A population genomic analysis of genetic markers associated to Twinning susceptibility in humans

Abstract

Spontaneous dizygotic (DZ) twinning is a complex trait with an important contribution from environmental factors and genetic disposition. Twin births is a common event with a worldwide incidence that suppose distinct health implications for mother and child, occasionally assuming an enormous risk. Since twinning can present both advantages and disadvantages, it is interesting to carry out an evolutionary study of the risk variants involved in order to better understand the presence of this trait in present-day society. We have studied with the help of the first reported GWAS meta-analysis of twin alleles the evolution of risk alleles associated to twinning, focusing on the European population using archaic, ancient and modern human samples. Here, we demonstrate that there is no evolutionary trend for the variants associated to twinning until the last 2000 years, where we reported a negative selection event over the risk allele. We also confirm that Neandertal introgressed variants are enriched for the risk allele in human modern genome and, even more, the size of the haplotype has provided us information of the selective pressures suffered by these regions, exposed by a fragment size decrease for introgressed haplotypes related to the protective allele of the twin trait. This study suggest that twin phenotype has been subjected to different series of selective pressures since ancient times. Twinning maybe was an advantageous factor in past times, but nowadays the evolution is acting against this phenotype.