In order to determine whether there are particular regions on 22q11 that are prone to rearrangements, the deletion end-points in a large number of VCFS/DGS patients were defined by haplotype analysis.     ///    VCFS/DGS is the most common syndrome associated with 22q11 rearrangements.     ///    "To support this idea further, we identified a family that carries an interstitial duplication of the same 3 Mb region that is deleted in VCFS/DGS patients. "    ///    "Three congenital anomaly disorders, cat-eye syndrome, der() syndrome and velo-cardio-facial syndrome/DiGeorge syndrome (VCFS/DGS) are associated with tetrasomy, trisomy or monosomy, respectively, for part of chromosome 22q11. "    ///    "Most VCFS/DGS patients have a similar 3 Mb deletion, some have a nested distal deletion breakpoint resulting in a 1.5 Mb deletion and a few rare patients have unique deletions or translocations. "    ///    "To investigate this hypothesis, we developed hamster-human somatic hybrid cell lines from VCFS/DGS patients with all three classes of deletions and we now show that the breakpoints occur within similar low copy repeats, termed LCR22s. "