Search

Dominantly inherited guanosine triphosphate (GTP)-cyclohydrolase deficiency, otherwise known as Segawa's disease or dopa-responsive dystonia, has a wide spectrum of phenotypic expression ranging from asymptomatic to very severe. Penetrance is more frequent in women as compared with men, and there is a variable occurrence of diurnal variation in symptom intensity. Biochemical characterization of the disease has demonstrated lower cerebrospinal fluid levels of tetrahydrobiopterin (BH4), neopterin, and homovanillic acid and low levels of tyrosine hydroxylase protein in the striatum. To investigate the pathophysiology, we have begun to characterize biogenic amine and BH4 metabolism in the GTP cyclohydrolase deficient hph-1 mouse. The data show low brain levels of BH4, catecholamines, serotonin, and their metabolites together with low levels of tyrosine hydroxylase protein within the striatum. The hph-1 mouse therefore provides a good model system in which to study the human disease.

Mutations in the GTP-cyclohydrolase I (GCH) gene have been identified as a cause of two disorders: autosomal dominant hereditary progressive dystonia/dopa-responsive dystonia (HPD/DRD) and autosomal recessive GCH-deficient hyperphenylalaninemia (HPA). Detailed clinical descriptions and genetic analysis of patients with phenotypes intermediate between HPD/DRD (mild) and GCH-deficient HPA (severe) have not been reported. We conducted genomic DNA sequencing of the GCH gene in two patients (Cases 1 and 2) manifesting generalized dystonia responsive to levodopa and severe developmental motor delay. In the pedigree of Patient 1, there were HPD/DRD patients in three generations preceding the index case. Patients 1 and 2 were compound heterozygotes with maternally and paternally transmitted mutations in the coding region of the GCH gene. In both compound heterozygotes, tetrahydrobiopterin (BH4) levels in cerebrospinal fluid were lower than those in HPD/DRD. Administration of BH4, in addition to levodopa, further improved the symptomatology of Patient 1. Our data demonstrate a new phenotype of GCH deficiency associated with compound heterozygosity for GCH gene mutations and suggest the usefulness of combined BH4 and levodopa therapy for this disorder.

We report cerebrospinal fluid monoamine metabolite analyses and 6-[18F]fluoro-1-dopa positron emission tomography (FD-PET) from an asymptomatic carrier of the gene for dopa-responsive dystonia. Cerebrospinal fluid homovanillic acid, tetrahydrobiopterin, and neopterin concentrations were reduced in this man and in his affected children. His FD-PET was normal, as we have previously found in dopa-responsive dystonia. Neurological function and FD-PET may be normal despite marked abnormality in dopamine metabolism.

Three children, 2 of them siblings, developed a progressive dystonic condition in the first decade of life. The symptoms and signs were milder in the mornings or after a daytime nap but worsened greatly later in the day. One patient became unable to walk by evening. Investigations in 2 patients revealed a reduced concentration of cerebrospinal fluid homovanillic acid. The 2 more severely affected patients showed dramatic and sustained improvement with levodopa therapy. The condition bears a clinical resemblance to some reported cases of juvenile Parkinson's disease but is probably a separate disorder.