The London Bridge Clinic, a UK fertility clinic, is to offer a US genetic test that promises to eliminate the chances of a couple having a baby with any of over 100 inherited diseases. The saliva test, developed by US company Counsyl, will be launched by the clinic over the next few weeks. It is already offered at several fertility clinics in the USA. At £700 per couple, the test screens for common mutations in 109 genes, which cause conditions such as cystic fi brosis, muscular dystrophy and sickle cell anaemia. Those diseases affect one in 208 live births.

The test will not prevent a couple from having a child with an inherited disease. What it does is to detect whether the male and female partner carry recessive mutations. If each partner carries a recessive mutation, there is a 25% chance that their child will inherit both copies of the mutation and have the given disease. Options for a positive-testing couple include sperm or egg donation.