Sharing at the major histocompatibility complex affects the secondary sex ratio in differing ways

Detection of intergenerational genetic effects with application to HLA-B matching as a risk factor for schizophrenia

BACKGROUND AND METHODS

Association studies using unrelated individuals cannot detect intergenerational genetic effects contributing to disease. To detect these effects, we improve the extended maternal-fetal genotype (EMFG) incompatibility test to estimate any combination of maternal effects, offspring effects, and their interactions at polymorphic loci or multiple SNPs, using any size pedigrees. We explore the advantages of using extended pedigrees rather than nuclear families. We apply our methods to schizophrenia pedigrees to investigate whether the previously associated mother-daughter HLA-B matching is a genuine risk or the result of bias.

RESULTS

Simulations demonstrate that using the EMFG test with extended pedigrees increases power and precision, while partitioning extended pedigrees into nuclear families can underestimate intergenerational effects. Application to actual data demonstrates that mother-daughter HLA-B matching remains a schizophrenia risk factor. Furthermore, ascertainment and mate selection biases cannot by themselves explain the observed HLA-B matching and schizophrenia association.

CONCLUSIONS

Our results demonstrate the power of the EMFG test to examine intergenerational genetic effects, highlight the importance of pedigree rather than case/control or case-mother/control-mother designs, illustrate that pedigrees provide a means to examine alternative, non-causal mechanisms, and they strongly support the hypothesis that HLA-B matching is causally involved in the etiology of schizophrenia in females.

MHC class II DRB diversity, selection pattern and population structure in a neotropical bat species, Noctilio albiventris

Genes of the major histocompatibility complex (MHC) have a crucial role in the immune response of vertebrates, alter the individual odour and are involved in shaping mating preferences. Pathogen-mediated selection, sexual selection and maternal-fetal interactions have been proposed as the main drivers of frequently observed high levels of polymorphism in functionally important parts of the MHC. Bats constitute the second largest mammalian order and have recently emerged as important vectors of infectious diseases. In addition, Chiroptera are interesting study subjects in evolutionary ecology in the context of olfactory communication, mate choice and associated fitness benefits. Thus, it is surprising that they belong to the least studied mammalian taxa in terms of their MHC diversity. In this study, we investigated the variability in the functionally important MHC class II gene DRB, evidence for selection and population structure in the group-living lesser bulldog bat, Noctilio albiventris, in Panama. We found a single expressed, polymorphic Noal-DRB gene. The substitution pattern of the nucleotide sequences of the 18 detected alleles provided evidence for positive selection acting above the evolutionary history of the species in shaping MHC diversity. Roosting colonies were not genetically differentiated but females showed lower levels of heterozygosity than males, which might be a sign that the sexes differ in the selection pressures acting on the MHC. This study provides the prerequisites for further investigations of the role of the individual MHC constitution in parasite resistance, olfactory communication and mate choice in N. albiventris and other bats.

A study of natural killer cell lectin-like receptor K1 gene (KLRK1/NKG2D) region polymorphisms in a European population sample

Recent evidence has reinforced the belief in immunosurveillance as a powerful mechanism against cancer development. The natural killer (NK) cell has been recognized as a potent agent of cancer immunosurveillance. A Japanese cohort study correlated natural cytotoxic activity levels with subsequent cancer development and identified NK cell lectin-like receptor K1 gene (KLRK1/NKG2D) polymorphisms as genetic markers of cancer predisposition. In the present study, we genotyped 82 reference cell lines and 388 newborn samples at 10 KLRK1 region variants by TaqMan((R)) allelic discrimination assays and showed that the same polymorphisms occur at similar frequencies in Europeans. The same haplotype block that has been associated with lower natural cytotoxic activity also occurred with the highest frequency in our sample. We further detected evidence suggestive of natural selection at some of the loci analyzed and more importantly, sex specificity of this selection. It appeared that heterozygosity at loci forming a haplotype block was unfavorable for boys. Given the relevance of NK cells in fetal survival, this finding has potential implications in the study of genetics of maternofetal recognition. Our preliminary findings are of marginal statistical significance and should be replicated in a larger sample. We believe that our results will increase awareness of the involvement of KLRK1 in cancer immunosurveillance and possibly in prenatal selection.