PROXIMAL DELETION OF CHROMOSOME-21 CONFIRMED BY IN-SITU HYBRIDIZATIONAND MOLECULAR STUDIES

Foetal blood sampling was performed at 35 weeks of gestation due to ab normal foetal ultrasound findings. There was apparent monosomy 21 (45, XX,-21) in all mitoses analyzed. The infant died at 37 weeks during de livery. Examination disclosed facial anomalies, clubfeet, hypoplasia o f the left urogenital tract, agenesis of corpus callosum, ventricular dilatation, and heterotopias. Reevaluation of the karyotype showed an unbalanced translocation t(1;21) (q44;q22.11) which resulted from a ma ternal balanced translocation. These findings were confirmed by fluore scence in situ hybridization and molecular studies with chromosome 21 specific markers. The latter showed a proximal deletion of the materna lly derived chromosome 21 including all loci from centromere down to t he D21S210 locus. This case illustrates the need for complementary cyt ogenetic and molecular investigations in cases of apparent monosomy 21 . (C) 1994 Wiley-Liss, Inc.