Molecular characterization of 6-pyruvoyl-tetrahydropterin synthase deficiency in Japanese patients

We identified three mutations in four Japanese patients with central type 6 -pyruvoyl-tetrahydropterin synthase (PTPS) deficiency. One missense mutatio n was a C-to-T transition, resulting in the substitution of Pro by Ser at c odon 87 (P87S) in exon 5. Another missense mutation was a G-to-A transition , resulting in the substitution of Asp by Asn at codon 96 (D96N) in exon 5. A splicing mutation was found by skipping of exon 4 on PTPS mRNA analysis, and a G-to-A transition at the third base of codon 81 (E81E) and at the te rminal base in exon 4 were detected on genomic PTPS DNA analysis. The E81E mutation affected the splice donor site of exon 3 and caused the splicing e rror. In COS cell expression analysis, the P87S and D96N mutant constructs revealed, respectively, 52% and 10% of wildtype activity. Patients with P87 S/P87S (52%/52% in-vitro PTPS activity) exhibited 0.11 and 0 mu U/g hemoglo bin [Hb] in erythrocyte PTPS activity (wild-type control: 11-29 mu U/gHb) e rythrocyte PTPS activity, and the patient with P87S/D96N mutations (52%/10% ) had 0.97 mu U/gHb in PTPS erythrocyte activity. The PTPS erythrocyte acti vity did not coincide with the in-vitro PTPS activity based on patient geno type.