Molecular genetic analysis of the DiGeorge syndrome among Korean patients with congenital heart disease.

The DiGeorge syndrome (DGS) is a developmental defect of the third and fourth pharyngeal pouches, which is associated with congenital heart defects, hypoparathyroidism, cell-mediated immunodeficiency, velo-pharyngeal insufficiency and craniofacial dysmorphism. The aetiological factor in a great majority of DGS cases is monosomy for the chromosomal region 22q11. To analyze DGS at the molecular level, a new molecular probe (DGCR680) encompassing the ADU balanced translocation breakpoint was prepared. When 13 Korean patients with DGS-type congenital heart disease were analyzed with this probe, 9 turned out to have a deletion at this locus, and all of them except one exhibited a typical facial dysmorphism associated DGS. Though only 9 independent patients were detected to have a deletion at the locus using the commercial probe N25 (D22S75), which maps at about 160 kb from the ADU breakpoint to the telomeric end, results from fluorescence in situ hybridization revealed a deletion in all cases tested at this locus. Two patients who had a deletion at the locus D22S75 but not at DGCR680 did not exhibit any DGS-type facial abnormalities. This result implies that the 680 bp probe covering the ADU translocation breakpoint might be a candidate for a molecular marker that can distinguish a specific phenotype, such as facial features associated with the DiGeorge syndrome. This study also suggested that systematic approaches with several small DNA probes along the DGCR could help to dissect the complex phenotypes associated with the DiGeorge syndrome, such as cardiac defects, abnormal faces, thymic hypoplasia, cleft palate, and hypocalcemia, etc.