The 22q11.2 deletion syndrome.

The 22q11.2 deletion syndrome (22q11DS) encompasses DiGeorge syndrome, velo-cardio-facial syndrome and conotruncal anomaly face syndrome and is due to a microdeletion of chromosome 22q11.2. This is the most frequent known interstitial deletion found in human with an incidence of 1 in 4,000 live births. A large number of clinical findings have been reported in affected patients, including cardiac defects, characteristic facial features, thymic hypoplasia, cleft palate, hypoparathyroidism, learning difficulties and psychiatric disorders. A comprehensive evaluation and follow-up program is necessary for patients with 22q11DS. A striking aspect of the 22q11DS phenotype is its variability, the basis of which remains unclear, and no phenotype-genotype correlation has been made. The structures primarily affected in patients with 22q11DS are derivatives of the embryonic pharyngeal arches and pouches suggesting that haploinsufficiency of the gene(s) on the deleted region, spanning 2-3 Mb, is important in pharyngeal arch/pouch development. Extensive gene searches have been successful in identifying more than 30 genes in the deleted segment. Although standard positional cloning has failed to demonstrate a role for any of these genes in the syndrome, the use of experimental animal models and advanced genome manipulation technologies in mice have been providing an insight into the developmental role of some of these genes, including TBXI. In this review, the clinical features and management of patients with 22q11DS are integrated with our current understanding of the embryological and molecular basis of this syndrome, as presented at the 1235th Meeting of The Keio Medical Society.