Recessive forms of DRD have also been identified with mutations in the genes for tyrosine hydroxylase (TH), 6-pyruvoyl-tetrahydropterin synthase (PTPS), sepiapterin reductase (SR), dihydropteridine reductase (DHPR) and aromatic acid decarboxylase (AADC). This evidence concerns the gene QDPR and dystonia 5.