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 weeks' gestation) referred for karyotype analysis following the observation of a short femur at the ultrasound scan. Analysis of 12 Y-chromosome loci by fluorescent in situ hybridization (FISH) and polymerase chain reaction (PCR) demonstrated that the marker chromosome is of Y origin 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 close to the centromere. The present report illustrates the importance of FISH and PCR techniques as a complement to cytogenetic methods for accurate identification and characterization of chromosome rearrangements in prenatal diagnosis.