Overview
Uniparental disomy of chromosome 20 (UPD 20) is a very rare genetic condition in which a child receives both copies of chromosome 20 from one parent instead of one copy from each parent. This entry is labeled 'OBSOLETE' in Orphanet, meaning it has been retired or reclassified, often because the condition has been merged into a broader or more specific category. However, the underlying concept remains clinically relevant. When both copies of chromosome 20 come from the mother (maternal UPD 20), the most recognized consequence is Pseudohypoparathyroidism type 1B, which affects how the body responds to certain hormones, particularly parathyroid hormone. When both copies come from the father (paternal UPD 20), the clinical picture may differ due to imprinting — a process where certain genes are active or silent depending on which parent they came from. Symptoms can include growth problems, feeding difficulties in infancy, and developmental delays. Because this is an extremely rare condition, treatment is mainly supportive and directed at the specific symptoms each patient experiences. Genetic counseling is strongly recommended for affected families to understand recurrence risks and the specific type of UPD involved.
Also known as:
Key symptoms:
Short stature or growth restrictionFeeding difficulties in infancyDevelopmental delayLow calcium levels in the bloodResistance to parathyroid hormoneSmall for gestational age at birthFailure to thriveMild intellectual disabilityObesity in some casesBone abnormalities
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 20.
View clinical trials →Clinical Trials
View all trials with filters →No actively recruiting trials found for OBSOLETE: Uniparental disomy of chromosome 20 at this time.
New trials open frequently. Follow this disease to get notified.
Specialists
View all specialists →No specialists are currently listed for OBSOLETE: Uniparental disomy of chromosome 20.
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 20.
Community
No community posts yet. Be the first to share your experience with OBSOLETE: Uniparental disomy of chromosome 20.
Start the conversation →Latest news about OBSOLETE: Uniparental disomy of chromosome 20
No recent news articles for OBSOLETE: Uniparental disomy of chromosome 20.
Follow this condition to be notified when news becomes available.
Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
Mental Health Support
Rare disease caregiving can be isolating. Connect with counseling and peer support.
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.Is the uniparental disomy maternal or paternal, and what does that mean for my child?,What specific genes on chromosome 20 are affected by the imprinting?,Does my child need calcium and vitamin D monitoring?,Should we consider growth hormone therapy?,What developmental therapies would benefit my child?,What is the chance of this happening again in a future pregnancy?,Are there any specialists or centers with experience in this condition?
Common questions about OBSOLETE: Uniparental disomy of chromosome 20
What is OBSOLETE: Uniparental disomy of chromosome 20?
Uniparental disomy of chromosome 20 (UPD 20) is a very rare genetic condition in which a child receives both copies of chromosome 20 from one parent instead of one copy from each parent. This entry is labeled 'OBSOLETE' in Orphanet, meaning it has been retired or reclassified, often because the condition has been merged into a broader or more specific category. However, the underlying concept remains clinically relevant. When both copies of chromosome 20 come from the mother (maternal UPD 20), the most recognized consequence is Pseudohypoparathyroidism type 1B, which affects how the body respo
How is OBSOLETE: Uniparental disomy of chromosome 20 inherited?
OBSOLETE: Uniparental disomy of chromosome 20 follows a sporadic inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.