The ADRC of Dane County provides information about resources and support on all aspects of life related to aging or living with a disability and is a one-stop shop for older adults, people with disabilities and their families. ADRC staff are unbiased and knowledgeable professionals who listen to your concerns, help clarify your options and direct you to appropriate resources. The ADRC is also the access point for information about long-term care options and applying for public benefits. Services provided by the ADRC are free and available to all Dane County residents regardless of income or assets.
October is Down Syndrome Awareness Month!
October is Down Syndrome Awareness month. Down Syndrome affects about 1 in 700 births in the United States. National Down Syndrome Society observes Down Syndrome Month every October as "a forum for dispelling stereotypes, providing accurate information, and raising awareness of the potential of individuals with Down syndrome."
Down syndrome is by far the most common and best known chromosomal disorder in humans and the most common cause of intellectual disability.
The human body is made of cells. All cells contain a center, called a nucleus, in which genes are stored. Genes
carry the codes responsible for all our inherited characteristics and are grouped along rod-like structures called
chromosomes. The nucleus of each cell typically contains 23 pairs of chromosomes (half are inherited from the
mother and half from the father). Down syndrome occurs when some or all of a person’s cells have an extra full or
partial copy of chromosome 21.
The most common form of Down syndrome is known as trisomy 21. Individuals with trisomy 21 have 47 chromosomes
instead of the usual 46 in each of their cells. This condition results from an error in cell division called nondisjunction.
Prior to or at conception, a pair of 21st chromosomes in either the sperm or the egg fails to separate, passing on
both copies of the 21st chromosome instead of the typical one. As the embryo develops, the extra chromosome is
replicated in every cell of the body. This error in cell division is responsible for 95% of all cases of Down syndrome.
The two other types of Down syndrome are called mosaicism and translocation. Mosaicism (or mosaic Down syndrome)
occurs when nondisjunction of chromosome 21 takes place in one – but not all – of the initial cell divisions after
fertilization. When this occurs, there is a mixture of two types of cells, some containing the usual 46 chromosomes
and some containing 47. Those cells with 47 contain an extra chromosome 21. Mosaicism is the least common form
of Down syndrome and accounts for only about 1% of all cases. Translocation, which accounts for about 4% of cases
of Down syndrome, occurs when an additional full or partial copy of chromosome 21 breaks off during cell division
and attaches to another chromosome, usually chromosome 14. While the total number of chromosomes in the cells
remains 46, the presence of an extra full or partial chromosome 21 causes the characteristics of Down syndrome.
The cause of the extra full or partial chromosome is still unknown. It is not caused by environmental factors or anything
the parents do before or during the pregnancy. 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, because younger
women have higher fertility rates, 80% of babies with Down syndrome are born to women under the age of 35. Once
a woman has given birth to a baby with Down syndrome, her chance of having a second child with Down syndrome is
about 1 in 100, although age may also be a factor.
Maternal age, however, is not linked to the chance of having a baby with translocation. Most cases of translocation are
chance events, just like trisomy 21 and mosaicism. About a third of cases of translocation (1% of all cases of Down
syndrome) have a hereditary component – one unaffected parent is a carrier of a translocated chromosome. For this
reason, the chance of translocation occurring in a second pregnancy is higher than the chance of nondisjunction
occurring in a second pregnancy. Genetic counseling can determine if a parent is a carrier of the translocated
How is Down syndrome diagnosed?
Since many expectant parents choose to forgo prenatal tests, most cases of Down syndrome are diagnosed after the baby is born. Doctors will usually suspect Down syndrome if certain physical characteristics are present. Some of the traits common to babies with Down syndrome include:
- low muscle tone
- a flat facial profile
- a small nose
- an upward slant to the eyes
- a single deep crease across the center of the palm
- an excessive ability to extend the joints
- small skin folds on the inner corner of the eyes
- excessive space between large and second toe
Not all babies with Down syndrome have all these characteristics, and many of these features can be found, to some extent, in individuals who do not have the condition.