A private company that leads the market in genetic testing for breast cancer genetic mutations has refused to share information that could help patients, experts have charged.

Myriad Genetics, based in Salt Lake City, Utah, owns patents that make it the monopoly provider in the United States of tests for BRCA1 and BRCA2, two genetic variants that predispose women to breast cancer. It has conducted nearly a million tests and built up databases that give it unrivalled power to analyse the results, especially when they show mutations whose significance is uncertain.

When Myriad finds such a mutation, it offers free testing to family members, building up the database and enhancing its ability to assess the importance of “variants of unknown significance” (VUS).

In a paper in the European Journal of Human Genetics a team led by Robert Cook-Deegan of Duke University …