DE-NOVO APPARENTLY BALANCED COMPLEX CHROMOSOME REARRANGEMENT (CCR) INVOLVING CHROMOSOME-4, CHROMOSOME-18, AND CHROMOSOME-21 IN A GIRL WITH MENTAL-RETARDATION - REPORT AND REVIEW

We describe a complex and unique, de novo apparently balanced transloc ation involving chromosomes 4, 18, and 21 with 4 breakpoints, in a pat ient who was referred for an evaluation of possible fragile-X syndrome . Fluorescence in situ hybridization (FISH) confirmed the complexity o f the rearrangement and showed the derivative 21 to be composed of 3 d istinct segments derived from chromosomes 21, 18, and 4, The derivativ e chromosome 18 had undergone a double translocation, the first such e vent to be described in constitutional complex chromosomal rearrangeme nts (CCRs) involving chromosome 18, A review of these CCRs suggests th e existence of a breakpoint ''hot spot'' on 18q21. (C) 1998 Wiley-Liss , Inc.