Are would-be parents carrying a genetic risk of serious illnesses that they could potentially pass on to their children? In the USA, doctors recommend that couples have genetic screening before trying to conceive. Researchers at the University of Zurich have now shown that a maximal variant of this test detects the risk in 44 percent of couples who are related by blood, and in just 5 percent of other couples. Non-hereditary newly acquired mutations are a major reason for the reduced detection rate in the latter.