Cold Sore Linked to Mutation in gene:

 

Cold sores affect around one in five people but, until now, no one has been sure why some are more prone to the virus that causes them.
Researchers at the University of Edinburgh have found that people affected by cold sores have a mutation in a gene, which means their immune system is not able to prevent them from developing.
Cold sores are caused by a strain of the herpes simplex virus — herpes simplex virus type 1 (HSV-1). Between 80 and 90 per cent of people are infected with the virus, but only about a quarter of them get frequent cold sores.