Down's syndrome

Down's syndrome is a condition associated with a chromosome abnormality, usually trisomy of chromosome 21.

A boy with Down syndrome using cordless drill to assemble a book case

Signs and symptoms

Symptoms and findings include a small, flattened skull, short, flat-bridged nose, an abnormal fold at the inner edge of the eyes, short fingers and toes, and moderate to severe mental retardation.

What are chromosomes?

Chromosomes carry the genes that tell the body to develop in certain ways and to perform certain functions. Most cells of the human body contain 23 pairs of chromosomes—one set of chromosomes from each parent— for a total of 46 chromosomes. People with Down syndrome have either a full or partial extra copy of chromosome 21, for a total of 47 chromosomes. (The syndrome is sometimes called 47,XX,+21 or 47,XY,+21 to indicate the extra chromosome 21.)

Extra chromosome

The extra chromosome disrupts the normal course of development and results in the physical features and intellectual and developmental disabilities associated with the syndrome.

Different degrees

The degree of intellectual disability in people with Down syndrome varies but is usually mild to moderate. Generally, children with Down syndrome reach key developmental milestones later than other children.

Down's syndrome Resources
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