A MOLECULAR ANATOMICAL ANALYSIS OF MOSAIC TRISOMY-16

A one-month-old child presenting with an aortic coarctation was found to have a left single transverse palmar crease and proportionate growt h delay on physical examination, prompting a peripheral blood chromoso me analysis. This showed a mosaic trisomy of chromosome 16, subsequent ly observed to decrease with the passage of time. As her phenotype was relatively benign, further analysis was performed to define more prec isely the extent of her mosaicism given the supposedly lethal nature o f the aneuploid cell line. Fluorescence in situ hybridisation and CA r epeat polymorphism studies demonstrated the aneuploidy in multiple tis sues, including the structurally affected aorta. Molecular analysis sh owed both maternal chromosomes 16 to be present in the trisomic cells, but maternal heterodisomy was not present in the diploid cells. Given the increasing number of individuals described with aneuploid mosaici sm, we suggest that the study of multiple tissues is a necessary appro ach, the eventual goal being the appreciation of the relationship betw een the characteristics of a somatic mosaicism and the phenotype it im parts.