Down's syndrome

Down's syndome is disorder caused by having an extra chromosome on chromosome 21 (referred to as trisomy 21), giving a total of 47 chromosomes instead of the normal 46 in humans. Most cases of Down's syndrome are a result of a random chromosomal defect during the formation of reproductive cells, especially egg cells. An error during gamete cell division, non-disjunction, results in the cell with an abnormal number of chromosomes. This extra chromosome copy disrupts the normal course of brain and body development, thus affecting both physical development and intellectual ability. Although individuals with Down's syndrome behave and look similar, their intellectual capability varies from mild to moderately low. As sufferers age (often about the age of 50), they may often experience a progressive decline in cognitive function, which can result in an increased risk of Alzheimer's, a neurodegenerative disease that causes dementia: a gradual loss of memory, motor skills, and judgement. 

Types

There are three main types of Down's syndrome

Typical characteristics

• Flat face
• Short neck
• Abnormally shaped ears
• Poor muscle tone (hypotonia)
• Small hands and feet

Symptoms

• Heart disease
• Coeliac disease
• Eye problems
• Hearing problems
• Skeletal intestinal problems
• Dementia
• Underactive thyroid