Unusual chromosomal mosaicism in Wolf-Hirschhorn syndrome: del(4)(p16)/der(4)(qter-q31.3 :: pter-qter)

We report on the unusual cytogenetic findings in a girl with moderate menta l retardation and a mosaic karyotype 46,XX,deI(4) (p16)/46,XX,der(4)(qter-q 31.3::pter-qter). The facial features observed in the child initially did n ot suggest the diagnosis of Wolf-Hirschhorn syndrome (WHS), but the distinc t facial gestalt became obvious at prepubertal age. Fluorescence in situ hy bridization (FISH) analysis with different probes that map to 4p and 4q hel ped to clarify the karyotype. We discuss the mechanism of appearance of thi s unusual type of mosaicism, which has not been reported before. (C) 2001 W iley-Liss, Inc.