Japanese triplets with cerebrotendinous xanthomatosis are homozygous for a mutant gene coding for the sterol 27-hydroxylase (Arg441Trp).

We present the first case of triplets with cerebrotendinous xanthomatosis (CTX). A C-to-T base change identified in the genomic DNA and cDNA encoding the sterol 27-hydroxylase led to replacement of arginine by tryptophan at position 441 (Arg441Trp) in the triplets. The triplets were homozygous and their mother was heterozygous for this mutant gene. The triplets exhibited an identical phenotypic expression, which was different from that of a sporadic CTX case with the same mutation.