We herein report on a woman who developed breast cancer at an early age with no developmental delay who was referred to our laboratory for genetic testing and subsequent follow-up studies since she was shown to harbouran unequivocal BRCA1 mutation and a splice site mutation in trans, both of which are predicted to result in the absence of functional full-length wildtype BRCA1. This evidence concerns the gene BRCA1 and breast carcinoma.