The occurrence of familial 22q11 deletion syndrome (22q11DS) raises the possibility of prenatal diagnosis for those families at risk, and parents of any new case should be offered deletion screening. Deletion of 22q11 is the most frequent interstitial chromosome deletion observed in man, begging the question as to whether there is any structural predisposition to chromosome rearrangements of this region. The single gene hypothesis predicted that a subset of those velo-cardio-facial syndrome/DiGeorge Syndrome (VCFS/DGS) patients with no apparent deletion of 22q11 would have a small deletion or point mutation inactivating the major gene haploinsufficient in the condition. The frustration at failure to find any loss of function mutations of DGCR genes in patients with no deletion prompted investigators to pursue animal models. Given the cognitive deficits and increased incidence of behavioral difficulty in 22q11DS attempts have been made to identify behavioral correlates in the mouse deletion model.