Concordance of congenital heart defects in two pairs of monozygotic twins: pulmonary stenosis and tetralogy of Fallot.

Two pairs of twins with specific concordance in congenital heart lesions are presented. We reviewed all the monozygotic twins with specific concordance in congenital heart lesions in the last 18 years. Two pairs were found. First, a pair of 13 years-old monozygotic female twins; a severe infundibular and pulmonary valve stenosis was discovered in both girls. In the second pair of twins (8 years-old boys), Tetralogy of Fallot was diagnosed by echocardiogram, cardiac catheterization and angicardiography. In fluorescence hybridization test in situ all patients were negative for microdeletion in chromosome 22q11. Anatomic differences between twins are not enough explained on genetic bases; it's necessary to consider the role of other factors, probably acquired during the first stages of embryonic development. These are the two first pairs of twins with specific concordance in congenital cardiac lesions reported in Mexico.