2 SUPERNUMERARY MARKER CHROMOSOMES, DERIVED FROM CHROMOSOME-6 AND CHROMOSOME-9, IN A BOY WITH MILD DEVELOPMENTAL DELAY

We report on a boy with two supernumerary marker chromosomes which wer e identified by fluorescence in situ hybridization and derived from ch romosome 6 and 9. In lymphocytes, a mosaic karyotype was found: 46,XY (17%)/47,XY,r(6) (24%)/47,XY,r(9) (20%)/48,XY,r(6),r(9) (39%). Only mi nor dysmorphic features and mild developmental delay were present. Des pite extensive fluorescence in situ hybridization studies using a larg e panel of probes, we were unable to characterize the marker chromosom es in more detail, mainly because no probes for the chromosome regions involved were available to us. In order to reach a better understandi ng of the clinical relevance of small supernumerary marker chromosomes , it will be necessary to create a widely available set of probes, cov ering all chromosome regions.