Prenatal diagnosis of a mosaic extra structurally abnormal chromosome by spectral karyotyping

A de novo mosaic extra structurally abnormal chromosome (ESAC) was detected in 33 per cent of cultured amniotic fluid cells from a pregnant woman. Nei ther Q-banding nor fluorescence in situ hybridization (FISH) employing a DN A probe for nucleolar organizer region demonstrated the presence of satelli tes on the ESAC. Spectral karyotyping (SKY) was performed in this prenatal case and led to a quick and accurate determination of the ESAC as chromosom e 14 in origin. The SKY finding was confirmed by conventional FISH analysis using a chromosome 14 specific painting probe. Subsequent hybridizations w ith a centromeric probe and a 14q subtelomeric probe were also performed to further characterize the ESAC. Absence of (TTAGGG)n sequence on the ESAC, determined postnatally, suggested it is a ring chromosome 14. Genetic couns elling concerning these findings was provided to the parents who chose to c ontinue the pregnancy. The male infant had no apparent abnormal phenotype a t birth. Copyright (C) 1999 John Wiley & Sons, Ltd.