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| Authors | A Cuschieri E Said S Suleiman |
| Abstract | Introduction: Ring chromosome 21 is a rare abnormality giving rise to a wide variety of phenotypes. The origin of ring 21 chromosome also varies and may include deleted or duplicated material.. Most cases arise de novo, but some are transmitted through generations. We analysed the mechanism of origin of mosaic trisomy 21 that included an additional ring 21 chromosome of maternal origin. Methods: G-banded Karyotype and Telomeric FISH analysis. Results: The baby showed some phenotypic features of Down syndrome. Her karyotype showed a mosaic 46,XX / 47,XX+r21 The ring chromosome was present in the trisomic cell line only, while the 46 XX cell lines all contained a pair of normal chromosome 21. Her mother, a 35 year old lady with a normal phenotype and a record of consistently poor school performance had a non-mosaic karyotype 46,XX -21, + r21. FISH analysis showed the presence of a single centromere, and loss of 21q telomeres in the maternal ring chromosome 21 and in all trisomic cells of the child. Conclusions: The conceptus originated as a maternal non-disjunction giving rise to a trisomy 21 zygote. Mosaicism arose post-zgyotically by trisomic rescue in some blastomeres. Ring chromosome formation involved fusion of the distal ends of the long and short arms of chromosome 21 with consequent loss of 21q telomeres. The telomeric loss apparently had very small effects on the phenotype resulting only in intellectual impairment in the mother. Evidence indicates that ring chromosome 21 also predisposes to non-disjunction. |
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| Journal | Malta Medical Journal |
| Volume | 15 Issue 1-2/suppl. 2003 |
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| Key words | case report, chromosome 21, genetics, phenotype, trisomy, transmission |