Down Syndrome

Down syndrome is a genetic disease that a person is born with. DS is the most common genetic disorder. 1 in every 800 to 1,000 babies born is diagnosed with the disorder. There is no relationship between DS and diet, drugs, economic status, or life style. Some evidence suggests that it is a little more common in families with Alzheimer's disease in one or more family members. Although Down syndrome does not only occur in babies born to older mothers, but babies born to mothers over 35 are more at risk. Down Syndrome can be caused by three factors, nondisjunction, mosaicism, and translocation

The most common cause is nondisjunction. About 95% of people born with Down syndrome have nondisjunction as the cause. Nondisjunction occurs when chromosome number 21 doesn’t separate from during meiosis while creating an egg or sperm, although it is most commonly the egg. This results in an embryo with three number 21 chromosomes rather than the normal two. As this cell divides during mitosis each body cell of the embryo will have three number 21 chromosomes. This defect where there are three chromosomes is called a trisomy pair. Although most fetuses that have this defect live, about three quarters of fetuses with DS die before birth.

Mosiacism is caused by nondisjunction in one of the initial cell division. This causes some cells to have 46 chromosomes and some have 47 chromosomes. Mosiacism is rare and accounts only for 1 or 2% of all Down syndrome cases.

Translocation accounts for 3 to 4% of all Down syndrome cases. Translocation occurs when a piece of chromosome 21 breaks off and attaches to another chromosome. It is the extra part of chromosome 21 that causes the defects associated with DS.

Down Syndrome is associated with many problems for the child. Many of these defects are physical. Children with Down syndrome often have low muscle tone, a small nose with a flattened nasal bridge, and eyes with an upward slant, odd shaped ears, and a large tongue in relation to the mouth size. Some other effects caused by DS are slight to moderate mental retardation, and congenital heart problems. It is also estimated that about 25% of all people born with DS will develop Alzheimer’s when they reach about 35 years old. People with DS are also 15 to 20 times more likely to develop Leukemia.

Although there are no symptoms to detect the disease there are ways that a mother can find out if her baby has DS. Screening tests estimate the chance of a woman having a baby with DS. These screening tests are done in conjunction with sonograms, and usually detect approximately 60% of Down syndrome cases. Doctors can also perform other tests to determine if a fetus will be born with DS. These tests include chorionic villus sampling, amniocentesis, percutaneous umbilical blood sampling. These tests are 98 to 99% accurate, but they do however carry the slight risk of miscarriage.

There is no known treatment for Down syndrome. Gene therapy has been attempted but, with no results. The use of karyotyping which is shown above is allowing scientists to further examine chromosome 21 and figure out how Down syndrome is caused and how to cure it.

Although people living with Down syndrome have many problems they can still go on and live a normal life. Especially in recent years, advances in care for people with DS have been made. No longer are people with this disease put in institutions. Now they are able to live at home and often attend regular schools. Also, people with Down syndrome are beginning to have relationships. Many now marry, but they usually don’t have children. This is because most males with Down syndrome are thought to be sterile. There is only 1 record of a man with Down syndrome ever fathering a child.

Because DS is the most common genetic disease, scientists have lately focused a lot of attention on its causes and are working toward finding a treatment. Until we can find a definite treatment we must learn how to cope and care for those with DS. There is hope however, because in recent years, people with Down syndrome are now living into their 50’s, where before the life expectancy was about nine years old.