MONOZYGOTIC TWINS WITH CHROMOSOME 22Q11 DELETION AND DISCORDANT PHENOTYPE

We report monozygotic twins concordant for 22q11.2 deletion but discor dant for clinical phenotype. Both boys show the typical dysmorphic fea tures with short palpebral fissures, square nasal tip, small mouth, an d both have nasal speech, but only one twin had a heart defect. They s how that the phenotypic variability seen in this microdeletion syndrom e cannot be explained on the basis of genotypic differences alone.