Towards a genetic definition of velo-cardio-facial syndrome

Abstract

Velo-cardio-facial syndrome (VCFS) is a relatively common genetic disorder, characterized by clefting of the palate, cardiac anomalies, pharyngeal insufficiency and facial dysmorphology. VCFS has been associated with microdeletions on 22q11 leading to hemizygosity of at least 1.5 megabases. I have begun to identify genes in the deleted region and characterize their patterns of expression: this will ultimately permit their evaluation as candidate genes for VCFS. Using an integrated approach to gene isolation and mapping previously developed (Das Gupta et al., 1993), I isolated seven expressed sequence tags (ESTs) representing seven distinct genes from a region of 22q11 that is deleted in a majority of VCFS patients. I also mapped a previously cloned gene, gamma glutamyl transferase (GGT), to this region. This approach uses hybridization selection to isolate YAC-specific cDNA minilibraries; the cDNAs are then used to fragment the YAC by homologous recombination to ascertain their relative order and determine the physical distance between them. The eight ESTs have been used to build a high resolution contig for {dollar}-{dollar}350 kb of 22q11. One of the ESTs isolated from the YAC was a previously cloned but unmapped gene, GGT-Rel, while the other six ESTs represent novel genes. The expression of these genes has been analyzed by RT-PCR and/or Northern blot analysis. Longer cDNAs have been isolated and sequenced for 3 of the 6 novel ESTs. I have identified 3 gene families that are repeated on chr. 22 (and on other chromosomes), as well as three single copy genes. One of these novel ESTs (AM85-40) is a member of the immunoglobulin super family. The exact order of these genes with respect to each other, as well as to the breakpoint of the deletion in the patients, has been established through chromosome fragmentation.