Autosomal dominantly inherited defects in the GTPCH gene (GCH1) cause a form of dystonia that is responsive to treatment with levodopa (dopa-responsive dystonia [DRD]).
Loss-of-function mutations in GCH1 result in severe reduction of dopamine synthesis in nigrostriatal cells and are the most common cause of DOPA-responsive dystonia, a rare disease that classically presents in childhood with generalized dystonia and a dramatic long-lasting response to levodopa.
Dopa-responsive dystonia in children, including guanosine triphosphate cyclohydrolase I deficiency, is an important subcategory of treatable dystonia characterized by a dramatic, sustained response to levodopa.
Dopa-responsive dystonia (DRD) is a rare form of hereditary movement disorder with onset in childhood, characterized by gait difficulties due to postural dystonia with marked improvement after low doses of levodopa.
Three had onset in infancy with delayed sitting and walking before the appearance of overt dystonia; infantile onset is infrequent in dopa-responsive dystonia.
Similarly, there has been progress in our understanding of the genetic underpinnings of the "dystonia-plus" syndromes: dopa-responsive dystonia (DRD), myoclonus-dystonia (M-D), and rapid-onset dystonia-parkinsonism (RDP).
Analysis of a large kindred with dopa-responsive dystonia, using this new polymorphism and conventional RFLPs for the 9q32-34 region, excludes loci in this region as a cause of this form of dystonia.
Herein, we investigated the frequency of GCH1 mutations in a series of 53 familial EOPD patients (21 with dystonia) and screened them for mutations in PRKN, PINK1, and DJ-1.
Patients with the dystonia plus syndrome DYT5 display levodopa-responsive dystonia sometimes associated with tremor or parkinsonism (DYT5a, mutations in GCH1); a more severe phenotype with psychomotor involvement can be seen in recessive forms (DYT5b with TH mutations, SPR-deficiency syndrome).
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.
In contrast, no mutations in any exons of the GTP-CH I gene were found in 2 patients with early-onset parkinsonism with dystonia (EOP-D) who developed dopa-responsive parkinsonism and dystonia at 6 and 8 years old, respectively.
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.