Down syndrome

A genetic condition caused by having an extra chromosome 21 in some or all of the body’s cells. Down syndrome is marked by growth, developmental, and learning delays that vary from mild to severe. People with Down syndrome often have certain distinct physical features, such as a shorter-than-normal height, a flat face with a short nose, eyes that are slanted and almond-shaped, small ears, a short neck, a tongue that tends to stick out of the mouth, small hands and feet, and a deep line that goes across the palm of the hand. People with Down syndrome may also have muscle weakness, loose joints, heart defects, and other health problems. Having Down syndrome increases the risk of developing Alzheimer disease at an early age, usually around the age of 50, and leukemia, especially in young children. Down syndrome is usually not inherited (passed from parent to child). Also called trisomy 21.