In many cases, mental retardation is caused by genetic diseases present from conception. Down syndrome derives its name from John Langdon Down, who was the first to pinpoint the disorder. The condition is a result of a genetic abnormality in which the individual has an extra chromosome. An error in cell division during prenatal development results in a superfluous third chromosome 21. The extra chromosome is also referred to as Trisomy 21.
Down children have a particular pattern of symptoms leading to their mental retardation. Their total brain volume is generally smaller than average for their age. Measurements show a shorter diameter in the anterior-posterior section of the brain as well. The brains of Down children have other characteristic differences in shape, including a precipitous slant to the posterior sections of the brain and an underdeveloped superior temporal gyrus.
Down syndrome is the most common genetic source of mental retardation, occurring in one out of every eight hundred births. The syndrome is not associated with a particular race and is not limited to certain socioeconomic group. The chances of having a baby with Down syndrome do increase with the mother's age.
The life expectancy for an individual who has Down syndrome is significantly shorter than average at fifty-five years. This relatively short life span is twenty years longer than it was two decades ago.
Symptoms of Down syndrome include physical features that are quickly recognized by the doctor who delivers the baby. The child's eyes usually have an upward slant and they often have Brushfield spots (white spots on the iris). The child's ears might have an unusual shape and his neck is commonly shorter than usual. Additionally, the general shape of Down children's faces is full. but the profile of the face tends to be flat. Another physical feature associated with Down syndrome occurs in the hand. The palm of the hand may have a profound crease running crossways. None of these physical characteristics is definitive as a diagnostic symptom of Down syndrome. A person who has Down syndrome may not have all of these physical features, and these traits can also be found among the common population.
Diagnosing Down syndrome requires a blood test so that the characteristic chromosomal abnormality (Trisomy 21) can be identified. The necessary procedure is known as a chromosomal karyotype. The procedure takes about two weeks, most of which is required so that blood cells can be grown until there are enough to sort and test for the presence of the extra chromosome 21.
Certain medical conditions, including Alzheimer's disease, occur in the Down syndrome population with greater than normal frequency.
Just like mental retardation in general, Down syndrome is associated with a broad spectrum of intellectual and adaptive functioning. Each Down case is unique. Some individuals function quite well and demonstrate relatively good social skills, while others face profound challenges in social and intellectual situations. The Down population has a widespread reputation for possessing friendly and loving temperaments. They often express affection openly and are very endearing to other people.
