Are birthmarks genetic?

While a few birthmarks are hereditary and run in families, most are not. Very rarely, some birthmarks are caused by gene mutations. For instance, some babies born with port-wine stains have a rare condition called Klippel-Trenaunay syndrome. This syndrome is caused by a genetic mutation that is not generally inherited. Another rare condition, Sturge-Weber syndrome, also appears as port-wine birthmarks and is caused by a different gene mutation. It also doesn’t run in families and can’t be inherited.