Mosaicism for combined tetrasomy of chromosomes 8 and 18 in a dysmorphic child: a result of failed tetraploidy correction?
BACKGROUND
Mosaic whole-chromosome tetrasomy has not previously been described as a cause of fetal malformations.


METHODS
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.


CONCLUSIONS
This unique case suggests that embryonic cells may have a mechanism for tetraploidy correction that involves mitotic pairing of homologous chromosomes.
Houge
Gunnar
G
Center for Medical Genetics and Molecular Medicine, Haukeland University Hospital, Bergen, Norway. gunnar.houge@helse-bergen.no
Lybaek
Helle
H
Gulati
Sasha
S
D000015:Abnormalities, Multiple / Q000235:genetics*; D000483:Alleles; D000782:Aneuploidy; D002887:Chromosomes, Human, Pair 18; D002898:Chromosomes, Human, Pair 8; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D007223:Infant; D009030:Mosaicism; D009630:Nondisjunction, Genetic; D010641:Phenotype; D020080:Tandem Repeat Sequences