Case report
Mosaicism for combined tetrasomy of chromosomes 8 and 18 in a dysmorphic child: A result of failed tetraploidy correction?
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* Corresponding author: Gunnar Houge gunnar.houge@helse-bergen.no
1 Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway
2 Department of Clinical Medicine, University of Bergen, Bergan, Norway
3 Department of Pediatrics, Ålesund Hospital, Ålesund, Norway
BMC Medical Genetics 2009, 10:42 doi:10.1186/1471-2350-10-42
Published: 18 May 2009Abstract
Background
Mosaic whole-chromosome tetrasomy has not previously been described as a cause of fetal malformations.
Case presentation
In a markedly dysmorphic child with heart malformations and developmental delay, CGH analysis of newborn blood DNA suggested a 50% dose increase of chromosomes 8 and 18, despite a normal standard karyotype investigation. Subsequent FISH analysis revealed leukocytes with four chromosomes 8 and four chromosomes 18. The child's phenotype had resemblance to both mosaic trisomy 8 and mosaic trisomy 18. The double tetrasomy was caused by mitotic malsegregation of all four chromatids of both chromosome pairs. A possible origin of such an error is incomplete correction of a tetraploid state resulting from failed cytokinesis or mitotic slippage during early embryonic development.
Conclusion
This unique case suggests that embryonic cells may have a mechanism for tetraploidy correction that involves mitotic pairing of homologous chromosomes.