Editor—In a recent issue of this journal, Goodship et al 1 reported monozygotic twins with a deletion in chromosome region 22q11 and a discordant phenotype. They concluded that phenotypic variability in this syndrome cannot be explained on the basis of genotypic differences alone.

Here we report another case of monozygotic twins with an identical deletion in 22q11 but with discordant manifestation of heart disease. The Turkish twins who were born 4 weeks preterm presented with typical symptoms of DiGeorge syndrome. Both boys had characteristic dysmorphic features, including short palpebral fissures, square nasal tip, small mouth, and prominent forehead. Both had hypoplasia of the thymus with markedly decreased levels of CD3 positive lymphocytes (50 and 39% of the total, respectively). Hypocalcaemia owing to low levels of parathyroid hormone (0.76 and 0.7 pmol/l, respectively) was found in both infants, leading to hypocalcaemic seizures in twin 1. Now, at 12 months of age, both infants show significant developmental delay. They are both rather quiet and display a general lack of activity. The second twin's coordination and motor skills …