Inherited tandem duplication dup(X) (q131-q212) in a male proband

A tandem duplication dup(X) (q131-q212) has been diagnosed neonatally because of the peculiar appearance. Family investigation demonstrated that the duplication has segregated through phenotypically normal female carriers for at least three generations. Inactivation studies showed that the aberrant X was preferentially late replicating. The difficulties related to prenatal diagnosis of minor X chromosome aberrations in males are discussed.