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Clin Genet. 1993 Jul;44(1):26-31.

Ring chromosome 20 with loss of telomeric sequences detected by multicolour PRINS.

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  • 1Institute of Human Genetics, University of Aarhus, Denmark.


A ring chromosome 20 in a male infant with epileptic seizures, mental and somatic growth retardation, and behavioural disturbances is described. Conventional cytogenetics revealed the karyotype to be 46,XY,r(20)(pter-->qter) and no signs of mosaicism were found. Fluorescence in situ hybridisation using the clone p20Z1 identified the ring to be derived from chromosome 20. By counting 111 metaphases, only 7% were found to be missing the ring. The absence of telomeric sequences in the ring chromosome was demonstrated by multicolour PRINS: a three-step PRimed IN Situ labelling technique, using unlabelled primers. A terminal deletion of both arms thus seems to be the cause of the ring formation in the proband. Bivariate flow-analysis of chromosomes verified a deletion of the ring chromosome. The clinical and cytogenetic findings are compared with previous cases. A specific ring 20 syndrome seems justified.

[PubMed - indexed for MEDLINE]
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