Men who inherit a rare genetic mutation are 10 to 20 times more likely than average to develop prostate cancer, a study has found. The gene variant may help explain cases of the disease that run in families and strike men at unusually young ages. Scientists believe the discovery could pave the way to a genetic test for inherited prostate cancer. A study of more than 5,000 men treated for prostate cancer found that 1.4 percent carried the defective \"HOXB13 gene\". Men with the mutation were much more likely to have a father or brother diagnosed with the disease. It is the first major genetic variant to be associated with prostate cancer. Professor William Isaacs, from Johns Hopkins University School of Medicine, a member of the US team, said, \"It\'s what we\'ve been looking for over the past 20 years. \"It\'s long been clear that prostate cancer can run in families, but pinpointing the underlying genetic basis has been challenging and previous (studies) have provided inconsistent results.\" First indications of the gene variant came from a study of samples of young men with prostate cancer from 94 families with a history of the disease. Members of four different families had the same mutation in the HOXB13 gene, which plays a key role in the development and function of the prostate gland. The findings were published in the New England Journal of Medicine and highlighted by the British media Thursday. \"We need to continue studying this variant and look at larger groups of men, \" said Prof Isaacs. \"Our next step will be to develop a mouse model with this mutation to see if it causes prostate cancer.\"