Congenital cardiac defect in a patient with mosaic 45,X/46,XX,i(21q) karyotype.

A baby is described with 45,X/46,XX,i(21q) mosaicism. DNA analysis indicated that the abnormality arose from two independent postzygotic mutations in a 46,XX zygote, involving the paternal chromosomes 21 and X. In agreement with previous reports, most of the clinical dysmorphisms observed were consistent with Down syndrome. Moreover, congenital heart disease consisted of an atrioventricular canal associated with slight hypoplasia of the left ventricle and a mitral anulus, a complex defect including features found in both Down and Turner syndromes.