BRCA2 and cancer: BRCA1/2 act as tumor suppressor genes known to predispose the heterozygous carriers of deleterious mutations to breast, ovarian and other types of cancers (176) Conditional Brca2-deficient mice exhibit infertility due to defective follicular development and oocyte degeneration, whilst BRCA2 transcript may be found downregulated in human POI oocytes (177).