Molecular genetic analysis of para-Bombay phenotypes in Hong Kong Chinese

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Molecular genetic analysis of para-Bombay phenotypes in Hong Kong Chinese


Author: Chee, Kit-yee
Title: Molecular genetic analysis of para-Bombay phenotypes in Hong Kong Chinese
Degree: M.Sc.
Year: 2000
Subject: Molecular genetics -- China -- Hong Kong
Chinese -- China -- Hong Kong
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Dept. of Nursing and Health Sciences
Pages: xi, 82 leaves : col. ill. ; 30 cm
Language: English
InnoPac Record:
Abstract: The para-Bombay phenotype (or H-deficient secretor) is a rare variant in the ABH system. This phenotype is characterised by a lack or a very weak expression of ABH antigens on red cells, but possesses them in secretion because of the absence of the H (FUT1) gene-encoded 帢(1,2)-fucosyltransferase and the presence of the Se (FUT2) gene-encoded 帢(1,2)-fucosyltransferase. This is the most common H-deficient phenotype found in Hong Kong Chinese with a frequency of 1 in 21,234. In this study, ABO genotyping and mutational analysis of both FUT1 and FUT2 genes were carried out for seven individuals who were serologically typed as para-Bombay. The samples were collected in a local hospital over a period of six years. As no relevant molecular genetic study has been performed on such rare phenotypes in local Hong Kong Chinese, it is worthwhile exploring the characteristics of and relationship between ABO, FUT1 and FUT2 genes of these phenotypes at the molecular level. With single-tube multiplex polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) analysis of the ABO gene, the ABO genotypes of the para-Bombay individuals under study were found to be BOl (2 individuals), BOlv (2), AlvB (1), AlvOl (1) and AlvAlv (1). The ABO genotypes correlated with the types of ABH substances found in their saliva. Three different null alleles, designated as h1, h2 and h3 were identified for the FUT1 gene by direct sequencing of its coding region. One new allele, h1, possessed a missense mutation C522A which changes phenylalanine to leucine at codon 174. The h2 allele lost one of the three AG repeats located at nucleotides 547-552 whereas two of the three T's located at nucleotides 880-882 were deleted in the h3 allele. Their FUT1 genotypes were h1h3 (1 individual), h2h3 (4), h2h2 (1), h3h3 (1). In other words, these para-Bombay individuals were either homozygous or compound heterozygous for the null alleles of the FUT1 gene. In addition, nested PCR followed by SSCP and DNA sequencing were performed on the FUT2 gene. The functional allele with C357T (Se357) and the null allele with C357T and A385T mutations (se357,385) were identified. C357T is a silent mutation while A385T is a missense mutation resulting in the substitution of phenylalanine for isoleucine at codon 129. One of the subjects was heterozygous for these two alleles while the others were homozygous for the Se357 allele. The fact that they carried at least one copy of a functional allele of the FUT2 gene was consistent with their status of being secretors. The Se357se357,385 individual had the genotype h1h3 at the FUT1 locus while the Se357Se357 individuals were either h2h3, h2h2 or h3h3. This indicates that there are three possible haplotypes across these two loci in the para-Bombay individuals under study: h1-se357,385, h2-Se357 and h3-Se357. Further molecular analysis of the FUT2 gene for 30 additional Chinese and 19 Caucasian normal samples revealed six new mutations including C29T, C278T, G685A, C894G, A895T and two C deletion at nucleotides 896-897. Twelve known mutations were also identified, they included A171G, C216T, C302T, C357T, A385T, G428A, C480T, G481A, G739A, A960G, G1009A and C1011T. These results suggest that for the FUT1 gene, the molecular basis of the para-Bombay phenotypes in Hong Kong Chinese was heterogeneous without any prevalent allele. The study of the FUT2 gene in both Chinese and Caucasian samples reveals extensive heterogeneity of the FUT2 alleles in different ethnic groups and demonstrates race specificity.

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