Down Syndrome

What is Down Syndrome?

Down syndrome (also spelled Down's syndrome in some countries) is a genetic condition in which a person is born with an extra copy of chromosome 21 — a condition known as trisomy 21. This additional genetic material affects development in ways that vary considerably from person to person.

Down syndrome is the most common chromosomal condition associated with intellectual disability, occurring in approximately 1 in 700 live births worldwide, across all ethnic, socioeconomic, and national groups. It was first described medically by British physician John Langdon Down in 1866; the chromosomal basis was identified by Jérôme Lejeune in 1959.

Types:

• Trisomy 21 — full extra copy of chromosome 21 in every cell (about 95% of cases)
• Translocation Down syndrome — extra chromosome 21 material attached to another chromosome
• Mosaic Down syndrome — extra chromosome 21 in only some cells; often associated with milder presentation

How It Presents

Down syndrome is associated with:

Cognitive:

• Intellectual disability ranging from mild to moderate in most individuals; profound in a smaller proportion
• Learning at a different pace from neurotypical development; visual learning strengths are common
• Delays in language development; receptive language (understanding) often stronger than expressive
• Increased risk of Alzheimer's disease in later adulthood (due to chromosome 21 containing the APP gene)

Physical:

• Characteristic facial features (upslanting palpebral fissures, flat nasal bridge, small ears)
• Low muscle tone (hypotonia) affecting motor development and feeding in infancy
• Congenital heart defects in approximately 40–50% of cases
• Increased risk of thyroid conditions, hearing loss, vision problems, and respiratory infections

Social and behavioural:

• Many people with Down syndrome are described as sociable, affectionate, and humorous — though these descriptions should not become stereotypes that erase individual personality

Most people with Down syndrome live into their 60s or beyond. They attend school, have friendships and relationships, work, and participate fully in community life.

Assistive Technology and Supports

• AAC — for those with significant speech difficulties, low-tech (PECS) and high-tech (SGDs) communication supports
• Easy Read materials — simplified text with supporting images, for accessible information and consent processes
• Visual schedules — support daily routine management and transitions
• Educational technology — accessible apps and interactive tools that leverage visual learning strengths
• Hearing aids — for the significant proportion with hearing loss
• Vision correction — glasses are common; eye conditions such as cataracts and strabismus may require treatment

Common Misconceptions

• "All people with Down syndrome are alike." People with Down syndrome are as individual as anyone else — varying in personality, ability, interests, and needs.
• "People with Down syndrome cannot live independently or have careers." Many adults with Down syndrome live semi-independently or independently, work in paid employment, and have rich social lives.
• "Prenatal diagnosis of Down syndrome should lead to termination." This is a values and rights question, not a medical one. Disability advocacy strongly supports the right of people with Down syndrome to live full, valued lives.

Language and Identity

Person-first language ("person with Down syndrome") is standard in most English-speaking countries. "Downs person" or "Downie" are generally considered disrespectful. The Down syndrome community has active self-advocacy organisations worldwide, with self-advocates speaking for themselves at conferences, in media, and in policy contexts.