(LIveScience) - A single genetic mutation is the cause of "port wine" birthmarks, as well as a rare neurological condition of which the birthmarks are a distinctive feature, researchers have discovered.

The mutation occurs after conception — it is not present in sperm or egg cells — but exactly when it occurs could determine whether a baby develops only a birthmark, or the serious neurological disorder Sturge-Weber syndrome, the researchers say. People with this disorder have port wine birthmarks (reddish to purplish discolorations), typically on the face, and also can suffer seizures, paralysis, blindness and learning disabilities. Finding the genetic cause of Sturge-Weber syndrome and port wine birthmarks is the first step in developing new treatments for the conditions, the researchers said.

Finding the genetic cause of Sturge-Weber syndrome and port wine birthmarks is the first step in developing new treatments for the conditions, the researchers sa