mutations are the result of a founder effect with common ancestors of Thai and Chinese people or intermarriage between Thai and Chinese descents in Thailand remain unclear. In conclusion, severe neurological impairment from BH(4) deficiency could be prevented by newborn screening for HPA and proper metabolic management. However, pterin analysis for early diagnosis of BH(4) deficiency is still not available in most developing countries.

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

A case of 6-pyruvoyl-tetrahydropterin synthase deficiency demonstrates a more significant correlation of L-Dopa dosage with serum prolactin levels than CSF homovanillic acid levels

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a tetrahydrobiopterin (BH4) deficiency that presents as hyperphenylalaninemia. Administration of the neurotransmitter precursors L-Dopa/carbidopa and 5-hydroxytryptophan (5HTP), as well as BH4, is necessary for treatment. It has been reported that serum prolactin levels are elevated in patients with PTPS deficiency indicating that inhibition of prolactin secretion by dopamine is insufficient and is negatively correlated with the CSF level of HVA. Here, we present a case of PTPS deficiency which showed a more significant correlation of dosage of L-Dopa/carbidopa with serum prolactin levels than with CSF HVA levels. Combined treatment of BH4, L-Dopa/carbidopa, and 5HTP was started as the CSF neopterin/biopterin ratio (N/B ratio 7.54, control 0.46-1.59) and serum prolactin level (36.79 ng/ml, control <15) were elevated. The dosage of L-Dopa/carbidopa was adjusted in the range of 9.08-10.5mg/kg/day. The CSF level of HVA stayed within normal limits using these dosages of L-Dopa/carbidopa, and there was no correlation between dose given and HVA level (R=0.230, p=0.71). On the other hand, even in this relatively small dosing range, the serum prolactin level showed significant negative correlation with the dosage of L-Dopa/carbidopa (R=0.645, p=0.023). The patient did not show any neurological symptoms even when the serum prolactin level was elevated. From these results, we suggest that the serum prolactin level may be a more sensitive marker than the CSF HVA level to guide the dose adjustment of L-Dopa/carbidopa in the management of patients with PTPS deficiency.

Early initiation of L-dopa therapy enables stable development of executive function in tetrahydrobiopterin (BH4) deficiency

Executive function (EF) has been presumed to be mediated by the dopaminergic system in the prefrontal cortex. However, little is known about the early development of this function and the roles dopamine plays in it. Tetrahydrobiopterin (BH4) deficiencies are genetic disorders affecting catecholamine and serotonin biosynthesis which, if untreated, result in motor and cognitive symptoms including impairment of EF. A comprehensive neuropsychological test battery was administered to six participants with BH4 deficiency (four males, two females, mean Full-scale intelligence quotient [FIQ] 63.8 [SD 14.7]); all were on replacement therapy with L-dopa and BH4, but time of initiation of treatment varied. Age range (median) was 28 days to 41 years (2y 6mo) at initiation of treatment and 10 to 47 years (19y) at follow-up. On non-EF tests, performance agreed with those of IQ-matched controls (four males, two females; mean age 16y 6mo [SD 6mo]; mean FIQ 62.3 [SD 13.4]). On EF tests those who initiated treatment after 2 years 6 months of age performed poorly. In patients with BH4 deficiency, replacement therapy should be started in the first weeks or months of life. Patients diagnosed before the age of 2 years 6 months obtain normal EF, which suggests dopamine may play a critical role in ensuring stable development of EF in early life.

[Detection of the prevalent mutations of 6-pyruvoyl-tetrahydropterin synthase gene by PCR-RFLP analysis in Chinese patients]

OBJECTIVE

To establish a single and rapid method for detecting the prevalent mutations of 6-pyruvoyl-tetrahydropterin synthase (PTPS) gene in Chinese patients with 6-pyruvoyl-tetrahydropterin synthase deficiency (PTPSD).

METHODS

PCR-restriction fragment length polymorphism (PCR-RFLP) was used to detect three prevalent PTPS gene mutations in 4 cases of tetrahydrobiopterin deficiency (BH4D) and their parents, which was performed by the artificial construct restriction site (ACRS). PCR-RFLP included Hpa I digestion for the detection of mutation N52S (155A to G), Hae III for P87S (259C to T) and Eco R I for D96N(286G to A). The mutations of PTPS gene were confirmed by direct sequencing.

RESULTS

The genotypes of 4 PTPS deficient patients were identified: N52S/-, P87S/D96N, N52S/D96N and D96N/-. The result of direct sequencing was coincident with that of PCR-RFLP analysis.

CONCLUSION

(1) The PCR-RFLP analysis formed by ACRS would be a good way for detecting the three prevalent PTPS gene mutations in Chinese patients with PTPSD. (2)The PTPS gene analysis is very important for all patients with hyperphenylalaninemia, which would be useful for early clinical diagnosis and correct treatment of BH4D patients.

6-pyruvoyltetrahydropterin synthase deficiency two-case report

6-Pyruvoyltetrahydropterin Synthase (PTPS) deficiency is the most common cause of hyperphenylalaninemia due to tetrahydrobiopterin deficiency. The presenting symptoms of PTPS deficiency are mental retardation, convulsions, disturbance of tone and posture, drowsiness, irritability, abnormal movements, hypersalivation, and swallowing difficulties(1-3). The authors reported the first two cases of PTPS deficiency in Thailand. Both cases were male infants who showed phenylalanine levels of 25.23 mg/dl and 23.4 mg/dl respectively. The urinary pterins analysis showed low biopterin and high neopterin. The percentage of urinary biopterin was also found to be very low. The mutation analysis of the first case revealed a point mutation of exon 4, a homozygous C to T transition at nucleotide 200 in codon 67 (T67M), and the second case showed a compound heterozygous of exon 4, C to A transition at nucleotide 200, and exon 5, C to T transition at nucleotide 259 of the PTS gene confirming that they had PTPS deficiency. Treatment was started with neurotransmitters and a low phenylalanine diet. Family carriers were detected by means of urinary pterins determination and mutation analysis.

[Study on tetrahydrobiopterin deficiency in Northern Chinese population]

OBJECTIVE

To emphasize early differential diagnosis from patients with hyperphenylalaninemia (HPA) and to evaluate the treatment and long-term outcome of patients with tetrahydrobiopterin synthase (BH4) deficiency in Northern Chinese population.

METHODS

From 1992 to 2005, a total of 618 patients with HPA were diagnosed and/or cared for in our outpatient clinic. Urinary pterin analysis, detection of dihydropteridine reductase (DHPR) activity in blood, and then BH4 loading tests were carried out to differentiate BH4 deficiency in these patients from classical phenylketonuria. BH4 deficient patients were treated with BH4, levodopa and 5-hydroxytryptophane (5-HTP) immediately while the diagnosis was done to disease. Patientso blood phenylalanine levels, psychomotor and intelligence development were followed up.

RESULTS

A total of 38 cases were diagnosed as BH4 deficiency, all of them were revealed as 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency from the extremely decreased urine biopterin, normal DHPR activities and drop down of blood phenylalanine level to normal range within 4 to 8 hours after BH4 loading. The most common manifestations were progressively psychomotor and mental retardation to patients even after taking early dietary treatment. The patients were diagnosed and treated with drugs at the ages of 2.1 months to 13 years. With 4 patients died of pneumonia, 7 patients refused to treatment, only 27 patients were under treatment and followed up. The average full scale development or intelligence quotient (DQ/IQ) of patients who were treated within and after 6 months were 86+/- 10 or 66+/- 7 respectively. Development was not even in different aspects. A significant negative correlation was observed between the level of the DQ and the age of treatment commenced (r was -0.714, P< 0.01). Eleven patients experienced the extrapyramidal movement disorders, 3 of them combined with epilepsy. The extrapyramidal disorders were controlled by administration of levodopa.

CONCLUSION

The differential diagnosis for BH4 deficiency should be carried out in all patients with HPA. PTPS deficiency is the most common form of BH4 deficiency in Northern Chinese population. The long-term outcome of these patients benefits from diagnosis and treatment with BH4, levodopa and 5-HTP as early as possible.

Central tegmental tract involvement in an infant with 6-pyruvoyltetrahydropterin synthetase deficiency

We report the case of an asymptomatic 2-month-old infant with 6-pyruvoyltetrahydropterin synthetase deficiency detected through a neonatal phenylketonuria screening program. MR imaging revealed symmetrical lesions in the central tegmental tract with reduced diffusion, which resolved after treatment. A possible explanation for these lesions is intramyelinic edema resulting from brain insults in utero.

Long-term outcome and neuroradiological findings of 31 patients with 6-pyruvoyltetrahydropterin synthase deficiency

Tetrahydrobiopterin (BH(4)) deficiency is an autosomal recessive disorder caused by enzyme defects in the biosynthesis or recycling of BH(4). Patients with BH(4) deficiency present with severe neurological signs and symptoms and require a different treatment from classical phenylketonuria. During the last 12 years, 31 cases of BH(4) deficiency were identified in our department. They were all classified as 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. They were diagnosed at the ages of 2.5-48 months and treated with BH(4), L-dopa and 5-hydroxytryptophan immediately after diagnosis. The average development quotients (DQ) at diagnosis and after treatment for more than 3 years were 53+/- 16, and 78+/- 15, respectively. A significant negative correlation was observed between the level of the DQ and the age at which treatment was commenced (r = -0.751, p = 0.002). Developmental profiles were uneven. Language, adaptability and at later age mathematics were particularly weak areas. Only two patients achieved a good performance in mathematics. Eleven patients who were treated with drugs from ages of 2.9-48 months had neuroradiological scanning. Computed tomography disclosed calcification in lentiform nuclei in one patient and magnetic resonance imaging disclosed delayed myelination and abnormal high intensity signal in cerebral white matter in all of them. Even though most of abnormalities were reversible, small patchy or spotted areas were still present on these regions after treatment for 10-46 months. In summary, our study supports the substantial efficacy of the current therapeutic approach in PTPS deficiency of normalizing amine neurotransmitters with three drugs as early as possible. For the first time, calcifications could be detected in patients with PTPS deficiency. Abnormalities in white matter on magnetic resonance imaging were not related to clinical manifestations and most were reversible.

Long-term follow-up of Chinese patients who received delayed treatment for 6-pyruvoyl-tetrahydropterin synthase deficiency

OBJECTIVES

6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is the most important type of BH4 deficiency related to hyperphenylalaninemia. 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. Reports of the long-term outcomes of these patients, especially after delayed onset of therapy, are few.

STUDY DESIGN

We reviewed the characteristics of 10 PTPS-deficient patients whose treatment onset with tetrahydrobiopterin, L-DOPA, and hydroxytryptophan had been delayed. The relationships among clinical manifestations, biochemical findings, genotypes, and long-term outcomes were analyzed.

RESULTS

We classified eight patients as having severe forms, and two as having moderate forms of PTPS deficiency. Improvements in neurological status and intelligence/developmental quotient (IQ/DQ) were observed in all patients, up to approximately 15 years of follow-up. One patient began walking and talking after 4 years of treatment. In patients with severe disease, the mean initial IQ/DQ was 45.40 +/- 13.94, and the final full-scale intelligence quotient (FIQ) score was 62.8 +/- 13.06 (p = 0.042), with a mean increment of 17.4 +/- 5.27 over 15.86 +/- 4.85 years of follow-up. Two patients with moderately severe disease had FIQ increases from 75 to 77 and from 76 to 80 points, respectively.

CONCLUSIONS

The administration of neurotransmitters based on clinical response and adverse effects was beneficial in patients whose treatment of PTPS deficiency was delayed. Sustained clinical improvements were observed up to 15 years of follow-up.

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.

Subtle brain dysfunction in treated 6-pyruvoyl-tetrahydropterin synthase deficiency: relationship to motor tasks and neurophysiological tests

6-Pyruvoyl-tetrahydropterin synthase (6PTPS) deficiency is a major cause of biopterin deficiency. 6PTPS patients usually have an elevated serum phenylalanine level, a deficiency of neurotransmitters (serotonin and dopamine), and neurological symptoms, if without treatment. We herein investigated the possibility of neurological dysfunction in early-treated patients. In the study, 12 early-treated 6PTPS patients were studied. Their auditory simple reaction time, movement rhythm variation (MRV), somatosensory evoked potentials to median nerve stimulation, and hand muscle responses to transcranial magnetic stimulation, were measured. MRV is a test of repetitive voluntary movements, and was used with and without auditory cues at 0.3 Hz. The 6PTPS patients had an increased motor threshold but normal motor and sensory central conduction times. They performed very well in simple reactions (6PTPS 208.4+/-16.7 ms, control 200.3+/-11.7 ms, p=0.18), but not in continuous tasks. The continuous performance tests showed that MRV had increased in the 6PTPS patients (with cues: 6PTPS 7.35+/-0.94, control 5.47+/-0.80, p<0.0001; without cues: 6PTPS 9.87+/-1.44, control 6.59+/-0.68, p<0.0001). Without cues, MRV had increased in both the 6PTPS and control groups, but more significantly in the 6PTPS patients (6PTPS 2.51+/-0.97, control 1.25+/-0.42; p=0.0001). Our findings indicate that early-treated 6PTPS patients have subtle neurological dysfunctions. They may not maintain movement rhythm as well as normal subjects, even with external cues. Hence, MRV is a good method to assess motor control.

[An eighteen-year study on phenylketonuria]

A study on phenylketonuria (PKU) has been carried out in China-Japan Friendship Hospital since 1984. The results revealed that: (1) Totally 603 patients with PKU were diagnosed and treated in the hospital from October 1984 to September 2002. Among which 136 cases were identified by neonatal screening and treated within 3 months. One hundred and ninety-five cases were treated when the children were 3-12 months of age. Another 272 PKU children were diagnosed when they were more than 1 year old. All of these late-treated cases had some signs and symptoms of PKU. Mental retardation was found in 467 cases and various patterns of seizures in 119 cases. After treatment with low-phenylalanine diet, the follow-up for early-treated patients revealed that their physical and mental developments were normal. In late-treated patients, abnormal behaviour was significantly improved and their developmental quotient were elevated. Prenatal gene diagnosis of PKU risk foetus in 22 PKU families was successfully performed. (2) Urinary pterins obtained from 369 HPA patients were measured by HPLC. Twenty two patients with BH4 deficiency have been recognized. Six single base mutations were detected in 18 unrelated northern Chinese BH4 deficiency families, and the mutations at nucleotides 259C-->T and 286G-->A were common mutations. Eighteen BH4 deficient patients were treated with BH4, L-dopa and 5-hydroxytryptophan, and the results were satisfactory. (3) The abnormal rate of EEG was high in untreated patients with PKU, mainly showing epileptiform discharges and partly showing background activity abnormality. The most frequent finding was patchy areas of increased signal intensity in white matter on MRI in the brain of PKU patients, while delayed myelination and brain agenesis were often detected. After dietary treatment, follow-ups with EEG and MRI revealed that the abnormalities were decreased significantly. (4) The relationship between genotype and intellectual phenotype was examined in 29 late-treated patients with classical PKU. It was found that the genotype of 22 patients were compatible with intellectual phenotype and not well matched in 7 cases. The result indicate that the genotype was well matched with intellectual phenotype in classical PKU patients.

6-pyruvoyl tetrahydropterin synthase deficiency: a case report

A 5 day old girl screened positive for hyperphenylalaninemia on routine newborn screening. Initial diagnostic work-up showed elevated blood phenylalanine of 1100 mmol/L and low tyrosine. Limited protein diet and phenylalanine-free formula were prescribed. Further investigation revealed a defect in biopterin metabolism. Urine had no detectable biopterin (BH4) and an elevated level of neopterin at 24.31 mmol/mole Cr. Enzymatic assay showed zero level of 6-pyruvoyl tetrahydropterin synthase. The activity in the mother was 3.5 or 19.9% of controls consistent with heterozygosity. The concentrations of 5-hydroxyindoleacetic acid and homovanillic acid in the cerebrospinal fluid were below the reference ranges. A treatment regimen of BH4 tablets, 5 hydroxytryptophan and DOPA was initiated. The diagnostic evaluation, management and follow-up of patients with this disorder will be outlined. This is the first reported case of a Filipino with a defect in biopterin metabolism.

Comparative potencies of induction of point mutations and genetic duplications by the methylating agents methylazoxymethanol and dimethyl sulfate in bacteria

Methylazoxymethanol (MAM) and dimethyl sulfate (DMS) are mutagens whose genetic effects can be ascribed to the methylation of DNA. While both methylate the N7 position of guanine heavily, only MAM strongly methylates the O(6) position of guanine. We evaluated the relative effectiveness and specificity of MAM and DMS in bacterial assays for the induction of point mutations and the formation of chromosomal duplications by genetic recombination. Salmonella typhimurium strain TS1121 was used to measure the formation of genetic duplications on the basis of the aroC321 allele and mutations by reversion of the hisG46 allele. Specific base pair substitutions and frameshift mutations were measured in a reversion assay based on lacZ alleles of Escherichia coli. The results show MAM to be the more potent mutagen and DMS the stronger recombinagen in the Salmonella assay. In the lacZ assay DMS induced several classes of base pair substitutions (GC-->AT transitions, GC-->TA transversions and AT-->TA transversions), as well as lower frequencies of +1, -1 and -2 frameshift mutations. The activity of MAM as a base pair substitution mutagen was more specific than that of DMS, inducing only GC-->AT transitions. It also induced +G, -G, -A and -CG frameshift mutations, though more weakly than it induced GC-->AT transitions. Long known as a base pair substitution mutagen, the induction of frameshifts by MAM was unexpected. The results show that both DMS and MAM are effective inducers of base pair substitutions and modest inducers of frameshifts and that DMS exhibits a broader spectrum of mutagenic activity than does MAM.

[Screening of tetrahydrobiopterin deficiency among hyperphenylalaninemic patients]

Tetrahydrobiopterin deficiency in hyperphenylalaninemic babies has to be rapidly recognized since the disease requires a specific follow-up. Based on specimen collection on filter paper, a simple strategy for the screening of this condition has been used since 1987. Urine pteridine measurement can detect 6-pyruvoyl-tetrahydropterin synthase, GTPcyclohydrolase I and pterin-4a-carbinolamine dehydratase deficiencies and direct enzyme measurement in dried blood sample detects dihydropteridine-reductase deficiency. A total of 1,814 hyperphenylalaninemic patients have been studied and 34 tetrahydrobiopterin deficiencies have been detected. The strategy must commend itself by its convenience and simplicity, and can be use on all babies with hyperphenylalaninemia screened in the neonatal period, whatever their blood phenylalanine level.

Reduced nitric oxide metabolites in CSF of patients with tetrahydrobiopterin deficiency

We investigated CSF concentrations of nitrite and nitrate as indicators of nitric oxide (NO) production in patients with tetrahydrobiopterin (BH4) deficiencies. Patients with 6-pyruvoyl-tetrahydropterin synthase, sepiapterin reductase and dihydropteridine reductase deficiencies exhibited decreased CSF nitrite + nitrate levels compared with healthy control subjects. Reduced levels of nitrite + nitrate were not influenced by oral administration of 2.5-5.0 mg/kg tetrahydrobiopterin. Our data indicate impaired NO synthase function in patients with BH4 deficiency and suggest possible involvement in the neuronal cell dysfunction.

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

The outcome of 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency, the most common form of tetrahydrobiopterin (BH4) deficiency, depends on factors such as severity of the disease, type of mutation, time of diagnosis, and mode of treatment. We investigated five patients from four different families, four of them presenting with the severe form of PTPS deficiency and one with the mild peripheral form. In this study, missense (L26F, T67M, P87L, V124L, D136G, D136V) and nonsense (R15-16ins) mutations were detected by reverse transcriptase polymerase chain reaction and sequence analysis. Two patients with the severe form were compound heterozygotes (T67M/P87L and D136G/R15-16ins), two siblings were homozygous for the D136V mutation, and in the patient with the mild form, heterozygous L26F/V124L mutations were present. Two patients are on combined therapy with L-dopa/carbidopa/5-hydroxytryptophan plus BH4, the siblings are on monotherapy with BH4, and the patient with the mild form is now off treatment, presenting with normal plasma phenylalanine levels.

CONCLUSION

Long-term follow-up shows that the outcome of 6-pyruvoyl-tetrahydropterin synthase deficiency benefits from treatment started in the first months of life and that the phenotype may change with age. Additionally, depending on the type of mutations, prenatal damage to the fetus may multiply the clinical abnormalities and thus worsen the prognosis of the disease. In patients initially diagnosed with the mild peripheral form of the disease, therapy with tetrahydrobiopterin should be stopped after some time to test whether hyperphenylalaninaemia was only a transient condition.

Identification of three novel 6-pyruvoyl-tetrahydropterin synthase gene mutations (226C>T, IVS3+1G>A, 116-119delTGTT) in Chinese hyperphenylalaninemia caused by tetrahydrobiopterin synthesis deficiency

The enzyme 6-Pyruvoyl-tetrahydropterin synthase (PTS) deficiency is the major cause of BH(4)-deficient HPA. The frequency of BH(4)-deficient HPA was estimated to be around 30% among Chinese HPA population in Taiwan, which is much higher than that in Caucasian population (1.5-2% of HPA). Approximately 86% of Chinese BH(4)-deficient HPA was found to be caused by PTS-deficiency. Seven mutations - namely R25G, N52S, V56M, V70D, P87S, D96N, and T106M - had been identified in Chinese PTS-deficient patients previously. In this study, five additional mutations in the PTS gene, namely 200C>T (T67M), 226C>T (L76F), IVS3+1G>A (K54X), 116-119delTGTT (K38X) and 169-171delGTG (V57del), were identified by PCR and DNA sequencing in Chinese PTS-deficient patients. The 116-119delTGTT introduces a frameshift stop after lysine of codon 38 (K38X). The G-to-A transition at the consensus sequence of splicing donor site of exon 3 (IVS3+1G>A) resulted in exon 3 skipping of the PTS transcript and caused a frameshift stop after lysine of codon 54 (K54X). The T67M and V57del mutations have been found in Caucasian PTS deficient patients, while the L76F, IVS3+1G>A, and K38X mutations are novel. None of 100 normal alleles screened was found to have the L76F substitution, which indicated that the L76F substitution is a mutation causing PTS deficiency. Hum Mutat 18:83, 2001.

Diagnosis and treatment of 6-pyruvoyl-tetrahydropterin synthase deficiency

We detected a case of 6-pyruvoyl tetrahydropterin synthase (PTPS) deficiency during a neonatal mass screening and considered the differentiation and treatment of the peripheral form of PTPS deficiency. Although single treatment of BH4 had been started, because of the lowered biopterin (B) value, elevated neopterin (N) value, and N/B ratio in the cerebrospinal fluid (CSF), the peripheral form was judged negative and combined treatment with L-dopa and 5-hydroxy tryptophan (5-HTP) was started. Follow-up study will be necessary to confirm the diagnosis of PTPS deficiency.

[Screening for 6-pyruvoyl-tetrahydrobiopterin synthase (PTPS) deficiency: clinical analysis of 9 patients with PTPS deficiency]

OBJECTIVE

To show the incidence of 6-Pyruvoyl-tetrahydrobiopterin synthase (PTPS) deficiency among hyperphenylalaninemia and conclude the clinical outcome of patients with PTPS deficiency.

METHODS

The urinary neopterin (N) and biopterin (B) were determined by HPLC in 69 PKU cases. BH(4) loading test and mutation analysis of PTPS were performed in patients who had abnormal urinary pterin patterns. Three patients with PTPS deficiency were placed on treatment with combined synthetic BH(4) and neurotransmitter precursors such as Dopa and 5-hydroxytryptophan.

RESULTS

9 out of 69 patients, whose urinary N/B exceed 38 [normal: 1.17 (1.4)] and B% were less than 5% [normal: 55.9 (18.6)], were diagnosed as having PTPS deficiency. Four kinds of PTPS gene mutations (P87S, N52S, D96N and G144R) were detected from 4 out of 9 cases with PTPS deficiency. The last mutation was a new mutation. The three typical PTPS-deficient patients had satisfactory physical development, their intelligence quotient (IQ) were 70 approximately 80 after treatment and one partial PTPSD had normal growth and mental development.

CONCLUSION

The screening for BH(4) deficiency should be carried out among all patients with hyperphenylalaninemia in order to avoid misdiagnosis.

Dominant negative allele (N47D) in a compound heterozygote for a variant of 6-pyruvoyltetrahydropterin synthase deficiency causing transient hyperphenylalaninemia

Mutations in the 6-pyruvoyltetrahydropterin synthase (PTPS) gene result in persistent hyperphenylalaninemia and severe catecholamine and serotonin deficiencies. We investigated at the DNA level a family with a PTPS-deficient child presenting with an unusual form of transient hyperphenylalaninemia. The patient exhibited compound heterozygosity for the PTPS-mutant alleles N47D and D116G. Transfection studies with single PTPS alleles in COS-1 cells showed that the N47D allele was inactive, while D116G had around 66% of the wild-type activity. Upon co-transfection of two PTPS alleles into COS-1 cells, the N47D allele had a dominant negative effect on both the wild-type PTPS and the D116G mutant with relative reduction to about 20% of control values. Whereas the mother and the father had reduced enzyme activity in red blood cells (34.7% and 51.7%, respectively) and skin fibroblasts (2.8% and 15.4%, respectively), the clinically normal patient had in these cells activities at the detection limits, although PTPS-cross-reactive material was present in the fibroblasts. The specifically low PTPS activity in the mother's cells corroborated the evidence of a dominant negative effect of the maternal N47D allele on wild-type PTPS.

Serine 19 of human 6-pyruvoyltetrahydropterin synthase is phosphorylated by cGMP protein kinase II

6-Pyruvoyltetrahydropterin synthase (PTPS) participates in tetrahydrobiopterin cofactor biosynthesis. We previously identified in a PTPS-deficient patient an inactive PTPS allele with an Arg(16) to Cys codon mutation. Arg(16) is located in the protein surface exposed phosphorylation motif Arg(16)-Arg-Ile-Ser, with Ser(19) as the putative phosphorylation site for serine-threonine protein kinases. Purification of recombinant PTPS-S19A from bacterial cells resulted in an active enzyme (k(cat)/K(m) = 6.4 x 10(3) M(-1) s(-1)), which was similar to wild-type PTPS (k(cat)/K(m) = 4.1 x 10(3) M(-1) s(-1)). In assays with purified enzymes, wild-type but not PTPS-S19A was a specific substrate for the cGMP-dependent protein kinase (cGK) type I and II. Upon expression in COS-1 cells, PTPS-S19A was stable but not phosphorylated and had a reduced activity of approximately 33% in comparison to wild-type PTPS. Extracts from several human cell lines, including brain, contained a kinase that bound to and phosphorylated immobilized wild-type, but not mutant PTPS. Addition of cGMP stimulated phosphotransferase activity 2-fold. Extracts from transfected COS-1 cells overexpressing cGKII stimulated Ser(19) phosphorylation more than 100-fold, but only 4-fold from cGKI overexpressing cells. Moreover, fibroblast extracts from mice lacking cGKII exhibited significantly reduced phosphorylation of PTPS. These results suggest that Ser(19) of human PTPS may be a substrate for cGKII phosphorylation also in vivo, a modification that is essential for normal activity.

Molecular characterization of 6-pyruvoyl-tetrahydropterin synthase deficiency in Japanese patients

We identified three mutations in four Japanese patients with central type 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. One missense mutation was a C-to-T transition, resulting in the substitution of Pro by Ser at codon 87 (P87S) in exon 5. Another missense mutation was a G-to-A transition, resulting in the substitution of Asp by Asn at codon 96 (D96N) in exon 5. A splicing mutation was found by skipping of exon 4 on PTPS mRNA analysis, and a G-to-A transition at the third base of codon 81 (E81E) and at the terminal base in exon 4 were detected on genomic PTPS DNA analysis. The E81E mutation affected the splice donor site of exon 4 and caused the splicing error. In COS cell expression analysis, the P87S and D96N mutant constructs revealed, respectively, 52% and 10% of wild-type activity. Patients with P87S/P87S (52%/52% in-vitro PTPS activity) exhibited 0.11 and 0 microU/g hemoglobin [Hb] in erythrocyte PTPS activity (wild-type control: 11-29 microU/gHb) erythrocyte PTPS activity, and the patient with P87S/D96N mutations (52%/10%) had 0.97 microU/gHb in PTPS erythrocyte activity. The PTPS erythrocyte activity did not coincide with the in-vitro PTPS activity based on patient genotype.

Retrovirus-mediated double transduction of the GTPCH and PTPS genes allows 6-pyruvoyltetrahydropterin synthase-deficient human fibroblasts to synthesize and release tetrahydrobiopterin

The tetrahydrobiopterin (BH4) cofactor is essential for the aromatic amino acid hydroxylases that are involved in phenylalanine degradation and catecholamine and serotonin biosynthesis. Furthermore, BH4 is an essential and limiting cofactor for all types of nitric oxide synthases. BH4 deficiency results in hyperphenylalaninemia and monoamine neurotransmitter depletion associated with progressive mental retardation and is most commonly due to autosomal recessive mutations in 6-pyruvoyltetrahydropterin synthase (PTPS), the second enzyme for cofactor biosynthesis. Due to the relatively poor blood-brain barrier penetration of the cofactor, conventional therapy requires, besides oral doses of synthetic BH4, administration of neurotransmitter precursors and an aromatic amino acid decarboxylase inhibitor. The outcome of this therapy is not always beneficial. In this study we transduced into primary patient fibroblasts the human cDNAs for the BH4 biosynthetic enzymes GTP cyclohydrolase I and PTPS, expressed from different retroviral vectors. This allowed BH4 biosynthesis in originally PTPS-deficient cells. Moreover, the double-transduced fibroblasts released between 200 and 800 pmol of BH4/10(6) cells/day. Such engineered fibroblasts may be grafted into the central nervous system and used as depository cells for constitutive delivery of BH4.

Hyperprolactinemia, a tool in treatment control of tetrahydrobiopterin deficiency: endocrine studies in an affected girl

Severe tetrahydrobiopterin (BH4) deficiency is a naturally occurring model of cerebral catecholamine and serotonin shortage. Examination of the stimulated release and physiologic secretion pattern of several hormones in affected individuals permits certain conclusions concerning the involvement of these neurotransmitters in hormone regulation. Treatment, moreover, permits the ranking of the quality of the therapeutic regimens in use according to the degree of hormonal alteration. The 24-h secretion pattern of prolactin, GH, cortisol, and melatonin and the stimulated release of prolactin, GH, TSH, and gonadotropins were studied in an affected girl. Severe hyperprolactinemia with disruption of the pulsatile and circadian secretion pattern was the prevailing feature. The GH physiologic secretion pattern was not affected, but its stimulation was impaired. Melatonin displayed a normal circadian secretion pattern; the rhythm, however, was advanced by several hours. Conventional treatment of BH4 deficiency, i.e. BH4, 5-hydroxytryptophan, and L-DOPA/carbidopa (the last named given in three doses per day), suppresses prolactin levels merely for a few hours. L-DOPA/carbidopa given at shorter intervals or, even better, as a slow release preparation, is more effective in suppressing prolactin levels. Our data indicate immense hyperprolactinemia but few other hormonal disturbances in severe BH4 deficiency. Prolactin secretion may serve as an extremely sensitive marker for the hypothalamic dopamine content under different therapeutic regimens. Treatment with an L-DOPA/carbidopa slow release preparation produces virtually normal prolactin levels.