down syndrome

Overview
Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21 (known as trisomy 21). It affects a person’s physical development, intellectual abilities, and overall health. Individuals with Down syndrome typically have distinct facial features, mild to moderate intellectual disability, and may have various medical conditions.

Why It’s Important
Down syndrome is the most common chromosomal condition diagnosed in the U.S. Early intervention, medical care, and supportive therapies can greatly improve quality of life, but without proper support, individuals may face significant developmental and health challenges.

Quick Facts

  • Affects approximately 1 in 700 babies born in the U.S.

  • Risk increases with maternal age, especially after age 35

  • Lifelong condition, but life expectancy has increased to 60+ years with medical care

  • Types of Down syndrome:

    • Trisomy 21 (95% of cases)

    • Translocation (4%)

    • Mosaicism (1%)

What Happens in the Body
An extra chromosome 21 affects cell division, leading to delayed development, intellectual disability, and abnormal growth patterns. It can impact organ function, especially the heart and digestive system, and alters the way the brain and body develop over time.

Common Signs and Symptoms

  • Flattened facial features

  • Almond-shaped eyes that slant upward

  • Small head, ears, and mouth

  • Short neck and short stature

  • Poor muscle tone (hypotonia)

  • Developmental delays (walking, talking)

  • Mild to moderate intellectual disability

  • Congenital heart defects (in nearly 50% of cases)

  • Increased risk of hearing loss, vision problems, thyroid issues

Diagnosis

  • Prenatal screening tests (e.g., blood tests, nuchal translucency ultrasound)

  • Diagnostic tests during pregnancy:

    • Chorionic villus sampling (CVS)

    • Amniocentesis

  • After birth: physical exam followed by karyotype blood test to confirm extra chromosome

  • Genetic counseling is often recommended for families

Treatment and Management

  • No cure, but supportive care improves health and development

  • Early intervention programs (speech, occupational, and physical therapy)

  • Special education services

  • Regular medical monitoring for heart, thyroid, hearing, vision, and growth

  • Some may require surgery for congenital conditions

  • Emphasis on inclusive care, social support, and independent living skills

Risks and Complications

  • Congenital heart disease

  • Sleep apnea

  • Hearing and vision impairments

  • Higher risk of infections due to immune system differences

  • Thyroid dysfunction, particularly hypothyroidism

  • Increased risk of leukemia and Alzheimer’s disease at earlier ages

Who Is at Risk

  • Babies born to older mothers, especially over 35

  • Parents who are carriers of translocation

  • No known environmental or lifestyle cause

Related Conditions

  • Congenital heart defects

  • Thyroid disorders

  • Leukemia (increased childhood risk)

  • Alzheimer’s disease (early onset more common)

When to See a Doctor

  • During pregnancy, if screening tests suggest risk

  • Immediately after birth if Down syndrome is suspected

  • Ongoing medical care is essential—see pediatricians, cardiologists, ENT specialists, and developmental experts regularly

  • Behavioral or health changes in adulthood may require neurologic or psychiatric evaluation

Last Updated: June 21, 2025