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 (l5q) were found in a girl with developmental delay and mild dysmorpho logical signs. Fluorescence in situ hybridization, using DNA probes of the Prader-Willi/Angelman syndromes (PWS/AS) critical region and chro mosome-15-specific alpha-satellite, combined with molecular analysis u sing dinucleotide repeat polymorphisms within the PWS/AS region and th e parent-of-origin specific methylation sites at the locus D15S63, she d light on how the abnormal karyotype was formed. We suggest that a tr anslocation between the two homologues of maternal chromosomes 15 resu lted in the formation of dup(l5q) and two reciprocal products: an acen tric fragment of 15q that was lost and a centric fragment that underwe nt U-type reunion to form inv dup(15).