Structure of human holocarboxylase synthetase gene and mutation spectrum of holocarboxylase synthetase deficiency

Holocarboxylase synthetase (HLCS) is an enzyme that catalyzes the incorpora tion of biotin into apo-carboxylases, and its deficiency causes biotin-resp onsive multiple carboxylase deficiency. The reported sequences of cDNA for human HLCS from liver. lymphocyte, and KG-1 myeloid cell lines differ at th eir 5' regions. To elucidate variations of the human HLCS mRNA and longer 5 ' cDNA ends, we performed screening of the human liver cDNA library and rap id amplification of the cDNA ends (RACE). Our results suggest the existence of three types of HLCS mRNA that start at different exons. The first type starts at exon 1. and the second type starts at exon 3. and both are found in various human tissues. The third type, corresponding to the cDNA from th e KG-I cell. starts at exon 2 of the HLCS gene. Various splicing patterns f rom exons 3-6 were also observed. None of the variations of cDNA found crea ted a new initiation codon. Mutation screening from exons 6-14, therefore, was sufficient to detect amino acid changes in HLCS in patients. Our direct sequencing strategy for screening mutations in the HLCS gene revealed muta tions in five Japanese patients and seven non-Japanese patients. Our analys es involving 12 Japanese and 13 non-Japanese patients and studies by others indicate that (1) there is no panethnically prevalent mutation; (2) the Ar g508Trp, Gly581Ser, and Val550Met mutations are found in both Japanese and non-Japanese populations; (3) the IVSIO+5G -->A mutation is predominant and probably a founder mutation in European patients; (4) the 655-656insA, Leu 237Pro, and 780delG mutations are unique in Japanese patients; (5) the spec trum of the mutations in the HLCS gene may vary substantially among differe nt ethnic groups.