Delimitation of duplicated segments and identification of their parental origin in two partial chromosome 3p duplications

Two chromosome 3 short arm duplications identified through G-banding were further investigated using fluorescence in situ hybridization (FISH) and polymerase chain reaction (PCR) of microsatellite markers, aiming at mapping breakpoints and disclosing mechanisms of origin of these chromosome aberrations. Patient 1 was found to be a mosaic: a 3p12, 3p21 duplication was observed in most of his cells, and a normal cell line occurred with a frequency of about 3% in blood. In situ hybridization of chromosome 3 short- and long-arm libraries confirmed the short-arm duplication. Using FISH of short-arm sequences, the YAC 961_h_3 was shown to contain the proximal breakpoint (3p12.1 or 3p12.2), and the distal breakpoint was located between the YACs 729 c 3 and. 806_h_2, which are adjacent in the WC 3.10 contig (3p21.1). In Patient 2, G-banding indicated a 3p21 --> 3p24 duplication, without mosaicism. In situ hybridization of chromosome 3 short- and long-arm libraries confirmed the duplication of short-arm sequences. FISH of chromosome 3 sequences showed that the YAC 749 a 7 spanned the proximal breakpoint (3p21.33). The distal breakpoint mapped to the interval between YACs 932_b_6 (3p24.3) and 909_b_6 (3p25). In both cases, microsatellite genotyping pointed to a rearrangement between paternal sister chromatids. (C) 2002 Wiley-Liss, Inc.