Down syndrome, also known as Trisomy 21, is a genetic condition where an individual has an extra chromosome or an additional segment of a chromosome. This extra genetic material affects the development of the baby’s body and brain, leading to both mental and physical challenges throughout their life. While individuals with Down syndrome may share certain physical traits and behaviors, each person possesses unique abilities and characteristics.

Down syndrome is a relatively common birth defect, affecting approximately 1 in 700 babies born in the United States each year and between 1 in 1,000 to 1 in 1,100 live births worldwide.

CDC (U.S Center For Disease Control And Prevention)

Causes

Down syndrome can be caused by three factors:

• Trisomy 21: This is the most common cause, affecting approximately 95% of individuals with Trisomy 21. In this condition, there are three copies of chromosome 21 instead of the usual two. Typically, during fertilization, each egg and sperm carries one chromosome from each pair. However, in trisomy 21, chromosome 21 fails to separate properly, resulting in an extra chromosome. This extra chromosome usually originates from the egg, accounting for 95 to 97% of cases.
• Translocation: Responsible for about 3 to 4% cases, translocation occurs when a fragment of chromosome 21 attaches to another chromosome. In approximately half of these cases, one parent carries this extra chromosome 21 material in a “balanced” or hidden form.
• Mosaicism: This rare form of Down syndrome, affecting about 1 to 2% of individuals, involves having an extra chromosome 21 in some cells but not others. The unaffected cells have the standard pair of chromosome 21.

Symptoms

Symptoms of Down syndrome vary widely from person to person, and individuals with this condition may encounter different challenges at various stages of life. Typically, people with Trisomy 21 experience mild to moderate intellectual disabilities and often face developmental delays, such as starting to talk later than their peers.

Common physical characteristics of Down syndrome include:

• Flattened face
• Small head
• Short neck
• Protruding tongue
• Upward slanting eyelids (palpebral fissures)
• Unusually shaped or small ears
• Poor muscle tone
• Broad, short hands with a single crease in the palm

Diagnosed

The American College of Obstetricians and Gynecologists recommends offering both screening and diagnostic tests for Down syndrome to all pregnant women, regardless of age.

Screening Tests:

These tests assess the likelihood of your baby having Down syndrome but cannot confirm a diagnosis. They help determine if further diagnostic testing is needed.

• First Trimester Combined Test: Includes a blood test measuring pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (HCG) levels, along with a nuchal translucency ultrasound to measure fluid at the back of the baby’s neck.
• Integrated Screening Test: Conducted in two parts—early pregnancy (blood test and nuchal translucency ultrasound) and later (quad screen measuring alpha-fetoprotein, estriol, HCG, and inhibin A).

Diagnostic Tests:

Confirm whether your baby has Down syndrome.

• Chorionic Villus Sampling (CVS): Performed between 10 and 13 weeks of pregnancy, this test involves analyzing cells from the placenta to check fetal chromosomes. The risk of miscarriage is very low.
• Amniocentesis: Conducted after 15 weeks of pregnancy, this test involves extracting a sample of amniotic fluid to analyze fetal chromosomes. It also carries a very low risk of miscarriage.
• Preimplantation Genetic Diagnosis: For couples undergoing IVF, this test checks embryos for genetic conditions before implantation.

Post-Birth Diagnosis:

Professionals often initially identify Down syndrome based on physical features after birth. However, a chromosomal karyotype test using a blood sample confirms the diagnosis by checking for an extra chromosome 21.

Treatments for Down syndrome?

Treatment for Down syndrome focuses on addressing physical and intellectual challenges:

• Physical Therapy: Helps improve muscle tone and mobility, aiding in actions like rolling over and walking.
• Heart Health: Since 40-60% of babies with Trisomy 21 have heart defects, they undergo heart checks with an electrocardiogram and echocardiogram. If a defect is found, a pediatric cardiologist or cardiac surgeon may be consulted for management or surgery.
• Surgical Interventions: Surgery may be needed to address swallowing issues or bowel blockages, usually resolving these problems.
• Infection Management: Frequent colds and ear infections are treated early to prevent hearing loss and chronic issues.
• Thyroid Testing: Annual thyroid level testing is recommended due to a higher risk of thyroid problems.
• Eye Care: Eye issues like cataracts or strabismus may require surgical intervention.
• Feeding Support: Occupational and speech therapists, along with breastfeeding consultants, can assist with feeding difficulties.
• Developmental Support: Early intervention programs and preschool therapies help with motor, language, and social skills. While intelligence varies, many adults with Trisomy 21 work and live independently.

Drugs and Supplements

Individuals with Down syndrome have been treated with amino acids and other brain-influencing medications, but the outcomes of these trials have been inconsistent and sometimes harmful. While newer psychoactive drugs have emerged, their safety and effectiveness for this population remain unverified due to a lack of rigorous scientific testing.

Researchers have limited research into treatments for dementia associated with Trisomy 21 due to small sample sizes and inconclusive results. While generally considering antioxidants safe, studies have failed to demonstrate their efficacy in improving cognitive decline.

DS-Connect^®: Registry

DS-Connect® is an online registry designed to gather health data and connect individuals with Down syndrome to research opportunities. Managed by NICHD and the Trisomy 21 Consortium, this confidential resource provides surveys in English and Spanish to collect basic health information.

Launched in 2018 under the NIH INCLUDE Project, DS-Connect® aims to improve health and quality of life for people with Trisomy 21 by boosting participation in clinical research and expanding understanding of associated health conditions. The initiative enhances coordination of Trisomy 21 research across NIH.

Related Issues

• Is there a connection between ADHD and Down syndrome?
• Can people with Down syndrome develop Alzheimer’s disease?
• What eye problems are common among people with Down syndrome?
• How does Down syndrome interact with autism?
• What ear, nose, and throat issues are common in people with Down syndrome?
• Are there specific endocrine conditions related to Down syndrome?
• What mental health concerns are prevalent in individuals with Down syndrome?
• What are the considerations for relationships and sexuality in people with Down syndrome?

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