“…It catalyzes the conversion of dihydroneopterin triphosphate to 6-pyruvoyltetrahydropterin [Nar et al, 1994;Ploom et al, 1999]. Patients with PTPS deficiency exhibit enzyme activity that is very low or absent in red blood cells (RBC) [Shintaku et al, 1988], or fibroblasts [Oppliger et al, 1997;Oppliger et al, 1995a,b], and is reduced to about 20% of controls in samples from obligate heterozygotes Scriver et al, 1987]. Enzyme activity is reported to be slightly higher in patients with the mild peripheral form than in those affected by the severe central form of PTPS deficiency.…”