The GTP cyclohydrolase I gene in Russian families with dopa-responsive dystonia

A Case of GCH-1 Mutation Dopa-Responsive Dystonia Requiring High Doses of Levodopa for Treatment

Background:

Mutations in the GCH-1 gene are associated with Autosomal Dominant Dopamine Responsive Dystonia (DYT 5). One of the hallmarks of this condition is dramatic and sustained response to low doses of levodopa.

Case Report:

We present the case of a 22 year old female patient with genetically confirmed GCH-1 Dopa-Responsive Dystonia who had no response to low dose Levodopa but who achieved symptom control on a total dose of 900 mg/day.

Discussion:

Autosomal Dominant Dopa-Responsive Dystonia is a phenotypical heterogenous condition that, in some cases, may require high doses of levodopa for treatment response.

Highlights

Mutations in the GCH-1 gene are associated with Autosomal Dominant Dopamine Responsive Dystonia which is typically defined by dramatic responses to low doses of levodopa. We report a patient with genetically confirmed Dopa-Responsive Dystonia who had no response to low dose Levodopa but who achieved symptom control with 900 mg/day.

[Dopa-responsive dystonia]

BACKGROUND/AIM

Dystonia is considered to be a prolonged involuntary contractions of the muscles leading to twisting, repetitive movements or irregular postures. Etiologically, it could be classified as primary and secondary dystonia. Dopa-responsive dystonia (DRD) belongs to a group of primary dystonia. The aim of this study was to detect the presence of gene GCH-I mutation in our population in patients with dopa-responsive dystonic dyskinesia and to analyse clinical specificity of the affected.

METHODS

Out of the group of patients with dystonia of different distribution four patients were separated whose clinical picture indicated the diagnosis of DRD. Two patients had a positive family anamnesis while the other two were sporadic. Genetic analysis was performed by the use of a standard protocol, which included PCR amplification and DNK sequencing according to the method of Senger and autoradiografy.

RESULTS

In the patients from the family DRD-1 new hetaerazygote point mutation 520G-->A in 4-m exson gene GCH-I was revealed. First symptoms of the disease showed in the age of seven by the torsion of the left foot, progressively advanced and got into the evolution of numbness in the legs, aggravated gait, tending to worsen in the evening, and the therapy with levodopa (500 mg) produced a dramatic effect. The second mutation in the female patient from the family DRD-2 was homozygote deletion in 1-m intron gene GCH-I (IVS1-85delA). Unwilling torsion of the foot, feeling of weakness in the lower extremities (that caused falling without loss of the consciousness) were clinical demonstrations of the disease. The application of levodopa (300 mg) caused regression of the symptoms of the disease. Hetaerazygote deletion of adenine in the position 209 in the first exon (209del A) was identificated in the patient DRD-3 with negative family anamnesis, in who in the age of ten the torsion of the foot inside occured for the first time following by trembling of both the left and right legs at rest; after a few years, tremor of hands also appeared, which became worse in stressful situations. The father of the patient was an asymptomatic bearer of mutation. The fourth mutation in gene GCH-I was found in I exon gene GCH-I, 208delA. The disease was started by torsion of the left foot, progressing easily, and worsening in the evenings, but at the age of 30, moving became harder, fatigue and pain in muscles, increased and at the age of 40 the patient recognised the change of speech. The application of levodopa (300 mg/daily) made the patient feel better and walk independently.

CONCLUSION

The study presented four patients with genetic confirmation of the diagnosis of dopa-responsive dystonia. This entity is very significant in differential diagnostics of both early dystonia (< 26 years) and early parkinsonism (< 40 years) since it can be successfully managed by applyng relatively low doses of levodopa over a long period of time.

Gene mutation in hereditary progressive dystonia with marked diurnal fluctuation (HPD), strictly defined dopa-responsive dystonia

Mutations of the guanosine triphosphate (GTP)-cyclohydrolase I (GCH-I) gene, which catalyzes the first step in the tetrahydrobiopterin (the natural cofactor for tyrosine hydroxylase) biosynthesis, are demonstrated to cause HPD, i.e. strictly defined dopa-responsive dystonia. We analyzed the GCH-I gene of patients who fulfilled clinical criteria for typical hereditary progressive dystonia (HPD) to finalize the diagnosis. Two novel point mutations in two independent families and one novel de novo point mutation in one sporadic patient were identified. In a Japanese family, a T-to-C transition was found at exon 2, which resulted in a substitution of Cys 141 to Arg. In another Japanese family, a C-to-T mutation in exon 4 caused a nonsense codon Gln180Stop. In a clinically sporadic Japanese patient, T-to-G transition in exon 1 brought Met 102 Arg missense mutation, which was not observed in its biological parents. These three mutations were not observed in previously reported 57 pedigrees/patients and no polymorphisms in the coding region of the GCH-I gene were identified. None of the mutations of GCH-I gene in HPD reported to date or in this study have been detected more than once in any ethnicity suggesting a relatively high spontaneous mutation rate in this gene.

Levodopa-responsive dystonia. GTP cyclohydrolase I or parkin mutations?

Autosomal dominant DOPA-responsive dystonia (DRD) is usually caused by mutation in the gene encoding guanosine triphosphate-cyclohydrolase I (GTPCH I). We studied 22 families with a phenotype of levodopa-responsive dystonia by sequencing the six coding exons, the 5'-untranslated region and the exon-intron boundaries of the GTPCH I gene. Eleven heterozygous mutations were identified, including five missense mutations, one splice site mutation, two small deletions and two nonsense mutations, in 12 families that included 27 patients and 13 asymptomatic carriers. Six mutations were new and five had already been reported. Four of the mutations caused truncation of the GTPCH I protein. One family carried a base-pair change in the 5'-untranslated region, not detected in controls, that could be responsible for the phenotype. Three of the remaining 10 families had deletions in the parkin gene on chromosome 6, underlining how difficult it is to distinguish, in some cases, between DRD and parkin mutations. No mutations were identified in seven families. The clinical spectrum extended from the classical DRD phenotype to parkinsonism with levodopa-induced dyskinesias, and included spastic paraplegia as well as the absence of dystonia.

Molecular genetics of dopa-responsive dystonia

The causative genes of two types of hereditary dopa-responsive dystonia (DRD) due to dopamine (DA) deficiency in the nigrostriatum DA neurons have been elucidated. Autosomal dominant DRD (AD-DRD) was originally described by Segawa as hereditary progressive dystonia with marked diurnal fluctuation (HPD). We cloned the human GTP cyclohydrolase I (GCH1) gene, and mapped the gene to chromosome 14q22.1-q22.2 within the HPD/DRD locus, which had been identified by linkage analysis. GCH1 isthe rate-limiting enzyme for the biosynthesis of tetrahydrobiopterin (BH4), the cofactor for tyrosine hydroxylase (TH), which is the first and rate-limiting enzyme of DA synthesis. We proved that the GCH1 gene is the causative gene for HPD/DRD based on the identification of mutations of the gene in the patients and decreases in the enzyme activity expressed in mononuclear blood cells to 2-20% of the normal value. About 60 different mutations (missense, nonsense, and frameshift mutations) in the coding region or in the exon-intron junctions of the GCH1 gene have been reported in patients with AD-DRD all over the world. Recent findings indicate that the decreased GCH1 activity in AD-DRD may be caused by the negative interaction of the mutated subunit with the wild-type one, i.e., a dominant negative effect, and/or by decreases in the levels of GCH1 mRNA and protein caused by inactivation of one allele of the GCH1 gene. Autosomal recessive DRD (AR-DRD) with Segawa's syndrome was discovered in Germany. The AR-DRD locus was mapped to chromosome 11p15.5 in the chromosomal site of the TH gene. In the AR-DRD with Segawa's syndrome, a point mutation in TH (Gln381Lys) resulted in a pronounced decrease in TH activity to about 15% of that of the wild type. Several missense mutations in the TH gene have been found in AR-DRD in Europe. The phenotype of AR-DRD with the Leu205Pro mutation in the TH gene, which produces a severe decrease in TH activity to 1.5% of that of the wild type, was severe, not dystonia/Segawa's syndrome, but early-onset parkinsonism. However, a marked improvement of all clinical symptoms with a low dose of L-dopa was reported in AR-DRD/parkinsonism patients. These findings on DRD indicate that the nigrostriatal DA neurons may be most susceptible to the decreases in GCH1 activity, BH4 level, TH activity, and DA level, and that DRD is the DA deficiency without neuronal death in contrast to juvenile parkinsonism or Parkinson's disease with DA cell death.

A novel mutation in the GTP cyclohydrolase I gene associated with a broad range of clinical presentations in a family with autosomal dominant dopa-responsive dystonia

We examined a large family of Ashkenazi Jewish origin with autosomal dominant dopa-responsive dystonia (DRD). Mutation analysis of the GTP cyclohydrolase I gene revealed in affected members a novel point mutation (a C/A change in exon 1) resulting in a threonine-to-lysine substitution at residue 94. The mutation was characterized by variable expressivity and was associated with either a 'classical' DRD phenotype or various atypical phenotypes, such as subtle transitory equinovarus postures of the feet or isolated hand tremor. This observation demonstrates the significance of the molecular testing in establishing the clinical diagnosis of DRD.