Teaching Video NeuroImages: Paroxysmal hyperkinesia with diurnal fluctuations due to sepiapterin-reductase deficiency

A 42-year-old man, born of consanguineous parents, presented with long-standing severe, nonepileptic jerky movements of the upper body, pronounced during the second half of the day and improving after sleep (video, A and B). There was a history of neurodevelopmental disorder with axial hypotonia, delayed milestones, intellectual disability, and poor speech production. The combination of a neurodevelopmental syndrome and a movement disorder with diurnal fluctuations(1)led to targeted exome sequencing for monoamine metabolism disorders. A homozygous nonsense variant in theSPRgene was identified (figure), confirmed by Sanger sequencing (figure). Treatment with levodopa led to marked improvement of abnormal movements (video, C).