Dopa-responsive hypersomnia and mixed movement disorder due to sepiapterin reductase deficiency

Sepiapterin reductase deficiency (SRD) is a rare, treatable disorder of monoamine metabolism with cognitive delay and L-dopa responsive movement disorder. We describe a patient with SRD and distinctive phenotypic feature of marked hypersomnolence. Our patient showed improvement with therapies directed at both serotonergic and dopaminergic deficiencies. This case illustrates symptoms that characterize the SRD phenotype and demonstrates the importance of systematic treatment trials addressing the various biochemical abnormalities present.