Which movement disorder is described as involuntary movements in young children, slowly progressive, with a diurnal pattern and responsive to small doses of levodopa?

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Dopamine-responsive dystonia presents in childhood with gradually progressive dystonic movements, often starting in the legs, and shows a clear diurnal pattern—worse later in the day and improved with sleep—along with a dramatic response to very small doses of levodopa. This combination points to a defect in dopamine synthesis that is exquisitely dopamine-responsive, commonly due to GCH1 mutations. In contrast, athetosis involves slow, writhing movements; chorea involves rapid, irregular, dance-like movements; and choreoathetosis mixes those features. Those patterns don’t typically pair with the marked diurnal variation and strong levodopa responsiveness seen here, making dopamine-responsive dystonia the best fit.