The most common combination of alleles or haplotype (frequency 0.84, Figure 2) is associated with increased circulating FSH concentrations [37,44], increased frequency of dizygotic twinning [44], earlier age at menarche and menopause [23,31], shorter menstrual cycles, increased risk of endometriosis [27], and decreased risk of polycystic ovarian syndrome [45]. The gene discussed is BRD2; the disease is polycystic ovary syndrome.