Genotype-phenotype correlations in sepiapterin reductase deficiency. A splicing defect accounts for a new phenotypic variant.

Sepiapterin reductase (SR) catalyzes the final step in the de novo synthesis of tetrahydrobiopterin, essential cofactor for phenylalanine, tyrosine, and tryptophan hydroxylases. SR deficiency is a very rare disease resulting in monoamine neurotransmitter depletion. Most patients present with clinical symptoms before the first year of age corresponding to a dopa-responsive dystonia phenotype with diurnal fluctuations, although some patients exhibit more complex motor and neurological phenotypes.