Down Syndrome

Introduction 

Down syndrome is the name for the pattern of physical features and disorders that usually occur from an extra 21st chromosome. Chromosomes are the materials that store people's genetic information.

What is going on in the body?

Because people who have Down syndrome have an extra chromosome, the body's natural balance is upset. This upset in balance leads to various birth defects and problems of growth and development. Many of the birth defects in people who have Down syndrome are like those seen in other children. People with Down syndrome simply are likely to have birth defects more often than others.

What are the causes and risks of the condition?

Down syndrome is usually caused by an extra 21st chromosome. Most people have 46 chromosomes in each cell of their bodies. These chromosomes exist in pairs, for a total of 23 pairs. The pair associated with Down syndrome is called pair 21. Why an extra copy of this chromosome causes the features of the Down syndrome is not known.
The genetic material on the 21st chromosome pair directs the formation of compounds that the body needs to perform various functions and for normal development. The overload of information caused by the extra copy leads to the Down syndrome. Scientists have recently identified 99.7% of the genes on this chromosome. This knowledge may lead to a better understanding of the syndrome and, perhaps, even treatments for some of the effects.
Down syndrome occurs in roughly 1 of every 750 births. There is a strong link between the risk of Down syndrome and the age of the mother. The risk of having a child with Down syndrome is less than 1 in 2,500 among young women. This risk increases to roughly 1 in 350 when women reach 35 years of age. After age 45, the risk is roughly 1 in 25.

What are the signs and symptoms of the condition?

The following characteristics can be seen in people with Down syndrome:

smaller-than-average physical size

poor muscle tone, which tends to improve somewhat over time

a small head, the back of which is flatter than average

flat facial profile

upward slant of the eye slits

an extra fold of skin at the inner corners of the eyes

small mouth with a tendency to protrude the tongue

small hands with short fingers and a single crease across the palms

congenital heart disease, or heart defects that are present at birth

learning disabilities

an IQ that is rarely higher than 50 (with normal IQ being around 100)

faster aging process, with a tendency to develop diseases of aging, such as Alzheimer's disease, at a relatively early age  

How is the condition diagnosed?

Down syndrome may be suspected at birth when certain physical features or defects are present. A chromosome analysis, however, confirms the diagnosis.
There are also tests that screen for Down syndrome during pregnancy. A blood test known as the triple screen measures the levels of certain chemicals in a pregnant woman's blood. These chemicals are estriol, human chorionic gonadotropin, and alpha-fetoprotein. When the chemicals are out of balance, there is a risk that the fetus has Down syndrome.
Other tests can be ordered to confirm the diagnosis of Down syndrome. These tests analyze the chromosomes of tissue taken from the fetus. These tests include chorionic villus sampling and amniocentesis.