IDENTIFICATION OF POLYMORPHISMS AND SEQUENCE VARIANTS IN THE HUMAN HOMOLOG OF THE MOUSE NATURAL RESISTANCE-ASSOCIATED MACROPHAGE PROTEIN GENE

The most common mycobacterial disease in humans is tuberculosis, and t here is evidence for genetic factors in susceptibility to tuberculosis . In the mouse, the Beg gene controls macrophage priming for activatio n and is a major gene for susceptibility to infection with mycobacteri a. A candidate gene for Beg was identified by positional cloning and w as designated ''natural resistance-associated macrophage protein gene' ' (Nramp1), and the human homologue (NRAMP1) has recently been cloned. Here we report on (1) the physical mapping of NRAMP1 close to VIL in chromosome region 2q35 by PCR analysis of somatic cell hybrids and YAC cloning and (2) the identification of nine sequence variants in NRAMP 1. Of the four variants in the coding region, there were two missense mutations and two silent substitutions. The missense mutations were a conservative alanine-to-valine substitution at codon 318 in exon 9 and an aspartic acid-to-asparagine substitution at codon 543 in the predi cted cytoplasmic tail of the NRAMP1 protein. A microsatellite was loca ted in the immediate 5' region of the gene, three variants were in int rons, and one variant was located in the 3' UTR. The allele frequencie s of each of the nine variants were determined in DNA samples of 60 Ca ucasians and 20 Asians. In addition, we have physically linked two hig hly polymorphic microsatellite markers, D2S104 and D2S173, to NRAMP1 o n a 1.5-Mb YAC contig. These molecular markers will be useful to asses s the role of NRAMP1 in susceptibility to tuberculosis and other macro phage-mediated diseases.