Overview
Uniparental disomy of chromosome 21 (UPD 21) is an extremely rare genetic condition in which a person inherits both copies of chromosome 21 from one parent instead of receiving one copy from each parent. This entry is labeled as 'OBSOLETE' in the Orphanet classification, meaning it is no longer maintained as a separate disease entity in that database, likely because it has been reclassified or merged with other conditions. However, the underlying genetic event — uniparental disomy — can still have clinical significance. When both copies of chromosome 21 come from one parent, problems can arise in two main ways. First, if the parent who contributed both copies carries a recessive disease gene on chromosome 21, the child may develop that recessive condition because they have two copies of the faulty gene. Second, there may be effects related to genomic imprinting, although chromosome 21 is not strongly associated with known imprinted genes. In some cases, UPD 21 may have no noticeable clinical effects at all. The symptoms and severity of UPD 21 depend entirely on whether harmful recessive gene variants are present on the inherited chromosome. Some individuals may show no symptoms, while others could present with features that overlap with autosomal recessive conditions linked to genes on chromosome 21. There is no specific treatment for UPD 21 itself; management focuses on any symptoms or conditions that arise as a result of the genetic change.
Also known as:
Key symptoms:
Symptoms vary widely depending on which genes are affectedSome individuals may have no symptoms at allPossible developmental delay if recessive disease genes are unmaskedPossible intellectual disability in some casesGrowth problems in some casesFeatures of specific autosomal recessive disorders linked to chromosome 21 genes
Sporadic
Usually appears on its own, not inherited from a parent
Variable
Can begin at different ages, from infancy through adulthood
Treatments
No FDA-approved treatments are currently listed for OBSOLETE: Uniparental disomy of chromosome 21.
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Specialists
View all specialists →No specialists are currently listed for OBSOLETE: Uniparental disomy of chromosome 21.
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 OBSOLETE: Uniparental disomy of chromosome 21.
Community
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Caregiver Resources
NORD Caregiver Resources
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Mental Health Support
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.Does my child's UPD 21 involve any known disease-causing gene variants?,Is the UPD from the mother (maternal) or father (paternal), and does it matter?,Are there any recessive conditions on chromosome 21 we should screen for?,What is the chance of this happening again in a future pregnancy?,Should other family members be tested?,Will my child need any ongoing monitoring or follow-up?,Should we see a genetic counselor to discuss family planning?
Common questions about OBSOLETE: Uniparental disomy of chromosome 21
What is OBSOLETE: Uniparental disomy of chromosome 21?
Uniparental disomy of chromosome 21 (UPD 21) is an extremely rare genetic condition in which a person inherits both copies of chromosome 21 from one parent instead of receiving one copy from each parent. This entry is labeled as 'OBSOLETE' in the Orphanet classification, meaning it is no longer maintained as a separate disease entity in that database, likely because it has been reclassified or merged with other conditions. However, the underlying genetic event — uniparental disomy — can still have clinical significance. When both copies of chromosome 21 come from one parent, problems can aris
How is OBSOLETE: Uniparental disomy of chromosome 21 inherited?
OBSOLETE: Uniparental disomy of chromosome 21 follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.