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GeneticICD-10: Q90.9Occurs in approximately 1 in 700 live births

Down Syndrome

Also known as: Trisomy 21, Down's Syndrome

Down syndrome is a genetic condition caused by the presence of an extra copy of chromosome 21 (trisomy 21), which affects physical development, facial features, and intellectual ability. It is the most common chromosomal condition, occurring in about 1 in every 700 births. With advances in medical care, education, and support services, people with Down syndrome are living longer, healthier, and more fulfilling lives than ever before.

Symptoms

Characteristic facial features (flattened face, upward-slanting eyes, small ears)
Short stature and short neck
Low muscle tone (hypotonia) in infancy
Intellectual disability (mild to moderate)
Single crease across the palm (simian crease)
Small hands and feet
Developmental delays
Speech and language difficulties

Causes

  • Trisomy 21: extra copy of chromosome 21 in all cells (95% of cases)
  • Translocation: extra chromosome 21 material attached to another chromosome (3-4%)
  • Mosaicism: extra chromosome 21 in only some cells (1-2%)

Risk Factors

  • Maternal age over 35 (risk increases significantly after 35)
  • Having had a previous child with Down syndrome
  • Being a carrier of a translocation involving chromosome 21

Diagnosis

  • Prenatal screening (first trimester combined test, cell-free DNA testing)
  • Prenatal diagnostic testing (amniocentesis or chorionic villus sampling)
  • Karyotype analysis after birth to confirm trisomy 21
  • Postnatal clinical assessment of characteristic features

Treatment

  • Early intervention programs (physical, speech, and occupational therapy)
  • Special education services and individualized learning plans
  • Treatment of associated medical conditions (heart defects, thyroid problems)
  • Regular health monitoring for common complications
  • Social skills training and community integration support
  • Cardiac surgery for congenital heart defects (occurs in ~50% of cases)

Prevention

  • Down syndrome cannot be prevented as it is a chromosomal condition
  • Genetic counseling can help families understand risk factors
  • Prenatal testing provides information for planning and preparation

When to See a Doctor

  • Your newborn shows signs consistent with Down syndrome
  • You are pregnant and want to discuss prenatal screening options
  • A child with Down syndrome develops new symptoms (hearing loss, thyroid problems)
  • You want to discuss early intervention services for your child

Frequently Asked Questions

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Medical Disclaimer: This content is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider.

Content reviewed against peer-reviewed medical literature and clinical guidelines. Read our editorial standards.