Foeto-maternal compatibility in HLA-DR, -DQ, and -DP loci in Finnish couples suffering from recurrent spontaneous abortions.

The polymorphism of Major Histocompatibility Complex (MHC) class II genes DRB, DQA, DQB, and DPA was studied by TaqI Restriction Fragment Length Polymorphism (RFLP) in recurrent spontaneous abortions (RSA). The study group consisted of 35 primary abortion (PA) couples (no children) and 15 secondary abortion (SA) couples (1-2 children before abortions). We found no increase in DR-DQ compatibility between the mother and the foetus in the Finnish RSA group. In contrast to findings in some other populations, foeto-maternal incompatibility was increased in the PA group. Thus, our results do not support the theory that increased MHC class II compatibility is a cause of abortions as such. The Finns are a small and relatively isolated population with a unique gene inheritance. Thus, one can speculate that, if the human MHC class II is in the linkage with disadvantageous 'fertility genes', and these genes might nonetheless still be clustered in only a few MHC haplotypes among the Finns. This would be the reason, that DR-DQ sharing is not seen. The presence of rare HLA alleles, such as DR2 and DR6, among the aborters also supports this. In addition, this study extends our previous findings on MHC class III in regards to PA and SA couples differing immunogenetically from each other. In MHC class II, this was most obvious in the DPA1 locus. The vast majority of SA women were heterozygous for the two most common DPA1 alleles (14.0 kb and 13.5 kb), resulting in significantly smaller chances for a DPA1 mismatched foetus to occur in the SA group than in the controls or in the PA women.