When the parents are also first cousins

New evidence suggests offspring are more likely to have mental health problems
kissing cousins

Children of first cousins are more likely to be depressed or suffer psychosis than children of non-related parents, research shows.

While it is well known that the progeny of consanguineous couples are at elevated risk for a wide range of medical problems, it has only now been demonstrated that they are also at risk of serious common psychiatric disorders.