Biallelic variants in BRCA1 were traditionally believed to either be embryonically lethal, or a rare cause of Fanconi anaemia; however, increasing numbers of cases are being reported with phenotypes which overlap between Fanconi anaemia and other chromosome instability syndromes, particularly Nijmegen Breakage Syndrome; this has an associated risk of early-onset breast and/or ovarian cancer predisposition [113,114,115,116]. This evidence concerns the gene BRCA1 and ovarian cancer.