Down syndrome - Guangzhou Elizabeth Women's Hospital

Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of all, or part of a third copy of chromosome 21. It is typically associated with physical growth delays, characteristic  facial features, and mild to moderate intellectual disability.The average IQ of young adult with Down syndrome is 20, equivalent to the mental age of an 8-or 9-year-old child, but this can very widely.But the parents of the affected individual are typically genetically normal. The extra chromosome occurs by random chance. This additional genetic meaterial 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 they 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.
Three Different Types of Down Syndrome:

∆ Trisomy 21 ( Nondisjunction )
∆ Translocation
∆ Mosaicism

What Cause Down Syndrome?
Regardless of the type of Down sydrome 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.However, 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.
There is no definitive scientific research that indicates that Down syndrome is caused by environment factors or the parent's 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.

What are symptoms of Down's syndrome?
Those with Down syndrome nearly always have physical and intellectual disabilities. As adults, their mental abilities are typically similar to those of an 8- or 9-year-old. They also typically have poor immune function and generally reach development milestones at a later age. They have an increased risk of a number of other health problems, including congenital heart defect, epilepsy, leukemia, thyroid diseases, and mental disorders, among others.

∆ Physical
People  with Down syndrome may have some or all of these physical characteristics: a small chin, slanted eyes, poor muscle tone, a flat nasal bridge, a single crease of the palm, and a protruding tongue due to a small mouth and relatively large tongue.Growth in height is slower and individuals with Down syndrome are at increased risk for obesity as they age.
∆ Neurological
Most individuals with Down syndrome have mild ( IQ :50 - 70 ) or moderate ( IQ :35 - 50 ) intellectual disability with some cases having severe ( IQ :20 - 35 ) difficulties. As they age, people with Down syndrome typically perform less well than their same-age peers. Some after 30 years of age may lose their ability to speak. 
Children and adults with Down syndrome are at increased risk of epileptic seizures which occur in 5-10% of children and up to 50% of adults.
∆ Senses
Hearing and vision disorders occur in more than half of people with Down syndrome. Vision problems occur in 38 to 80%. Between 20 and 50% have strabismus, in which the two eyes do not move together. 
∆ Heart
The rate of congenital heart disease in newborns with Down syndrome is around 40%. Of those with heart disease, about 80% have an atrioventricular septal defect or ventricular septal defect with the former being more common. Mitral valve problems become common as people age, even in those without heart problems at birth. Other problems that may occur include tetralogy of Fallot and patent ductus arteriosus. People with Down syndrome have a lower risk of hardening of the arteries.
∆ Fertility
Males with Down syndrome ususally do not father children, while females have lower rates of fertility relative to those who are unaffected.Fertility is estimated to be present in 30-50% of females.Menopause typically occurs at an earlier age.The poor fertility in males is thought to be due to problems with sperm development. However, it may also be related to not being sexually active.

How Is Down Syndrome Diagnosed?
There are two categories of tests for Down's syndrome that can be performed before a baby is born:screening tests and diagnostic tests.Prenatal screens estimate the chance of the fetus having Down syndrome. These tests, on the other hand, can provide adefinitive diagnosis with almost 100% accuracy. 

Guangzhou Elizabeth International Medical Center usually advise pregnancy women accept Down syndrome screening in the period of 9~13Weeks in pregnacny. Especially for those women who aged over 35 years old, the risk that their babies get Down syndrome is higher than young women. In order to confirm their babies' health, pregnancy women should go to the hospital and do regular examination.

Part of the article and pictures orginated from network.