A RARE NEUTRAL POLYMORPHISM IN 21-HYDROXYLASE GENES AS HLA HAPLOTYPE MARKER - EVIDENCE FOR STRONG FOUNDER EFFECT IN THE FINNISH POPULATION

The usefulness of rare neutral gene polymorphisms as an HLA haplotype marker and as a probe for founder effect in small populations was test ed by determining the frequency and MHC associations of an NcoI polymo rphism in the P450c21 genes in the Finnish population. In the general population, 13% (9 of 70) of samples had the NcoI site. A very strong association with the HLA-B62, Bf()F, C4A(*)3, C4B(*)Q0, DRB1(*)13, DQ A10103, DQB1(*)0603 alleles was observed. P450c21A and P450c21B gene- specific amplifications mapped the polymorphic site to both P450c21A p seudogene and P450c21B functional gene of this haplotype in all cases. The majority of haplotypes with the NcoI cutting site found in this p opulation may thus have derived from a single ancestral haplotype. The HLA homozygous cell lines with the NcoI site showed heterogeneous HLA associations. Our results suggest that in small populations the varie ty of MHC haplotypes may be surprisingly low and rare polymorphisms ca n serve as informative markers.