In fact, only about 2 per cent of inherited breast cancers are due to the faulty BRCA genes that are traditionally tested for, according to Professor Gareth Evans, a consultant in medical genetics at Manchester University.
‘There are an additional seven moderate to high-risk genes, and hundreds of others which, in combination, may increase the risk of developing the disease.’ However, he says: ‘Even if a gene is identified, a daughter would have a lower risk than the mother because there is only a 50 per cent chance she has inherited it’.
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Professor Evans’s research has found that when women with a strong family history of breast cancer do not have the faulty BRCA gene, they often instead have a pattern of small gene fragments — also known as single nucleotide polymorphisms (or SNPs) — that increase their risk.
The research, published in the Journal of Medical Genetics in 2017, suggests that each mutation individually had minimal effect; but, combined, they could increase or decrease the breast cancer risk considerably.