Pathology of Multiple Pregnancy

pp 169-197

Anomalous Development of Twins

  • Virginia J. BaldwinAffiliated withDepartment of Pathology, British Columbia’s Children’s Hospital

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As we learn more about the human genome and develop more sophisticated ways of studying diseases, disorders, and disturbed development, the borders between these abnormalities become harder to define. For example, as we learn more about the underlying biochemical defects in dwarfing syndromes such as thanatophoric dysplasia, this “malformation” becomes more like an inborn error of metabolism—a genetic defect or alteration with a specifically altered or absent product, leading to a predictable set of consequences depending on the role of that product. Considering this concept, it is perhaps somewhat artificial to discuss developmental/morphologic/structural anomalies separate from the sorts of diseases and disorders reviewed in Chapter 6. However, we are still a long way from defining the underlying molecular mechanisms in most structural variations from “normal,” so there is probably more we can learn from reviewing them in a broader context. Careful analysis of patterns of malformations and associated epidemiologic characteristics may help define where the basic defect could be looked for, and examinations of malformations in twins may provide particularly useful data.