How is the majority of cases of Edward's Syndrome classified?

The majority of cases of Edward's Syndrome, also known as Trisomy 18, are classified as complete trisomy. This means that there are three copies of chromosome 18 present in every cell of the body instead of the usual two. Such complete trisomy typically arises due to nondisjunction during meiosis, which is the failure of homologous chromosomes to separate properly during cell division. As a result, the affected individual receives an extra chromosome 18 from either the mother or the father.

This complete extra chromosome 18 leads to the developmental and physical challenges associated with Edward's Syndrome, including severe cognitive impairment and multiple congenital anomalies. The very nature of complete trisomy means that the entire set of cells in the body is affected, contributing to the characteristic clinical features of the condition.

In contrast, although partial trisomies, translocations, and mosaicism can also involve extra genetic material from chromosome 18, they do not represent the most common form of Edward's Syndrome. Partial trisomy would imply that only a segment of chromosome 18 is duplicated. Translocations involve a segment of one chromosome being transferred to another chromosome and would not lead to the clinical presentation typical of Edward's Syndrome as seen with complete trisomy. Mosaicism,