The Neandertal Progesterone Receptor
The hormone progesterone is important for preparing the uterine lining for egg implantation and in maintaining the early stages of pregnancy. The gene encoding the progesterone receptor (PGR) carries introgressed Neandertal haplotypes with two non-synonymous substitutions and a mobile Alu element. They have reached nearly 20% frequency in non-Africans and have been associated with preterm birth. Here we show that whereas one of the missense substitutions appears fixed among Neandertals, the other substitution as well as the Alu insertion were polymorphic among Neandertals. We show that two Neandertal haplotypes carrying the PGR gene entered the modern human population and that present-day carriers of the Neandertal haplotypes express higher levels of the receptor. In a cohort of present-day Britons, these carriers have more siblings, fewer miscarriages and less bleeding during early pregnancy suggesting that it promotes fertility. This may explain the high frequency of the Neandertal progesterone receptor alleles in modern human populations.