Down syndrome occurs when an individual has a full or partial extra copy of chromosome This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome. A few of the common physical traits of Down syndrome are low muscle tone, small stature, an upward slant to the eyes, and a single deep crease across the center of the palm — although each person with Down syndrome is a unique individual and may possess these characteristics to different degrees, or not at all.
According to the Centers for Disease Control and Prevention, approximately one in every babies in the United States is born with Down syndrome, making Down syndrome the most common chromosomal condition. About 6, babies with Down syndrome are born in the United States each year. For centuries, people with Down syndrome have been alluded to in art, literature and science.
Although other people had previously recognized the characteristics of the syndrome, it was Down who described the condition as a distinct and separate entity. In recent history, advances in medicine and science have enabled researchers to investigate the characteristics of people with Down syndrome. Instead of the usual 46 chromosomes present in each cell, Lejeune observed 47 in the cells of individuals with Down syndrome. It was later determined that an extra partial or whole copy of chromosome 21 results in the characteristics associated with Down syndrome.
In the year , an international team of scientists successfully identified and catalogued each of the approximately genes on chromosome This accomplishment opened the door to great advances in Down syndrome research.
The National Down Syndrome Society envisions a world in which all people with Down syndrome have the opportunity to enhance their quality of life, realize their life aspirations and become valued members of welcoming communities. Your support today helps make this vision a reality.
Thank you! Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate. As the embryo develops, the extra chromosome is replicated in every cell of the body. Mosaicism or mosaic Down syndrome is diagnosed when there is a mixture of two types of cells, some containing the usual 46 chromosomes and some containing Those cells with 47 chromosomes contain an extra chromosome Research has indicated that individuals with mosaic Down syndrome may have fewer characteristics of Down syndrome than those with other types of Down syndrome.
However, broad generalizations are not possible due to the wide range of abilities people with Down syndrome possess. The presence of the extra full or partial chromosome 21 causes the characteristics of Down syndrome. Regardless of the type of Down syndrome a person may have, all people with Down syndrome have an extra, critical portion of chromosome 21 present in all or some of their cells. The cause of the extra full or partial chromosome is still unknown. Maternal age is the only factor that has been linked to an increased chance of having a baby with Down syndrome resulting from nondisjunction or mosaicism.
The additional partial or full copy of the 21st chromosome which causes Down syndrome can originate from either the father or the mother. Down syndrome occurs in people of all races and economic levels, though older women have an increased chance of having a child with Down syndrome. A 35 year old woman has about a one in chance of conceiving a child with Down syndrome, and this chance increases gradually to 1 in by age At age 45 the incidence becomes approximately 1 in The age of the mother does not seem to be linked to the risk of translocation.
Since many couples are postponing parenting until later in life, the incidence of Down syndrome conceptions is expected to increase. Therefore, genetic counseling for parents is becoming increasingly important. This means that Down syndrome occurs in about 1 in every babies. There are three types of Down syndrome.
There are two basic types of tests available to detect Down syndrome during pregnancy: screening tests and diagnostic tests. A screening test can tell a woman and her healthcare provider whether her pregnancy has a lower or higher chance of having Down syndrome.
Screening tests do not provide an absolute diagnosis, but they are safer for the mother and the developing baby.
Diagnostic tests can typically detect whether or not a baby will have Down syndrome, but they can be more risky for the mother and developing baby. Neither screening nor diagnostic tests can predict the full impact of Down syndrome on a baby; no one can predict this.
Extra fluid in this region could indicate a genetic problem. Rarely, screening tests can give an abnormal result even when there is nothing wrong with the baby. Sometimes, the test results are normal and yet they miss a problem that does exist. Diagnostic tests are usually performed after a positive screening test in order to confirm a Down syndrome diagnosis.
Types of diagnostic tests include:. Many people with Down syndrome have the common facial features and no other major birth defects. We explain the condition, its cause, symptoms, and how to diagnose it.
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