Down

Down Syndrome 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 a young adult with Down syndrome is 50, equivalent to the mental age of an 8 or 9 year-old child, but this varies widely.

Causes

Down syndrome is caused by having three copies of the genes on chromosome 21, rather than the usual two. The parents of the affected individual are typically genetically normal. The extra chromosome occurs by chance. The probability increases from less than 0.1% in 20-year-old mothers to 3% in those age 45. The extra chromosome is believed to occur by chance, with no known behavioral activity or environmental factor that changes the probability.

Symptoms

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. These airway changes lead to obstructive sleep apnea in around half of those with Down syndrome.

Treatment

There is no cure for Down syndrome. Education and proper care have been shown to improve quality of life. Some children with Down syndrome are educated in typical school classes, while others require more specialized education. Some individuals with Down syndrome graduate from high school, and a few attend post-secondary education.

See Also

• Genetic disorders
• Chromosome 21
• Intellectual disability

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