Well before the genetic link to Down syndrome was discovered, John Lagdon Down described it in 1866 as a distinct set of characteristics. He distinguished Down syndrome from other conditions by noting some of the common features associated with it, such as thin, straight hair, a small nose, and a broad face. Down is also credited with naming the condition “mongolism.” It was called this because most infants with this condition have a somewhat Oriental appearance. This term is no longer used and we refer to this

There are three major types of Down syndrome. The first and most common type is called Nondisjunction Trisomy 21. This type occurs in about 95% of the babies born with Down syndrome. This type of Down syndrome probably results from some genetic material sticking together or failing to disjoin during development of the egg or sperm or during fertilization. The second type is called Translocation Trisomy 21. This type occurs when the extra 21 chromosome breaks off during cell division and attaches to another chromosome. This is the only type of Down syndrome that can result from a condition in the parent’s genes. Two to three percent of children with Down syndrome have this type. The third and least common form of Down syndrome is known as Mosaicism. This type occurs in only one to two percent of all people with Down syndrome. In Mosaicism, a faulty cell division occurs in one of the early cell divisions after fertilization. As in Nondisjunction Trisomy 21, something causes the cells to divide unevenly. But when this occurs in the second or third cell division, only some of the cells contain the extra chromosome. The percentage of cells affected differs from child to child.

condition as simply Down syndrome. By the early 1930s, some researchers began to suspect that Down syndrome might be caused by a chromosomal abnormality. In 1959, Jerome Lejune discovered that cells grown from individuals with Down syndrome had an extra chromosome. Later the exact location of the extra chromosome was found to be at the number 21 chromosome.

Some other factors that are important to note about children with Down syndrome are that they are more similar to the average child in the community than they are different. Children with Down syndrome look more like their families then they do one another. They have a full complement of emotions and attitudes, are creative and imaginative in play, and grow up to live independent lives with varying degrees of support and accommodations needed.

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