Velocardiofacial (VCFS; 22q11.2; DiGeorge) Syndrome Study

22q11.2 (DiGeorge MIM#188400, Velocardiofacial MIM#192430) syndrome is a hemizygous microdeletion on 22q11.2 of typically 3Mb, encompassing approximately 30 genes and mediated by aberrant homologous recombination and unequal crossing-over events between intrachromosomal flanking low-copy repeats (LCRs). The incidence is 1:4000 live births. While somatic symptoms include congenital cardiovascular and craniofacial abnormalities, recurrent infections and hypocalcemia1 , the most prevalent group of symptoms are neuropsychiatric and include cognitive dysfunction with mild mental retardation, behavioral difficulties and psychosis. The syndrome is associated with a lifetime prevalence of schizophrenia-like illness (phenotypically mostly similar to sporadic schizophrenia) of approximately 25 times that of the general population making the presence of this hemideletion the strongest known risk factor for the development of schizophrenia excepting the presence of a monozygotic twin with the illness. The 22q11 region is implicated in the risk architecture of schizophrenia by several linkage studies and harbors a number of proposed susceptibility genes including genes for Catechol-O-methyltransferase (COMT), proline dehydrogenase (PRODH) and ZDHHC8. The neural basis of these pronounced neurocognitive and psychiatric abnormalities is unknown. The present work proposes to (a) study a group of exceptionally high-functioning, normal intelligence, psychosis-free individuals with 21q11.2 syndrome using a hierarchical multimodal imaging approach to define the intermediate systems level phenotype of the disease combined with deletion mapping techniques and (b) to study the functional effects of single nucleotide polymorphisms in genes in the hemideleted region that have been implicated in schizophrenia, taking advantage of the unique fact that the hemizygous deletion allows immediate construction of molecular haplotypes and of potential epistatic allelic effects. This work is expected to (a) elucidate the pathophysiology of the CNS manifestations of the 22q11.2 syndrome and yield a brain intermediate phenotype that will allow studies in small and atypical deletion individuals in an effort to define individual genes responsible for neurocognitive deficit and increased risk for psychosis, (b) facilitate the identification of functional mechanisms underlying increased risk for schizophrenia for individual susceptibility genes in the deletion and for interacting risk alleles within the deleted locus and (c) prepare the ground for a clinical protocol in which the results from (a) and (b) can be applied to a prospective study evaluating early diagnostic and interventional approaches based on genetic risk and intermediate phenotype ascertainment in this group of patients at high risk for the development of psychosis.