Overview
Down syndrome, also known as trisomy 21, is the most common chromosomal disorder and the leading genetic cause of intellectual disability. It results from the presence of an extra full or partial copy of chromosome 21. This can occur through three mechanisms: free trisomy 21 (the most common, accounting for about 95% of cases), Robertsonian translocation involving chromosome 21, or mosaicism where only some cells carry the extra chromosome. The condition is typically associated with advancing maternal age, though it can occur at any maternal age. Down syndrome affects multiple body systems. Characteristic features include a distinctive facial appearance with flat facial profile, upslanting palpebral fissures, epicanthal folds, small ears, and a flat nasal bridge. Individuals typically have generalized hypotonia (low muscle tone), short stature, and varying degrees of intellectual disability ranging from mild to moderate. Congenital heart defects occur in approximately 40-50% of affected individuals, with atrioventricular septal defects being the most common. Other associated conditions include gastrointestinal anomalies (such as duodenal atresia or Hirschsprung disease), hypothyroidism, hearing loss, vision problems, increased susceptibility to respiratory infections, and a significantly elevated risk of acute lymphoblastic leukemia and acute myeloid leukemia in childhood. Individuals also have an increased risk of early-onset Alzheimer disease, typically beginning in the fourth or fifth decade of life. There is no cure for Down syndrome, but early intervention programs including physical therapy, occupational therapy, and speech therapy significantly improve developmental outcomes. Medical management focuses on screening for and treating associated conditions, including echocardiography for congenital heart defects, thyroid function monitoring, audiological and ophthalmological evaluations, and developmental assessments. Surgical correction of heart defects and gastrointestinal anomalies has dramatically improved life expectancy, which now exceeds 60 years in many developed countries. Ongoing research is exploring targeted therapies to improve cognitive function, though none are currently established as standard of care.
Also known as:
Clinical phenotype terms— hover any for plain English:
Sporadic
Usually appears on its own, not inherited from a parent
Neonatal
Begins at or shortly after birth (first 4 weeks)
FDA & Trial Timeline
10 eventsMichael Rafii, MD, PhD — PHASE4
Northwestern University — NA
Ohio State University — PHASE2
National Institute of Allergy and Infectious Diseases (NIAID)
Brigham and Women's Hospital — PHASE1
Sumitomo Pharma America, Inc. — PHASE1
Riphah International University — NA
Hospices Civils de Lyon
UNC Lineberger Comprehensive Cancer Center — NA
Beni-Suef University — NA
Data sourced from FDA regulatory filings and ClinicalTrials.gov. Updated periodically.
Treatments
No FDA-approved treatments are currently listed for Down syndrome.
20 clinical trialsare actively recruiting — trials can provide access to cutting-edge therapies.
View clinical trials →Rare Disease Specialist
Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Down syndrome.
Community
No community posts yet. Be the first to share your experience with Down syndrome.
Start the conversation →Latest news about Down syndrome
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Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Common questions about Down syndrome
What is Down syndrome?
Down syndrome, also known as trisomy 21, is the most common chromosomal disorder and the leading genetic cause of intellectual disability. It results from the presence of an extra full or partial copy of chromosome 21. This can occur through three mechanisms: free trisomy 21 (the most common, accounting for about 95% of cases), Robertsonian translocation involving chromosome 21, or mosaicism where only some cells carry the extra chromosome. The condition is typically associated with advancing maternal age, though it can occur at any maternal age. Down syndrome affects multiple body systems. C
How is Down syndrome inherited?
Down syndrome follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Down syndrome typically begin?
Typical onset of Down syndrome is neonatal. Age of onset can vary across affected individuals.
Are there clinical trials for Down syndrome?
Yes — 20 recruiting clinical trials are currently listed for Down syndrome on UniteRare. See the clinical trials section on this page for phase, sponsor, and site details sourced from ClinicalTrials.gov.
Which specialists treat Down syndrome?
25 specialists and care centers treating Down syndrome are listed on UniteRare, sourced from ClinicalTrials.gov principal investigators, published research, and the NPPES NPI registry.