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Dopa-responsive dystonia is characterized by childhood onset and a dramatic response to treatment with a low dose of levodopa. The condition is most commonly caused by mutations in the gene for GTP-cyclohydrolase 1 (GCH1), and less often by mutations in the genes for tyrosine hydroxylase (TH) or sepiapterin reductase (SPR) — all enzymes critical for dopamine synthesis. To study the relative frequencies of mutations in these genes and to determine the clinical spectrum associated with these mutations, investigators analyzed DNA from a series of patients with dopa-responsive dystonia.
The authors studied 64 unrelated index patients who presented with childhood-onset dystonia that improved by at least 50% after treatment with levodopa. Forty-se…