Down syndrome

Overview

Down syndrome, also known as trisomy 21, is a genetic disorder caused by the presence of an extra copy of chromosome 21. It is one of the most common chromosomal conditions, occurring in approximately 1 in 700 live births worldwide. Down syndrome affects physical growth, facial features, and intellectual development to varying degrees. While it is a lifelong condition, early intervention, medical care, and educational support can greatly improve quality of life and functional abilities.

Causes

Down syndrome is caused by an extra chromosome 21, resulting in three copies (trisomy) instead of the usual two. This leads to overexpression of certain genes, disrupting normal development. There are three types of Down syndrome:

• Trisomy 21 (95% of cases): Every cell in the body has three copies of chromosome 21 due to a random error during cell division.

• Translocation (3–4%): Part of chromosome 21 becomes attached (translocated) to another chromosome. This form can be inherited.

• Mosaicism (1–2%): Some cells have three copies of chromosome 21, while others have the usual two. Symptoms may be milder in mosaic cases.

The risk of Down syndrome increases with maternal age, especially in women over 35, though it can occur at any age.

Symptoms

Individuals with Down syndrome often share certain physical and developmental features, though the severity can vary. Common characteristics include:

• Facial features: Flat facial profile, upward slanting eyes, small ears, and a protruding tongue.

• Hypotonia: Poor muscle tone, especially in infancy.

• Short stature: Slower growth and shorter height.

• Single palmar crease: A deep crease across the center of the palm.

• Developmental delays: Delayed milestones in motor skills, speech, and cognition.

• Intellectual disability: Ranges from mild to moderate; affects learning, reasoning, and adaptive skills.

• Congenital heart defects: Present in about 40–50% of cases.

• Other health issues: Including hearing loss, vision problems, thyroid disorders, and increased risk of infections.

Diagnosis

Down syndrome can be diagnosed prenatally or after birth. Common diagnostic methods include:

• Prenatal screening tests: Blood tests and ultrasounds that assess the likelihood of Down syndrome but do not confirm it.

• Prenatal diagnostic tests:

  • Chorionic villus sampling (CVS): Performed around 10–13 weeks of pregnancy.

  • Amniocentesis: Performed after 15 weeks to analyze fetal chromosomes.

• Postnatal diagnosis: Physical features at birth may suggest Down syndrome, but confirmation is done via a karyotype test to examine the baby’s chromosomes.

Treatment

There is no cure for Down syndrome, but comprehensive management can greatly enhance development and quality of life. Treatment focuses on addressing individual medical, educational, and developmental needs:

• Early intervention: Physical, speech, and occupational therapy starting in infancy to support developmental milestones.

• Medical care: Monitoring and treatment for heart defects, thyroid issues, hearing/vision problems, and other associated conditions.

• Educational support: Individualized education programs (IEPs) tailored to the child's learning abilities.

• Social and emotional support: Encouraging participation in community, recreational, and peer activities.

• Transition planning: Guidance for moving into adult education, employment, and independent or supported living.

Prognosis

The prognosis for individuals with Down syndrome has improved dramatically over the past few decades due to advances in medical care and early support services. Many people with Down syndrome live into their 60s or beyond and enjoy meaningful lives. While they may face challenges in learning and health, individuals with Down syndrome can attend school, hold jobs, form relationships, and participate actively in society with the right support and opportunities.