Frequency of GCH1 deletions in Dopa-responsive dystonia

The treatment and clinical follow-up outcome in Iranian patients with tetrahydrobiopterin deficiency

OBJECTIVES

This study aimed to evaluate the biochemical factors, genetic mutations, outcome of treatment, and clinical follow-up data of Iranian patients with tetrahydrobiopterin (BH4) deficiency from April/2016 to March/2020.

METHODS

Forty-seven BH4 deficiency patients were included in the study and underwent biochemical and genetic analyses. The clinical outcomes of the patients were evaluated after long-term treatment.

RESULTS

Out of the 47 (25 females and 22 males) BH4 deficiency patients enrolled in the study, 23 were Dihydropteridine reductase (DHPR) deficient patients, 23 were 6-pyruvoyl-tetrahydropterin synthase (PTPS) deficient patients, and one was GTP-Cyclohydrolase 1 deficiency (GTPCH-1) patient. No clinical symptoms were observed in 10 of the DHPR deficient patients (before and after the treatment). Also, most patients diagnosed at an early age had a proper response to the treatment. However, drug therapy did not improve clinical symptoms in three of the patients diagnosed at the age of over 10 years. Also, 16 PTPS deficiency patients who were detected within 6 months and received treatment no clinical symptoms were presented. One of the patients was detected with GTPCH deficiency. Despite being treated with BH4, this patient suffered from a seizure, movement disorder, mental retardation, speech difficulty, and hypotonia.

CONCLUSIONS

The study results showed that neonatal screening should be carried out in all patients with hyperphenylalaninemia because early diagnosis and treatment can reduce symptoms and prevent neurological impairments. Although the BH4 deficiency outcomes are highly variable, early diagnosis and treatment in the first months of life are crucial for good outcomes.

A case report of DOPA-responsive dystonia in a young woman

Dopa-responsive dystonia (DRD) is a rare progressive genetically heterogenous disorder with pediatric onset. DRD is 3 times as prevalent in women than in men. This article reports a clinical case of DRD in a young female presenting with paraparesis, foot dystonia (more pronounced in the right foot) and pronounced walking impairment, who was admitted for emergency treatment to a Neurology Unit. Based on the additional tests, which included a levodopa trial and Sanger sequencing, the patient was diagnosed with DRD. Levodopa caused a considerable improvement of the symptoms. The article describes the clinical features of the disease, talks about its differential diagnosis, genetic predisposition and treatment strategy.

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.

Clinical and Genetic Heterogeneity in a Cohort of Chinese Children With Dopa-Responsive Dystonia

Background: The aim of this study was to investigate the genetic and clinical features of dopa-responsive dystonia (DRD) in China. Method: Characteristics of gene mutations and clinical manifestations of 31 patients diagnosed with DRD were analyzed retrospectively. Result: From January 2000 to January 2019, 31 patients were diagnosed with DRD. Twenty (64.5%) were male, and 11 (35.5%) were female. Ten patients (32.3%) had classic DRD, 19 (61.3%) had DRD-plus, and 2 (6.4%) patients had mutations in the dopamine synthetic pathway (PTS gene mutation) without a typical phenotype (not DRD or DRD-plus). Twenty-eight (90.3%) patients underwent genetic testing. Homozygous or compound heterozygous TH gene mutations were found in 22 patients. GCH1 and PTS gene mutations were found in 2 patients. Heterozygous TH mutation and genetic testing were negative in 1 patient. They took different doses of L-dopa, ranging from 0.4 to 8.7 mg/kg/d. Patients with classic DRD responded well. In patients with DRD-plus, 94.7% (18/19) responded well with residual symptoms. One patient (5.3%) did not show any improvement. Conclusion: DRD can be divided into classic DRD and DRD-plus. In this cohort, the most common pathogenic gene was TH. Fever was the important inducing factor of the disease. L-dopa has sustained and stable effects on patients with classic DRD. In patients with DRD-plus, treatment with L-dopa could ameliorate most of the symptoms.

Atypical presentation of dopa-responsive dystonia in Taiwan

The typical clinical presentation of dopa-responsive dystonia, which is also called Segawa disease, is a young age of onset, with predominance in females, diurnal fluctuation of lower limb dystonia, and fair response to low-dose levodopa. This disease has both autosomal dominant and autosomal recessive inheritance. Autosomal dominant Segawa disease is caused by GCH1 mutation on chromosome 14q22.1-q22.2. Here, we report the case of a male patient with genetically confirmed Segawa disease and atypical presentations including no diurnal symptom fluctuation and insufficient response to levodopa. The patient's father who had the same mutation presented parkinsonism in old age. We also review the literature to address the broad clinical heterogeneity of Segawa disease and the influence of onset age on clinical presentation.

Variability of presynaptic nigrostriatal dopaminergic function and clinical heterogeneity in a dopa-responsive dystonia family with GCH-1 gene mutation

We studied the presynaptic nigrostriatal dopaminergic function using single photon emission computed tomography (SPECT) imaging of a ^99mTc-TRODAT-1 (TRODAT) scan in a dopa-responsive dystonia (DRD) family with the guanosine triphosphate cyclohydrolase 1 (GCH-1) gene mutation. Clinically, there was presentation of intrafamilial variability in the DRD family. The index patient was a 10-year-old girl with classic DRD and normal presynaptic nigrostriatal dopaminergic function. However, her grandmother, a 79-year-old woman, presented with slowly progressive Parkinson's disease (PD) without dystonic symptoms and excellent response to dopaminergic therapy for 21 years. Her brain TRODAT SPECT imaging revealed a markedly and asymmetrically reduced uptake of dopamine transporter at the bilateral striatum. Her father, a 54-year-old man, was an asymptomatic gene carrier and his brain TRODAT SPECT imaging revealed asymmetrically reduced nigrostriatal dopaminergic transmission in the bilateral striatum. We conclude variability of presynaptic nigrostriatal dopaminergic function in patients with DRD is related to their clinical heterogeneity. Significantly, impairment of presynaptic dopamine function actually occurs in the asymptomatic gene carrier.

Complex and Dynamic Chromosomal Rearrangements in a Family With Seemingly Non-Mendelian Inheritance of Dopa-Responsive Dystonia

Importance

Chromosomal rearrangements are increasingly recognized to underlie neurologic disorders and are often accompanied by additional clinical signs beyond the gene-specific phenotypic spectrum.

Objective

To elucidate the causal genetic variant in a large US family with co-occurrence of dopa-responsive dystonia as well as skeletal and eye abnormalities (ie, ptosis, myopia, and retina detachment).

Design, Setting, and Participants

We examined 10 members of a family, including 5 patients with dopa-responsive dystonia and skeletal and/or eye abnormalities, from a US tertiary referral center for neurological diseases using multiple conventional molecular methods, including fluorescence in situ hybridization and array comparative genomic hybridization as well as large-insert whole-genome sequencing to survey multiple classes of genomic variations. Of note, there was a seemingly implausible transmission pattern in this family due to a mutation-negative obligate mutation carrier.

Main Outcomes and Measures

Genetic diagnosis in affected family members and insight into the formation of large deletions.

Results

Four members were diagnosed with definite and 1 with probable dopa-responsive dystonia. All 5 affected individuals carried a large heterozygous deletion encompassing all 6 exons of GCH1. Additionally, all mutation carriers had congenital ptosis requiring surgery, 4 had myopia, 2 had retinal detachment, and 2 showed skeletal abnormalities of the hands, ie, polydactyly or syndactyly or missing a hand digit. Two individuals were reported to be free of any disease. Analyses revealed complex chromosomal rearrangements on chromosome 14q21-22 in unaffected individuals that triggered the expansion to a larger deletion segregating with affection status. The expansion occurred recurrently, explaining the seemingly non-mendelian inheritance pattern. These rearrangements included a deletion of GCH1, which likely contributes to the dopa-responsive dystonia, as well as a deletion of BMP4 as a potential cause of digital and eye abnormalities.

Conclusions and Relevance

Our findings alert neurologists to the importance of clinical red flags, ie, unexpected co-occurrence of clinical features that may point to the presence of chromosomal rearrangements as the primary disease cause. The clinical management and diagnostics of such patients requires an interdisciplinary approach in modern clinical-diagnostic care.

Novel GCH1 variant in Dopa-responsive dystonia and Parkinson's disease

Background

GTP cyclohydrolase I (GCH1) mutations are the commonest cause of Dopa-responsive dystonia (DRD). Clinical phenotypes can be broad, even within a single family.

Methods

We present clinical, genetic and functional imaging data on a British kindred in which affected subjects display phenotypes ranging from DRD to Parkinson's disease (PD). Twelve family members were studied. Clinical examination, dopamine transporter (DAT) imaging, and molecular genetic analysis of GCH1 and the commonest known familial PD-related genes were performed.

Results

We have identified a novel missense variant, c.5A > G, p.(Glu2Gly), within the GCH1 gene in affected family members displaying a range of phenotypes.

Two affected subjects carrying this variant had abnormal DAT imaging. These two with abnormal DAT imaging had a PD phenotype, while the remaining three subjects with the novel GCH1 variant had normal DAT imaging and a DRD phenotype.

Conclusions

We propose that this GCH1 variant is pathogenic in this family and these findings suggest that similar mechanisms involving abnormal GTP cyclohydolase I may underlie both PD and DRD. GCH1 genetic testing should be considered in patients with PD and a family history of DRD.

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We have identified a novel missense variant, c.5A > G, p.(Glu2Gly), within the GCH1 gene in family with Dopa responsive dystonia (DRD) and parkinsonism.

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Those with parkinsonism had abnormal DaTscans, indicating nigrostriatal neurodegeneration.

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These findings suggest that similar mechanisms involving abnormal GTP cyclohydolase I may underlie both Parkinson's disease and Dopa responsive dystonia.

Clinical spectrum of dopa-responsive dystonia and related disorders

Dopa-responsive dystonia (DRD) has a classic presentation of childhood or adolescent-onset dystonia, mild parkinsonism, marked diurnal fluctuations, improvement with sleep or rest, and a dramatic and sustained response to low doses of L-dopa without motor fluctuations or dyskinesias. However, there have been many papers on patients with a wide range of features, which report them as DRD mainly because they had dystonic syndromes with L-dopa responsiveness. Many mutations in the dopaminergic system have been found as molecular genetic defects. Therefore, the clinical and genetic spectra of DRD are unclear, which lead to difficulties in diagnostic work-ups and planning treatments. We propose the concept of DRD and DRD-plus to clarify the confusion in this area and to help understand the pathophysiology and clinical features, which will help in guiding diagnostic investigations and planning treatments. We critically reviewed the literature on atypical cases and discussed the limitations of the gene study.

GTP cyclohydrolase I and tyrosine hydroxylase gene mutations in familial and sporadic dopa-responsive dystonia patients

Dopa-responsive dystonia (DRD) is a rare inherited dystonia that responds very well to levodopa treatment. Genetic mutations of GTP cyclohydrolase I (GCH1) or tyrosine hydroxylase (TH) are disease-causing mutations in DRD. To evaluate the genotype-phenotype correlations and diagnostic values of GCH1 and TH mutation screening in DRD patients, we carried out a combined study of familial and sporadic cases in Chinese Han subjects. We collected 23 subjects, 8 patients with DRD, 5 unaffected family members, and 10 sporadic cases. We used PCR to sequence all exons and splicing sites of the GCH1 and TH genes. Three novel heterozygous GCH1 mutations (Tyr75Cys, Ala98Val, and Ile135Thr) were identified in three DRD pedigrees. We failed to identify any GCH1 or TH mutation in two affected sisters. Three symptom-free male GCH1 mutation carriers were found in two DRD pedigrees. For those DRD siblings that shared the same GCH1 mutation, symptoms and age of onset varied. In 10 sporadic cases, only two heterozygous TH mutations (Ser19Cys and Gly397Arg) were found in two subjects with unknown pathogenicity. No GCH1 and TH mutation was found in 40 unrelated normal Han Chinese controls. GCH1 mutation is the main etiology of familial DRD. Three novel GCH1 mutations were identified in this study. Genetic heterogeneity and incomplete penetrance were quite common in DRD patients, especially in sporadic cases. Genetic screening may help establish the diagnosis of DRD; however, a negative GCH1 and TH mutation test would not exclude the diagnosis.

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.

Two novel mutations of the GTP cyclohydrolase 1 gene and genotype-phenotype correlation in Chinese Dopa-responsive dystonia patients

The most common form of Dopa-responsive dystonia (DRD) is caused by heterozygous mutations in the GTP cyclohydrolase I (GCH1) gene. We screened two unrelated, DRD-symptomatic Chinese Han individuals, for GCH1 gene mutations by direct sequencing. As the clinical manifestations of DRD are highly variable, we also explored the association between genotype and phenotype in all Chinese DRD patients reported so far in the literature, comprising 62 DRD-affected patients from 36 Chinese families. Two novel missense mutations (T94M, L145F) and a novel variant (c. 453+6 G>T) were identified in our two new patients. None of these variants was detected in 200 healthy controls. On the basis of this and other reports, heterozygous mutations were detected in 90.3% of Chinese Han subjects with DRD. Seeming the age of onset for males and females, the mean age was 13 years older in males than in females (P=0.006). Different mutation types did not show any significant differences in age of onset, gender composition, initial symptoms, or the L-dopa dose that abolished the symptoms. Among DRD patients lacking missense or exon-intron boundary mutations, 68.4% were found to possess a large deletion in GCH1, which were detected by multiplex ligation-dependent probe amplification. Most GCH1 mutations were found to cluster in two regions of the coding sequence, suggesting the probable existence of mutation hotspot for the first time. The genotype-phenotype correlation described here may improve our understanding of DRD in Chinese individuals.

Guanosine triphosphate cyclohydrolase 1 promoter deletion causes dopa-responsive dystonia

BACKGROUND

Autosomal dominant dopa-responsive dystonia (AD-DRD) is caused by a biochemical defect primarily resulting from guanosine triphosphate cyclohydrolase 1 gene (GCH1) mutations. Few families have been reported without mutations in GCH1.

METHODS

Genome-wide linkage analysis and positional cloning to identify the genetic defect in a Belgian AD-DRD family was carried out.

RESULTS AND CONCLUSION

In this study, we report on the identification and characterization of a novel 24-kb deletion spanning exon 1 and the 5' regulatory region of GCH1 causing a wide spectrum of motor and nonmotor symptoms in a large Belgian AD-DRD family. This large-scale deletion of regulatory sequences leads to decreased GCH1 activity in all carriers, most probably resulting from allelic loss of transcription. We mapped the breakpoints of this deletion to the nucleotide level, allowing the development of a straightforward polymerase chain reaction assay for fast, efficient detection of this large deletion, which will prove valuable for preimplantation genetic diagnosis.

Urinary neopterin and phenylalanine loading test as tools for the biochemical diagnosis of segawa disease

Background. The diagnosis of autosomal dominant GTP-cyclohydrolase deficiency relies on the examination of the GCH1 gene and/or pterins and neurotransmitters in CSF. The aim of the study was to assess the diagnostic value, if any, of pterins in urine and blood phenylalanine (Phe) and tyrosine (Tyr) under oral Phe loading test. Methods. We report on two new pedigrees with four symptomatic and four asymptomatic carriers whose pattern of urinary pterins and blood Phe/Tyr ratio under oral Phe loading pointed to GTP-cyclohydrolase deficiency. The study was then extended to 3 further patients and 90 controls. The diagnostic specificity and sensitivity of these metabolic markers were analysed by backwards logistic analysis. Results. Two genetic alterations segregated alternatively in Family 1 (c.631-632 del AT and c.671A > G), while exon 1 deletion was transmitted along three generations in Family 2. Neopterin and biopterin concentrations in urine clustered differently in controls under and over the age of 15. Therefore patients and controls were sub grouped according to this age. Neopterin was significantly reduced in GCH1 mutated subjects younger than 15, and both neopterin and biopterin in those older than 15. Moreover, the Phe/Tyr ratios at the second and third hour were both significantly higher in patients than in controls. Backwards logistic regression demonstrated the high diagnostic sensitivity and specificity of combined values of neopterin concentration and Phe/Tyr ratio at the second hour. Conclusions. Pterins in urine and Phe loading test are non-invasive and reliable tools for the biochemical diagnosis of GTP-cyclohydrolase deficiency.

Guanine triphosphate-cyclohydrolase 1-deficient dopa-responsive dystonia presenting as frequent falling in 2 children

Guanine triphosphate (GTP)-cyclohydrolase 1 (GCH1)-deficient dopa-responsive dystonia is caused by GCH1 gene mutation. Two children presenting with frequent daily falling are reported with GCH1 gene mutations with persistent response to low-dose levodopa/carbidopa. Typical and atypical clinical features associated with GCH1 mutations are also reviewed.

Milestones in dystonia

The last 25 years have seen remarkable advances in our understanding of the genetic etiologies of dystonia, new approaches into dissecting underlying pathophysiology, and independent progress in identifying effective treatments. In this review we highlight some of these advances, especially the genetic findings that have taken us from phenomenological to molecular-based diagnoses. Twenty DYT loci have been designated and 10 genes identified, all based on linkage analyses in families. Hand in hand with these genetic findings, neurophysiological and imaging techniques have been employed that have helped illuminate the similarities and differences among the various etiological dystonia subtypes. This knowledge is just beginning to yield new approaches to treatment including those based on DYT1 animal models. Despite the lag in identifying genetically based therapies, effective treatments, including impressive benefits from deep brain stimulation and botulinum toxin chemodenervation, have marked the last 25 years. The challenge ahead includes continued advancement into understanding dystonia's many underlying causes and associated pathology and using this knowledge to advance treatment including preventing genetic disease expression.

EFNS guidelines on diagnosis and treatment of primary dystonias

OBJECTIVES

to provide a revised version of earlier guidelines published in 2006.

BACKGROUND

primary dystonias are chronic and often disabling conditions with a widespread spectrum mainly in young people.

DIAGNOSIS

primary dystonias are classified as pure dystonia, dystonia plus or paroxysmal dystonia syndromes. Assessment should be performed using a validated rating scale for dystonia. Genetic testing may be performed after establishing the clinical diagnosis. DYT1 testing is recommended for patients with primary dystonia with limb onset before age 30, and in those with an affected relative with early-onset dystonia. DYT6 testing is recommended in early-onset or familial cases with cranio-cervical dystonia or after exclusion of DYT1. Individuals with early-onset myoclonus should be tested for mutations in the DYT11 gene. If direct sequencing of the DYT11 gene is negative, additional gene dosage is required to improve the proportion of mutations detected. A levodopa trial is warranted in every patient with early-onset primary dystonia without an alternative diagnosis. In patients with idiopathic dystonia, neurophysiological tests can help with describing the pathophysiological mechanisms underlying the disorder.

TREATMENT

botulinum toxin (BoNT) type A is the first-line treatment for primary cranial (excluding oromandibular) or cervical dystonia; it is also effective on writing dystonia. BoNT/B is not inferior to BoNT/A in cervical dystonia. Pallidal deep brain stimulation (DBS) is considered a good option, particularly for primary generalized or cervical dystonia, after medication or BoNT have failed. DBS is less effective in secondary dystonia. This treatment requires a specialized expertise and a multidisciplinary team.

An intragenic duplication in guanosine triphosphate cyclohydrolase-1 gene in a dopa-responsive dystonia family

BACKGROUND

Autosomal dominant dopa-responsive dystonia is commonly caused by mutations in the guanosine triphosphate cyclohydrolase-1 gene.

METHODS

We report a British family that has been followed for more than 20 years in which no mutations were previously identified.

RESULTS

Reanalysis of this pedigree detected a duplication of guanosine triphosphate cyclohydrolase-1 exon 2 in affected family members. mRNA analysis showed a mutant transcript with a tandem exon 2 duplication. Four family members developed dopa-responsive dystonia, with onset in their late teens, and subsequently developed restless leg syndrome and migraine.

CONCLUSIONS

This is the first report of an intragenic guanosine triphosphate cyclohydrolase-1 duplication in a dopa-responsive dystonia family.

GCH1 mutation and clinical study of Chinese patients with dopa-responsive dystonia

Dopa-responsive dystonia (DRD) is typically caused by heterozygous mutations in GTP cyclohydrolase 1 gene (GCH1). Our aim was to investigate the clinical and genetic features of Chinese DRD patients. We analyzed a cohort of Chinese DRD patients' clinical data. Mutation of the GCH1 gene was screened by direct sequencing. Additionally, multiplex ligation-dependent probe amplification (MLPA) assay targeting the GCH1 and the TH gene to evaluate large exon deletion or duplicate mutation of the genes were performed in point mutation-negative patients. Ten sporadic DRD patients and two pedigrees including six patients were included in the study. The onset age ranged from 3 to 15 years old. All patients initially presented with walking problems due to lower limb dystonia. The delay between onset and diagnosis ranged from 1 to 42 years old. The symptoms were completely or near-completely abolished with low dose levodopa treatment (dosages ranged from 25 mg to 400 mg/day). Direct sequencing in 14 patients found two known mutations (Gly203Arg in exon 5 in four unrelated patients and Met102Lys in exon 1 in one patient) and one new mutation (Thr186Ile mutation in exon 5 in two unrelated pedigrees). A heterozygous exon 2 deletion in the GCH1 gene was found in one of three point mutation-negative patients by MLPA analysis. Our clinical findings in DRD patients were consistent with other studies. GCH1 gene mutations were quite common in Chinese patients. MPLA should be performed in routine deletion analysis of GCH1 in point mutation-negative DRD patients.

High frequency of multiexonic deletion of the GCH1 gene in a Taiwanese cohort of dopa-response dystonia

Large deletions in the GCH1 gene have been reported in a minority of cases of dopa-responsive dystonia (DRD). In this study, we performed an extensive clinical and genetic investigation of 22 affected members in eight families. Sequence analysis revealed five different mutations in five families (n = 10); Ser81Pro (novel), Ser76X, Gly203Arg, 249del A, and IVS5 + 3insT. Applying multiple ligation-dependent probe amplification analysis, we detected a large heterozygous deletion of exons 1-3 in the remaining three families (n = 12), which was verified by quantitative real-time PCR analysis. Therefore, the large deletion accounted for 37.5% of the total families and 55% of our DRD population. The deletion appeared to have high penetrance and was associated with multifocal dystonia and adult onset in males. Adult-onset patients were commonly presenting with resting tremor, rigidity, and bradykinesia, indistinguishable from those in Parkinson's disease. In conclusion, a high frequency of multiexonic deletion of GCH1 was identified in the Taiwanese DRD population. By dosage analysis, we were able to detect a mutation in all patients. Our study demonstrates that dosage analysis is necessary for molecular diagnostics in DRD patients of Han Chinese ethnicity.

Exhaustive analysis of BH4 and dopamine biosynthesis genes in patients with Dopa-responsive dystonia

Dopa-responsive dystonia is a childhood-onset dystonic disorder, characterized by a dramatic response to low dose of L-Dopa. Dopa-responsive dystonia is mostly caused by autosomal dominant mutations in the GCH1 gene (GTP cyclohydrolase1) and more rarely by autosomal recessive mutations in the TH (tyrosine hydroxylase) or SPR (sepiapterin reductase) genes. In addition, mutations in the PARK2 gene (parkin) which causes autosomal recessive juvenile parkinsonism may present as Dopa-responsive dystonia. In order to evaluate the relative frequency of the mutations in these genes, but also in the genes involved in the biosynthesis and recycling of BH4, and to evaluate the associated clinical spectrum, we have studied a large series of index patients (n = 64) with Dopa-responsive dystonia, in whom dystonia improved by at least 50% after L-Dopa treatment. Fifty seven of these patients were classified as pure Dopa-responsive dystonia and seven as Dopa-responsive dystonia-plus syndromes. All patients were screened for point mutations and large rearrangements in the GCH1 gene, followed by sequencing of the TH and SPR genes, then PTS (pyruvoyl tetrahydropterin synthase), PCBD (pterin-4a-carbinolamine dehydratase), QDPR (dihydropteridin reductase) and PARK2 (parkin) genes. We identified 34 different heterozygous point mutations in 40 patients, and six different large deletions in seven patients in the GCH1 gene. Except for one patient with mental retardation and a large deletion of 2.3 Mb encompassing 10 genes, all patients had stereotyped clinical features, characterized by pure Dopa-responsive dystonia with onset in the lower limbs and an excellent response to low doses of L-Dopa. Dystonia started in the first decade of life in 40 patients (85%) and before the age of 1 year in one patient (2.2%). Three of the 17 negative GCH1 patients had mutations in the TH gene, two in the SPR gene and one in the PARK2 gene. No mutations in the three genes involved in the biosynthesis and recycling of BH4 were identified. The clinical presentations of patients with mutations in TH and SPR genes were strikingly more complex, characterized by mental retardation, oculogyric crises and parkinsonism and they were all classified as Dopa-responsive dystonia-plus syndromes. Patient with mutation in the PARK2 gene had Dopa-responsive dystonia with a good improvement with L-Dopa, similar to Dopa-responsive dystonia secondary to GCH1 mutations. Although the yield of mutations exceeds 80% in pure Dopa-responsive dystonia and Dopa-responsive dystonia-plus syndromes groups, the genes involved are clearly different: GCH1 in the former and TH and SPR in the later.

Novel non-sense GCH1 mutation in a South African family diagnosed with dopa-responsive dystonia

BACKGROUND

Dopa-responsive dystonia (DRD), a movement disorder characterized by onset in early childhood and a dramatic response to low doses of levodopa, has been shown to be caused by a number of different mutations in the GCH1 gene.

METHODS

We identified a South African family which presented with DRD in three family members. Polymerase chain reaction (PCR) primers were designed to span all six exons of GCH1 and the PCR products were screened for pathogenic mutations using direct sequencing.

RESULTS

A novel non-sense mutation (c.233delT; p.I78fsX79) was identified in the DRD patients, which would produce a markedly truncated protein of only 78 amino acids. This mutation was also present in a number of asymptomatic family members.

CONCLUSIONS

A novel non-sense mutation in the GCH1 gene can be associated with DRD and reduced penetrance in South African patients.