MOLECULAR ANALYSIS OF DIHYDROPTERIDINE REDUCTASE DEFICIENCY - IDENTIFICATION OF 2 NOVEL MUTATIONS IN JAPANESE PATIENTS

Mutations in the dihydropteridine reductase (DHPR) gene result in hype rphenylalaninaemia and deficiency of various neurotransmitters in the central nervous system, causing severe neurological symptoms. We studi ed two Japanese patients with DHPR deficiency and identified a missens e and a splicing error mutation, respectively. A homozygous missense m utation (tryptophan(36)-to-arginine) was detected in patient 1. The mu tation abolished DHPR activity according to in vitro expression studie s. The DHPR mRNA in patient 2 was markedly decreased. Reverse transcri ption-polymerase chain reaction of the mRNA generated a cDNA fragment with a 152-bp insertion. The inserted sequence contained a termination codon, which was likely to affect the stability of the mRNA. Analysis of genomic DNA showed that the insertion was derived from putative in tron 3 of the DHPR gene, and an intronic A-to-G substitution was prese nt adjacent to the 3'-end of the inserted sequence. The nucleotide cha nge generated a sequence similar to an RNA splice donor site and proba bly activated an upstream cryptic acceptor site, thus producing an abn ormal extra exon.