PRENATAL IDENTIFICATION OF AN ISOCHROMOSOME FOR THE SHORT ARM OF THE Y I(YP), BY CYTOGENETIC AND MOLECULAR ANALYSES

A case of 45,X/46,X,+mar mosaicism was detected in a male fetus (27 we eks' gestation) referred for karyotype analysis following the observat ion of a short femur at the ultrasound scan. Analysis of 12 Y-chromoso me loci by fluorescent in situ hybridization (FISH) and polymerase cha in reaction (PCR) demonstrated that the marker chromosome is of Y orig in and corresponds to an authentic isochromosome for the short arm of the Y chromosome, i(Yp). The breakpoint on this marker is in YQ11.1 cl ose to the centromere. The present report illustrates the importance o f FISH and PCR techniques as a complement to cytogenetic methods for a ccurate identification and characterization of chromosome rearrangemen ts in prenatal diagnosis.