Preferential involvement of the short arm in chromosome 8-derived supernumerary markers and ring as identified by chromosome arm painting

We report on the use of fluorescence in situ hybridization (FISH) with spec ific chromosome 8 arm painting to characterize further small supernumerary chromosome 8-derived markers/rings (SMC/SRC) identified in three patients. Two patients (patients 1 and 2) who carried the marker (SMC) were evaluated because of mental retardation and minor facial anomalies. The patient (pat ient 3) who carried the ring (SRC) had ventriculomegaly. Parental blood chr omosomes of patients 2 and 3 were normal and unavailable on patient 1. The identification of the SMC/SRC was first characterized by FISH specific alph a-repeat centromeric probes, second by FISH whole chromosome painting (WCP) , and finally by FISH chromosome arm painting (CAP). The latter showed invo lvement of only the short arm of chromosome 8 in all three SMC/SRC cases, s uggesting a U-type exchange mechanism. (C) 2000 Wiley-Liss, Inc.