A charity has called on the NHS to review its DNA screening guidelines for breast cancer risk genes after a new study suggested more than half of potential cases are being missed among Ashkenazi women.

Ashkenazi Jews are one of a number of high risk groups likely to carry a mutation of the BRCA1 and BRCA2 gene which increases the risk of developing breast and ovarian cancers.

In the wider population one in 800 people carry the BRCA mutation; for Ashkenazi Jews it is one in 40.

The University College London study tested 1,034 Ashkenazi women for the gene, half of whom had a family history of cancer.

The results showed mutation genes in 56 per cent of those who did not have a history of cancer in their family.

Under current NHS guidelines the women would not have been offered the test.

Professor Ian Jacobs, who ran the trial, said: "The NHS will of course need to do their own careful analysis, but it deserves at least a re-assessment. They need to think about how to make the test available to Ashkenazi Jews in a systematic way."

Athena Lamnisos, chief executive of The Eve Appeal, which funded the study, said: "There is a different approach that can be taken on BRCA gene screenings that picks up more women and doesn't create a big psychological impact."

Women who discover they are carriers of the mutated gene can opt for preventative surgery. Caroline Presho, 37, found out she was a carrier after initially being refused NHS testing because she did not meet the criteria. She had a double mastectomy and had her ovaries removed.

"Being armed with information means people can make lifestyle choices," she said. "It would save the NHS money. Instead of treating cancer after the fact they would be giving people the choice of having risk-reducing surgery."

But Lisa Steele, Chai Cancer Care chief executive, urged caution: "The psychological impact was only measured seven days and three months after participants received the results.

"The effects can hit much later. Sometimes people come to us six months after cancer treatment.

"It doesn't feel it has been long enough to test the psychological impact."

The NHS said it would "further assess and evaluate the evidence" from the "very interesting study".