Simultaneous formation of inv dup(15) and dup(15q) in a girl with developmental delay: origin of the abnormal chromosomes.

Two de novo abnormal derivatives of chromosome 15, inv dup(15) and dup(15q) were found in a girl with developmental delay and mild dysmorphological signs. Fluorescence in situ hybridization, using DNA probes of the Prader-Willi/Angelman syndromes (PWS/AS) critical region and chromosome-15-specific alpha-satellite, combined with molecular analysis using dinucleotide repeat polymorphisms within the PWS/AS region and the parent-of-origin specific methylation sites at the locus D15S63, shed light on how the abnormal karyotype was formed. We suggest that a translocation between the two homologues of maternal chromosomes 15 resulted in the formation of dup(15q) and two reciprocal products: an acentric fragment of 15q that was lost and a centric fragment that underwent U-type reunion to form inv dup(15).