Basics of Down Syndrome?

Basics of Down Syndrome

Down syndrome is one of the most common chromosomal conditions — occurring in approximately 1 in 700 births worldwide. It is caused by the presence of an extra copy of chromosome 21 (trisomy 21), resulting in a total of 47 chromosomes instead of the usual 46. Down syndrome is associated with characteristic physical features, intellectual disability of varying degrees, and an increased risk of certain health conditions.

Types of Down Syndrome

• Trisomy 21 (95% of cases) — every cell in the body has three copies of chromosome 21; caused by a random error in cell division (non-disjunction) during the formation of the egg or sperm

• Translocation Down syndrome (~4% of cases) — part of chromosome 21 attaches to another chromosome (usually chromosome 14); the total number of chromosomes may be 46, but the extra chromosomal material causes Down syndrome features

• Mosaic Down syndrome (~1% of cases) — only some cells have trisomy 21; individuals with mosaic Down syndrome may have milder features

Common Features

• Characteristic facial features: flat facial profile, upward-slanting eyes, small ears, protruding tongue

• Low muscle tone (hypotonia) at birth

• Intellectual disability (mild to moderate in most cases)

• Developmental delays in speech, motor skills, and social development

• Increased risk of congenital heart defects (present in ~50% of cases), thyroid disorders, hearing loss, and vision problems

Prenatal Screening and Diagnosis

Down syndrome can be detected prenatally through screening tests (NIPT, NT scan, double/triple/quadruple marker) and confirmed through diagnostic tests (amniocentesis, chorionic villus sampling). NIPT (Non-Invasive Prenatal Testing) has a sensitivity of over 99% for trisomy 21 and can be performed from 10 weeks of pregnancy. Genetic counselling is recommended for all couples with a positive screening result.

Living with Down Syndrome

With appropriate support, early intervention, and inclusive education, people with Down syndrome lead fulfilling, meaningful lives. Life expectancy has increased dramatically — from 25 years in the 1980s to over 60 years today. Early therapy (speech, occupational, physiotherapy) and regular medical monitoring make a significant difference to outcomes.