Phenotypic discordance in monozygotic twins with 22q11.2 deletion

Am J Med Genet. 1998 Jul 24;78(4):319-21.


We report on male monozygotic twins with 22q11.2 deletion and discordant phenotypes. The twins had twin-to-twin transfusion syndrome. Twin 1, the smaller of the pair, had Tetralogy of Fallot, a characteristic facial appearance, swallowing dysfunction, anal atresia, short stature, and mental retardation, whereas twin 2 had a characteristic facial appearance but no other signs of the 22q11 deletion syndrome. Fluorescence in situ hybridization analysis showed a microdeletion on chromosome 22q11.2 in both twins. Zygosity analysis gave a probability of monozygosity greater than 99.999%. These observations indicate that environmental factors or postzygotic events play a role in the phenotypic variability in the twins.

Publication types

  • Case Reports

MeSH terms

  • Abnormalities, Multiple / genetics*
  • Body Constitution
  • Child
  • Chromosome Deletion*
  • Chromosomes, Human, Pair 22*
  • DiGeorge Syndrome / genetics
  • Diseases in Twins / genetics*
  • Face / abnormalities
  • Female
  • Fetofetal Transfusion
  • Humans
  • In Situ Hybridization, Fluorescence
  • Intellectual Disability / genetics
  • Karyotyping
  • Male
  • Phenotype
  • Pregnancy
  • Tetralogy of Fallot / genetics
  • Twins, Monozygotic*