G-banded chromosome analysis: Valuable resource as illustrated by a prenatal case of mosaic tetrasomy 9P.

9p tetrasomy is a rare chromosomal imbalance defined by the presence of a supernumerary isochromosome involving the short arm of chromosome 9, or isodicentric chromosome that additionally includes 9q material. Prenatal diagnosis of mosaic or non-mosaic tetrasomy 9p is uncommon. Here we present a prenatal case of mosaic tetrasomy 9p in a fetus with multiple abnormalities using CGH microarray where conventional karyotyping assisted in elucidating the nature of the imbalance. While microarray provides a significant advantage in terms of resolution, it has limited capacity to ascertain the cytogenetic mechanism of copy number changes identified.