DNA POLYMORPHISMS IN THE LACTASE GENE - LINKAGE DISEQUILIBRIUM ACROSSTHE 70-KB REGION

The enzyme lactase, which is responsible for the digestion of dietary lactose, is present in the intestine of some adults but not others. As a means of providing a platform to explore the molecular basis of thi s nutritionally relevant genetic variation we have screened for polymo rphism in several regions of the lactase gene. In each case simple pol ymerase chain reaction-based procedures (including single-strand confo rmation analysis and denaturing gradient gel electrophoresis) were use d, combined with silver staining as a method of detection. Allelic var iation was found at 6 different sites. One previously published polymo rphism was also tested. The frequencies of the alleles were determined in more than 100 unrelated individuals of the Centre d'Etude du Polym orphisme Humain (CEPH) panel, and the haplotypes were deduced. A regio n of linkage disequilibrium was observed, which spans the whole coding region of the lactase gene(similar to 60-70 kb); there were only 3 co mmon haplotypes in this population. When the CEPH sample was subdivide d according to the population of origin (France or Utah) the haplotype frequencies were shown to be markedly different.