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Confined placental mosaicism (CPM) represents a discrepancy between the chromosomal makeup of the cells in the placenta and the cells in the baby. CPM was first described by Kalousek and Dill in 1983. CPM is diagnosed when some trisomic cells are detected on chorionic villus sampling and only normal cells are found on a subsequent prenatal test, such as amniocentesis or fetal blood sampling. In theory, CPM is when the trisomic cells are found only in the placenta. CPM is detected in approximately 1-2% of ongoing pregnancies that are studied by chorionic villus sampling (CVS) at 10 to 12 weeks of pregnancy. Chorionic villus sampling is a prenatal procedure which involves a placental biopsy. Most commonly when CPM is found it represents a trisomic cell line in the placenta and a normal diploid chromosome complement in the baby. However, the fetus is involved in about 10% of cases. ==Pathogenesis== CPM occurs in one of two ways: *''Mitotic CPM'' - Mitotic non-disjunction can occur in a trophoblast cell or a non-fetal cell from the inner cell mass creating a trisomic cell line in the tissue which is destined to become the placental mesoderm. *''Meiotic CPM'' - Alternatively, CPM can occur through the mechanism of ''trisomic rescue''. If a trisomic conception undergoes trisomic rescue in certain cells, including those that are destined to become the baby, then the remaining trisomy cells may be confined to the placenta. Several factors influence the pattern of normal and abnormal cells in the developing embryo. Reduced or improved replication rates of the trisomic cells could affect the number of abnormal cells compared to the number of normal cells. The abnormal cells may fail to differentiate or function properly and could be lost. It is also possible that there is no selection against the abnormal cells, but their presence could compromise the pregnancy on a whole. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Confined placental mosaicism」の詳細全文を読む スポンサード リンク
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