GENETIC-COUNSELING IN A PRENATAL MARKER CHROMOSOME IDENTIFIED AS AN I(18P) BY IN-SITU HYBRIDIZATION

The origin of a de novo metacentric small marker chromosome found in a cytogenetic study in amniotic fluid was determined by fluorescence in situ hybridization (FISH) using chromosome specific probes. It was id entified as an isochromosome 18p. We want to emphasize that when an ex tra chromosome is found in prenatal diagnosis and it cannot be identif ied by conventional cytogenetics banding, FISH should be applied in or der to give real risks for fetal anomalies and an accurate genetic cou nselling.