MUTATION IN THE EXON-10 (R173W) OF THE HYDROXYMETHYLBILANE SYNTHASE GENE IN 2 UNRELATED JAPANESE FAMILIES WITH ACUTE INTERMITTENT PORPHYRIA

Acute intermittent porphyria (AIP) is an inherited disorder characteri zed by a deficiency of hydroxymethylbilane synthase (EC 4.3.1.8.; HMBS ), the third enzyme in the heme biosynthetic pathway. To date, 113 dif ferent HMBS gene mutations have been reported in the world. However, t here were a few reports of the gene mutations in the Japanese AIP pati ents. We studied the gene mutation in two unrelated AIP families in th e San-in district, a local area of Western Japan. The overlapping 6 fr agments of the HMBS gene, amplified by the reverse transcript-polymera se chain reaction, were analyzed by the single-strand conformation pol ymorphism with silver staining technique. The abnormal fragment from a member of one family was sequenced to detect the C to T substitution at 517 nucleic acid position of cDNA, which led to a missense mutation of arginine to tryptophan exchange at an amino acid level (R173W). Th is mutation located in exon 10 created a new site of the MSP 1 restric tion endonuclease and was screened by the amplified fragment of exon 1 0 from genomic DNA with the MSP 1 digestion. The mutaion was detected totally in three members of the family and interestingly also in two p atients of an unrelated family. This mutation has been reported widely in the world independently, such as in a Swedish, a Canadian, a Finni sh, and a French family, but is the first in Japanese patients. The sc reening method for this mutation is useful for diagnosis in Japanese A IP patients.