Hemizygosity for a region of chromosome 22q11 causes a wide range of congenital defects including Digeorge syndrome, Shprintzen (velo-cardiofacial syndrome) and congenital heart disease. There are now several well characterised DNA probes that can detect these deletions, and the saturation cloning of the region is proceeding. The aim of this proposal is to conduct a multi-center analysis of this group of birth defects. The project has several goals. We wish to determine the range of birth defect and phenotypic variability associated with deletions of chromosome 22q11. With specific abnormalities, such as congenital heart defects, we will estimate the proportion of cases in which hemizygosity within 22q11 is causative. On the basis of our current data we predict that congenital heart defect will be the major cause of morbidity and mortality secondary to this chromosome abnormality. These experiments will allow us to refine our shortest region of overlap map for the genes which have a haploinsufficient phenotype, and detect any correlation between size/position of deletion and resulting phenotype. This will facilitate efforts to isolate candidate cDNAs. The deletion screening experiments will identify those patients with no apparent chromosome 22 abnormality who would be candidates for having intragenic mutations. Appropriate candidate genes will be screened for such mutations. Subsiduary goals include comparative mapping between mouse and man, and mapping of chromosome deletion breakpoints.
The main experimental tasks will be the identification of patients and their deletion analysis using fluoresence in situ hybridization and quantitative Southern hybridization. The consortium established to conduct this programme consists of groups with an established interest and experience in chromosome 22q11 haploinsufficiencies or in mutation screening. The laboratories involved have a strong tradition of collaboration having already Worked together on Digeorge syndrome and/or cystic fibrosis.
Funding SchemeCSC - Cost-sharing contracts
3000 DR Rotterdam
NE2 4AA Newcastle - Upon Tyne