Several other studies show that variation in the CYP19 gene is unlikely to be responsible for PCOS by investigating both a tetranucleotide repeat (TTTA) polymorphism in intron 4 (the different numbers of tetranucleotide TTTA repeats in intron 4 are associated with increased risk for breast cancer) and the promoter of the CYP19 gene [12,20,21]. The gene discussed is CYP19A1; the disease is polycystic ovary syndrome.