Down syndrome

Down syndrome (also called Trisomy 21) is a genetic disorder. It is the leading cause of cognitive impairment. It is associated with mil to moderate learning disabilities developmental delays, characteristic facial features, and low muscle tone in early infancy. Many individuals also have heart defect, leukemia, early-onset Alzheimer's disease ,gastro-intestinal problems, and other health issues. The symptoms of Down syndrome range from mild to severe.

The chromosome basics of Down syndrome

In Down syndrome, an individual most often inherits two copies of chromosome 21 from the mother and one chromosome 21 from the father for a total of three chromosomes 21. The disorder is also called trisomy 21. About 95% of individuals with Down syndrome inherit an entire extra chromosome 21.

Approximately 3% to 4% of individuals with Down syndrome do not inherit an entire extra chromosome 21, but just some extra chromosome 21 genes, which are attached to another chromosome (usually chromosome 14). This is called a translocation.

About 2% to 4% of people with Down syndrome inherit additional genes from chromosome 21, but not in every cell of the body. This is known as mosaic Down syndrome.

Characteristic feature of Down syndrome

• a flattened face and nose, a short neck, a small mouth sometimes with a large, protruding tongue, small ears, upward slanting eyes that may have small skin folds at the inner corner (epicanthal fold);
• white spots (also known as Brushfield spots) may be present on the colored part of the eye (iris);
• the hands are short and broad with short fingers, and with a single crease in the palm;
• poor muscle tone and loose ligaments are also common; and
• development and growth is usually delayed and often average height and developmental milestones are not reached
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