Because not all GCH-1 deficient DRD patients have GCH-1 mutations in the gene’s coding region or in the splice sites, which are detectable by current genomic DNA sequencing of the GCH-1 gene [50], and because of the high occurrence of sporadic mutations in this gene [51], DNA testing for the autosomal dominant DRD is not suitable for routine clinical practice and must be complemented by enzymatic tests. Here, GCH1 is linked to dystonia 5.