Each cell of the human body contains 46 chromosomes. Down syndrome occurs when a person has a genetic defect in which the cells contain 47 chromosomes. These individuals have an extra copy of chromosome 21. The presence of this extra chromosome causes abnormal development of the brain and the body. Down syndrome is the most common human birth defect. It is present from the type of birth and not acquired in life. There is also no cure for Down syndrome.
Symptoms of Down syndrome vary among affected individuals and can range from mild to severe. The following signs and symptoms are characteristic of Down syndrome:
- Children affected with Down syndrome have a common characteristic appearance with abnormally shaped head, upward slanting eyes, small ears, small mouth, flat face and nose, short neck, short arms and short legs. Affected children also have a decreased muscular tone at birth. Their hands are wide, short and have a single crease on the palm.
- All affected individuals show various degrees of mental retardation.
- Physical development is slower than normal and many children with Down syndrome do not reach the average adult height.
- Almost all organs of the body are affected in Down syndrome. Complications include heart defects, dementia, eye problems (e.g., cataract), gastrointestinal problems, hearing problems and ear infections, hip and joint dislocations, sleep apnea and breathing problems, hypothyroidism, diabetes and infertility.
About 95% of individuals affected with Down syndrome contain 47 chromosomes in all their cells due to the presence of an extra copy of chromosome 21. In other affected individuals, only some cells of the body inherit an extra copy of chromosome 21 – a condition termed as mosaicism. A minority of individuals affected with Down syndrome may have extra copies of only a part of the chromosome 21. The exact reason for the inheritance of an extra copy of a chromosome during cell division is not known.
However, advanced maternal age at the time of childbirth is the most important risk factor. The incidence of Down syndrome in unborn babies increases dramatically if the mother’s age is above 35 years at the time of childbirth. If the first child has Down syndrome, then the risk of the second child having it also increases. Prenatal genetic tests for Down syndrome in unborn fetuses are now available and are recommended for women over 35 who are planning on having a baby.
There is no cure for Down syndrome. However, individuals with Down syndrome can lead healthy, happy and productive lives with proper supervision. Individuals affected with Down syndrome usually have a reduced lifespan and often do not survive past 50 years of age. This is mostly due to the heart defects and other abnormalities associated with Down syndrome.
However, treatment options are available for many of the associated abnormalities of Down syndrome. For example, heart defects could be corrected surgically, hypothyroidism could be corrected by hormone replacement therapy, eye and ear problems could be managed with regular checkups, and diabetes could be managed with drugs and lifestyle changes.
In addition, speech therapy, physical therapy and occupational therapy are available for individuals with Down syndrome.