Relatives of people diagnosed with a defect that can cause early heart attacks are to be screened to see if they are also at risk.
The National Institute for Health and Clinical Excellence (NICE) said experts hope to identify up to 100,000 people with familial hypercholesterolaemia (FH), a genetic defect that causes high cholesterol.
The condition speeds up a process that causes the narrowing of arteries, putting people at higher risk of heart attacks.
If left untreated, half of men with FH will have a heart attack by the age of 50 and a third of women will have one by the age of 60.
About 15,000 people in the UK are known to have FH, but health experts think about 95,000 more people are undiagnosed.
The gene is passed on in families and the plan is to screen first-degree relatives - parents, siblings and children - of those known to have FH.
NICE recommends "cascade testing" of at-risk people in England. Doctors are being urged to screen as many of these first-degree relatives as possible and NICE expects at least 50,000 will be identified as having FH as a result of the plan.