Origin of a prenatal mosaic supernumerary neocentromeric derivative chromosome 13 determined by QF-PCR.

Neocentromeres are mitotically stable human derivative centromeres without alpha-satellite DNA which are able to provide stability to rearranged chromosome fragments that would otherwise be acentric and rapidly lost. A female fetus was found to be mosaic for a supernumerary marker chromosome: 47,XX,+mar[3]/46,XX[36]. The marker was identified by fluorescence in situ hybridization and G-band as an inversion duplication of 13q21→13qter, with a neocentromere present at 13q21, in approximately 9% of colonies examined. Parental blood karyotypes were normal. QF-PCR performed on blood samples from both parents and the second amniotic fluid sample showed evidence of a second maternal allele at markers D13S258 (13q21) and D13S628 (13q31-q32), indicating formation at maternal meiosis I/II. This is the first reported case where the detection and origin of a low-level mosaic prenatal neo(13) were confirmed by QF-PCR.

Interstitial deletion of chromosome 2p16.2p21.

We report on a female who presents with an atrial septal defect (ASD), mild hypotelorism, a prominent nasal bridge, a long smooth philtrum, mild developmental delay and a de novo interstitial deletion of the short arm of chromosome 2p, del (2)(p16.2p21). This is the first report of a deletion in chromosome 2 involving those particular breakpoints. We propose that this may represent a new recognizable chromosomal phenotype.