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Three chromosomes and a baby : cytogenetic, biological, and clinical aspects of the trisomic placenta Yong, Paul John

Abstract

Trisomy--the presence of an extra chromosome--is found in one in four miscarriages, while 0.5-1% of ongoing pregnancies assessed by chorionic villus sampling have trisomy mosaicism with the abnormality predominantly or completely confined to the placenta (’confined placental mosaicism’ (CPM)). Trisomy of chromosome 16, in particular, may be the most common chromosome abnormality at conception. In this thesis, ongoing trisomy CPM pregnancies, especially those involving trisomy 16, were first investigated to clarify the distribution of maternal-fetal [i.e. foetal] and pediatric [i.e. paediatric] outcomes and to delineate the predictors of poorer outcome. CPM of trisomy 16 (CPM 16) was found to be associated with fetal growth restriction and malformation, as well as maternal preeclampsia, although long-term growth and development of the newborns was reassuring. The presence of amniotic fluid trisomy and uniparental disomy (UPD) increased risk of poorer outcome in CPM16 pregnancies. Also, the level of trisomy in the trophoblast, for both CPM16 and other trisomy CPM, was the key placental lineage important for pregnancy outcome. Second, trisomic spontaneous abortions, especially trisomy 16 miscarriages, were studied to identify biological mechanisms in the pathogenesis of the trisomic placenta, such as trophoblast outgrowth and fibroblast protein kinase expression. Although trisomic trophoblast outgrowth was variable, and apparently normal in trisomy 15, there was a defect in outgrowth in trisomy 16 trophoblast. As well, protein kinase profiling of trisomy 16 fibroblasts showed both dosage-effects and amplified instability when compared to euploid fibroblasts. In conclusion, the trisomic placenta can have significant and varied effects on biological function and the clinical outcome of mother, fetus [i.e. foetus], and newborn.

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