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.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:

Trisomy 21

Before or at conception, a pair on chromosome 21 in spem or egg cells fail to seperate properly - nondisjunction, which results in an embryo with three copies of chromosome 21 instead of the usual two. 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. As the embryo develops, the extra chromosome is replicated in every cell of the body. This is the most common form, and accounts for about 95% of cases. 

Mosaic trisomy 21

This is the least common form and accounts for about 1% of cases. 

Translocation trisomy 21

Chromosome 21 becomes attached to another chromosome during gametic cells formation or during early foetal development. No genetic material is gained or lost during balanced translocation. 

Causes

To date, the cause of the extra of partial chromosome is still unknown, Maternal age is a contributory factor towards a higher risk of a baby having Down's syndrome with trisomy 21 or mosaicism. There is no conclusive scientific research to suggest that environmental factors or parental activities before or during preganancy are the causes. 

Symptoms

Physical

• Flattened face and nose
• Short neck with excess skin at the back
• Small hands and feet
• Upward slanting eyes with a skin fold from upper eyelid that covers inner corner of the eye
• Brushfield spots: white spots on coloured part of the eye 
• Abnormally shaped ears
• Poor muscle tone (hypotonia)
• Heart disease
• Congenital heart defects
• Coeliac disease
  
• Hearing problems

• Hypothyroidism

Young children are more susceptible to developmental delay. This may be a consequence of poor muscle tone, which impacts the ability to stand, balance, and sit normally, so they may reach these milestones slower than other children,

Intelletual and behavioural

• Dementia
• Delayed develop

Diagnosis

Prenatal

Chorionic villus sampling

Amniocentisis

At birth

Non-invasive prenatal testing

Karyotope analysis of newborn