What is the likelihood of having a second child with Down syndrome? However, in about one-third of cases, one parent is a carrier of a translocated chromosome. Most cases are sporadic – chance – events. The age of the mother does not seem to be linked to the risk of translocation. However, in one-third of cases of Down syndrome resulting from translocation, there is a hereditary component – accounting for about 1% of all cases of Down syndrome (Facts about Down syndrome, 2021). Heredity is not a factor in trisomy 21 (nondisjunction) and mosaicism. This accomplishment opened the door to great advances in Down syndrome research.Īll 3 types of Down syndrome are genetic conditions (relating to the genes), but only 1% of all cases of Down syndrome have a hereditary component (passed from parent to child through the genes). In the year 2000, an international team of scientists successfully identified and catalogued each of the approximately 329 genes on chromosome 21. It was later determined that an extra partial or whole copy of chromosome 21 results in the characteristics associated with Down syndrome. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome. In 1959, the French physician Jérôme Lejeune identified Down syndrome as a chromosomal condition. In recent history, advances in medicine and science have enabled researchers to investigate the characteristics of people with Down syndrome. Although other people had previously recognized the characteristics of the syndrome, it was Down who described the condition as a distinct and separate entity. It was this scholarly work, published in 1866, that earned Down the recognition as the “father” of the syndrome.
It wasn’t until the late nineteenth century, however, that John Langdon Down, an English physician, published an accurate description of a person with Down syndrome. For centuries, people with Down syndrome have been alluded to in art, literature, and science.
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