Monozygotic twins concordant for blood karyotype, but phenotypically discordant: a case of "mosaic chimerism".
We report on 23 years old discordant monozygotic (MZ) twins, one with minor anomalies and mental delay, the other one being normal. Both had 46,XX,dup(11)(p12p15)/46,XX mosaicism in blood, with a similar proportion of abnormal cells (respectively, 16% and 17%). However, interphase fluorescence in situ hybridization (FISH) analysis performed on buccal smear and urinary sediment using specific probes located at the duplicated region showed that mosaicism was only present in the abnormal twin, with 68% abnormal cells. We hypothesize that the postzygotic chromosomal rearrangement may have occurred early in one embryo after the twinning event, and the blood mosaicism observed in both twins would have resulted from blood exchanges via placental anastomoses. This hypothesis of chimerism is strongly supported by twin-to-twin transfusion syndrome observed during fetal life of our twins. This case and those previously reported lead us to suggest that blood is particularly unsuitable for cytogenetic investigations of twins.
Bourthoumieu
Sylvie
S
Department of Histology, Limoges University Hospital, Limoges, France.
Yardin
Catherine
C
Terro
Faraj
F
Gilbert
Brigitte
B
Laroche
Cécile
C
Saura
Robert
R
Vincent
Marie-Claire
MC
Esclaire
Françoise
F
D000328:Adult; D002869:Chromosome Aberrations; D002871:Chromosome Banding; D002880:Chromosomes, Human, Pair 11 / Q000235:genetics; D004200:Diseases in Twins / Q000235:genetics / Q000473:pathology; D005260:Female; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D008607:Intellectual Disability / Q000473:pathology; D007621:Karyotyping; D009030:Mosaicism; D010641:Phenotype; D014430:Twins, Monozygotic / Q000097:blood / Q000235:genetics*