Holocarboxylase synthetase (HCS) deficiency is a rare autosomal recessive disorder of biotin metabolism. Including three new Japanese patients we diagnosed in this study, ten Japanese families have, so far, been accumulated. In these families, the mutations 237Leu > Pro (seven alleles) and 1067delG (five alleles) were predominant; 508Arg > Trp and 550Val > Met mutations were identified in three families in the heterozygous form and in one patient in the homozygous form, respectively. To determine the origin of these mutations, we identified new polymorphic microsatellite markers in the HCS gene and analyzed the haplotypes of the patients. All the 237Leu > Pro and the 1067delG alleles were associated with haplotype 2-2. This finding is consistent with the notion that these mutations are founder mutations in the Japanese population. Three Japanese 508Arg > Trp alleles were associated with several haplotypes, including 2-3 and 1-4. The haplotype of a Taiwanese patient homozygous for the 508Arg > Trp mutation was 2-3/2-3. The haplotype of one Japanese patient homozygous for the 550Val > Met mutation was 1-4/1-4, whereas that of a Jewish patient with the same homozygous mutation was 2-3/2-3. Both mutations were associated with at least two haplotypes and were found in several ethnic groups. The changes 508Arg > Trp and 550Val > Met occurred at CpG dinucleotide. The data suggest that these two mutations represent a mutational hot-spot.
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