Down's syndrome

Down’s syndrome is one of the best-known causes of a learning disability. It is a genetic condition, resulting from either an extra chromosome or extra genetic material from chromosome 21.

There are three different types of Down’s syndrome: trisomy 21 (the most common type at around 90-95%), translocation (around 3%) and mosaicism (around 1-5%).


Down’s syndrome affects people in different ways. It is generally associated with cognitive impairment, physical characteristics and certain health issues.

There is a wide range of cognitive impairment, with some young people attending mainstream school and even sitting GCSE exams, and others having a high degree of learning disability.

How many people have Down’s syndrome?

It is estimated that in developed countries, approximately 1 in 1000 babies are born with Down’s syndrome. 

Maternal age

Most babies with Down's syndrome are born to women under 35, but older women are more likely to give birth to a child with the condition.

Related health issues

People with Down’s syndrome may have a variety of related health issues. Generally, the main health problems are:

  • respiratory system – a number of people breathe mainly or solely through their mouths, which can result in sleeping problems (sleep apnoea). Very young children can be more prone to chest infections, but this disposition reduces when they become more active.
  • heart – around 40-50% of babies with Down’s syndrome are born with a congenital heart condition, some of which require heart surgery. For more information see the Down’s Heart Group website.
  • ears and hearing – hearing problems are common, and this can then affect speech and communication.
  • eyes and vision – visual problems again are very common, with many people requiring glasses.
  • thyroid disorders – people may experience overactive or underactive thyroid glands (with underactive being more common) and extra care must be taken to ensure that these are detected.
  • ageing – people with Down’s syndrome tend to age earlier and have a greater risk of developing dementia.