Segawa disease, caused by autosomal dominant GTP cyclohydrolase I (GTPCHI) deficiency from mutations in the GCHI gene [6], is the most frequent condition that manifests as DRD, whereas fewer cases are described for deficiencies in sepiapterin reductase (SR) [7], 6-pyruvoyl tetrahydrobiopterin synthase (PTPS) [8], and TH [2,9]. This evidence concerns the gene TH and dystonia 5.