When is a mutation not a mutation: the case of the c.594-2A>C splice variant in a woman harbouring another BRCA1 mutation in trans.

Since the identification of BRCA1 there has only ever been described two bi-allelic mutation carriers, one of whom was subsequently shown to be a mono-allelic carrier. The second patient diagnosed with two BRCA1 mutations appears to be accurate but there remain some questions about the missense variant identified in that patient.