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Resource Description: 
WXXI, Second Opinion's producing station, has compiled a list of stories, resources and media related to developmental disabilities, with the goal of helping people and communities become more inclusive.
The National Down Syndrome Society is an American organization that offers support to people with Down syndrome, their families, friends, teachers, and coworkers, and educates the general public about Down syndrome.
The National Association for Down Syndrome supports all persons with Down syndrome in achieving their full potential.
The Global Down Syndrome Foundation is dedicated to significantly improving the lives of people with Down syndrome through Research, Medical Care, Education and Advocacy.
Episode number: 
1305

Life expectancy for people with Down Syndrome has increased over the last 30 years – from 25 years old in 1983 to 60 years old today.  While Down Syndrome carries certain health issues and risks, people with Down Syndrome and their families are moving beyond the limitations of this disability. Patient and Special Olympic medalist Frankie Antonelli and his mother Debbie share what their family has done to help Frankie reach his full potential.

[Source: National Down Syndrome Society]

 

What is Down Syndrome?

In every cell in the human body there is a nucleus, where genetic material is stored in genes.  Genes carry the codes responsible for all of our inherited traits and are grouped along rod-like structures called chromosomes.  Typically, the nucleus of each cell contains 23 pairs of chromosomes, half of which are inherited from each parent. Down syndrome occurs when an individual has a full or partial extra copy of chromosome 21.

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.

How Common is Down Syndrome?

One in every 691 babies in the United States is born with Down syndrome, making Down syndrome the most common genetic condition. Approximately 400,000 Americans have Down syndrome and about 6,000 babies with Down syndrome are born in the United States each year. 

There are three types of Down syndrome:  trisomy 21 (nondisjunction), translocation and mosaicism.

Trisomy 21 (Nondisjunction)

Down syndrome is usually caused by an error in cell division called "nondisjunction."  Nondisjunction results in an embryo with three copies of chromosome 21 instead of the usual two.  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.  This type of Down syndrome, which accounts for 95% of cases, is called trisomy 21. 

Mosaicism 

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 47.  Those cells with 47 chromosomes contain an extra chromosome 21. 

Mosaicism is the least common form of Down syndrome and accounts for only about 1% of all cases of Down syndrome.  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. 

Tanslocation 

In translocation, which accounts for about 4% of cases of Down syndrome, the total number of chromosomes in the cells remains 46; however, an additional full or partial copy of chromosome 21 attaches to another chromosome, usually chromosome 14. The presence of the extra full or partial chromosome 21 causes the characteristics of Down syndrome.

What Causes 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.  This additional genetic material alters the course of development and causes the characteristics associated with Down syndrome.  

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.  However, due to higher birth rates in younger women, 80% of children with Down syndrome are born to women under 35 years of age. 

There is no definitive scientific research that indicates that Down syndrome is caused by environmental factors or the parents' activities before or during pregnancy. 

The additional partial or full copy of the 21st chromosome which causes Down syndrome can originate from either the father or the mother. Approximately 5% of the cases have been traced to the father.

 

Medline Plus

Medline Description: 

Conduct an off-site search for Down syndrome from MedlinePlus.  These up-to-date search results are based on search terms specific to Second Opinion Key Points.

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