Molecular Definition of22q11Deletions in151Velo-Cardio-Facial Syndrome Patients

Summary Velo-cardio-facial syndrome (VCFS) isarelatively common developmental disorder characterized bycraniofacial anomalies andconotruncal heart defects. ManyVCFSpatients have hemizygous deletions forapart of22q11, suggesting that haploinsufficiency inthis region isresponsible forits etiology. Because mostcases ofVCFSaresporadic, portions of22q11 maybeprone torearrangement. Tounderstand themolecular basis forchromosomal deletions, wedefined theextent ofthedeletion, bygenotyping 151VCFSpatients andperforming haplotype analysis on105, using 15consecutive polymorphic markers in22q11. Wefound that 83% hadadeletion and>90%ofthese hadasimilar -3Mb deletion, suggesting that sequences flanking thecommon breakpoints aresusceptible torearrangement. Wefound no correlation between thepresence orsize ofthedeletion and thephenotype. To further define thechromosomal breakpoints amongtheVCFSpatients, wedeveloped somatic hybrid cell lines from aset ofVCFSpatients. An11-kb resolution physical mapofa1,080-kb region that includes deletion breakpoints wasconstructed, incorporating genes andexpressed sequence tags (ESTs) isolated bythehybridization selection method. Theordered markers wereused toexamine thetwoseparated copies ofchromosome 22in thesomatic hybrid cell lines. Insomecases, wewereable tomapthechromosome breakpoints within asingle cosmid. A 480-kb critical region forVCFShasbeendelineated, including thegenes forGSCL,CTP,CLTD,HIRA,and TMVCF,aswell asanumber ofnovel ordered ESTs.