Cloning of the holocarboxylase synthetase cDNA and identification of mutations prevalent in Japanese HCS-deficient patients

Holocarboxylase synthetase (HCS) plays an essential role in biotin utilization in cells and its deficiency causes biotin-responsive multiple carboxylase deficiency in humans. We have cloned the human HCS cDNA, which maps to chromosome 21q22.1. Two mutations in the HCS genes of Japanese patients with HCS deficiency have been identified: a transition from T to C which causes an amino acid substitution of proline for leucine at position 237 (L237P) and A single guanine base deletion (delta G1067) followed by premature termination. Transient expression in cultured fibroblasts from a patient after site-directed mutagenesis showed that the L237P mutation was responsible for decreased HCS activity. Hybridization analysis using allele-specific oligonucleotide probes demonstrated that the prevalence of the mutations--L237P and delta G1067--was 50% and 30%, respectively, among Japanese patients with HCS deficiency.