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Named for endocrinologist Angelo DiGeorge, who first described the syndrome in 1965, the 22q11 microdeletion associated with DGS is believed to occur about once in 4000 to 5000 births. Children born with chromosome 22-deletion disorders share several characteristics, including cardiac defects, abnormal facies, thymic hypoplasia, cleft palate, and hypocalcemia. Region 22q11.2 deletions may be implicated in a significant proportion of newborns with heart defects. Although patients have many different deletion endpoints, researchers found that most have a 1.5-Mb deletion [the DiGeorge chromosomal region (DGCR)]. Deletion size has not been correlated with disorder severity. To identify candidate genes spanning the minimal region critical to DGS development, researchers studied a rare DGS individual with a balanced translocation between chromosomes 2 and 22. Gene transcripts were identified by direct screening of cDNA libraries, exon amplification, cDNA selection, and GRAIL sequence analysis. Attention is now focused on two genes located directly at the breakpoint; one of these codes for a protein that resembles the androgen receptor, suggesting a possible role in developmental regulation. A complete cosmid contig of DGCR has been constructed and is now being sequenced in collaboration with Bruce Roe (University of Oklahoma). |
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