Molecular cytogenetic study of supernumerary marker chromosomes in an unselected group children

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Abstract
We report on an unselected group of 24 children with small supernumerary marker i chromosomes, found in a large sample of 34,910 consecutive newborns karyotyped at I birth. Sixteen of these were available for re‐examination. With the use of in situ hybridization with a‐satellite centromere probes and satellite III, ribosomal and (3‐satellite DNA probes, we have characterized these markers. In 14 of the 16 cases we have been able to determine the chromosomal origin of the marker. Twelve of the markers are derived from the acrocentric chromosomes. Of these 12 markers, 4 are derived from chromosome 14, 4 from chromosome 22, 3 from I chromosome 15 and one is from either chromosome 13 or 21. Ten of these markers were j initially ascertained with the satellite III DNA probe, taking advantage of the fact 1 that satellite III DNA is found in the cen‐I tromeric region of the following chromo‐J somes: 1, 5, 9, 13, 14, 15, 16, 20, 21, 22, and Y. I Two markers were derived from chromo‐) somes 4 and 8. The origin of the last 2 mark‐i ers could not be determined with the techniques employed. Only one of these children is psychometrically retarded and has a pe culiar appearance. Unfortunately we were; not able to determine the origin of the I marker in her case. All other children developed normally.