Overview
Radioulnar synostosis-developmental delay-hypotonia syndrome is a very rare genetic condition that affects multiple parts of the body. The hallmark feature is radioulnar synostosis, which means the two bones in the forearm (the radius and ulna) are fused together. This fusion limits the ability to rotate the forearm, making it difficult to turn the palm up or down. In addition to the bone abnormality, children with this syndrome typically have developmental delay, meaning they are slower to reach milestones like sitting, walking, and talking compared to other children their age. Hypotonia, or low muscle tone, is another key feature, which can make babies appear "floppy" and contribute to feeding difficulties and delayed motor skills. Other features that may be seen include intellectual disability of varying degrees, distinctive facial features, and sometimes additional skeletal abnormalities. Some affected individuals may also have behavioral challenges. The severity of symptoms can vary from person to person, even within the same family. There is currently no cure for this condition, and treatment focuses on managing individual symptoms through therapies such as physical therapy, occupational therapy, speech therapy, and sometimes surgical intervention for the forearm fusion if it significantly limits function. Early intervention services are important to help children reach their full developmental potential.
Also known as:
Key symptoms:
Fusion of the forearm bones (cannot rotate the forearm normally)Low muscle tone (floppiness)Delayed development of motor skills like sitting and walkingDelayed speech and language developmentIntellectual disabilityFeeding difficulties in infancyDistinctive facial featuresPoor coordinationDifficulty with fine motor tasks like writing or buttoning clothesLimited ability to turn the palm up or downBehavioral challengesShort stature in some cases
Clinical phenotype terms (20)— hover any for plain English
Variable
Can be inherited in different ways depending on the underlying gene
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for Radioulnar synostosis-developmental delay-hypotonia syndrome.
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Specialists
View all specialists →No specialists are currently listed for Radioulnar synostosis-developmental delay-hypotonia syndrome.
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 Radioulnar synostosis-developmental delay-hypotonia syndrome.
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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.What is the specific genetic cause of my child's condition, and should we pursue further genetic testing?,What therapies are most important to start right away?,Is surgery an option for the forearm fusion, and what are the risks and benefits?,What developmental milestones should I watch for, and when should I be concerned?,Are there any other medical issues we should screen for?,What educational supports and services should we request for my child?,What is the chance that future children could also be affected?
Common questions about Radioulnar synostosis-developmental delay-hypotonia syndrome
What is Radioulnar synostosis-developmental delay-hypotonia syndrome?
Radioulnar synostosis-developmental delay-hypotonia syndrome is a very rare genetic condition that affects multiple parts of the body. The hallmark feature is radioulnar synostosis, which means the two bones in the forearm (the radius and ulna) are fused together. This fusion limits the ability to rotate the forearm, making it difficult to turn the palm up or down. In addition to the bone abnormality, children with this syndrome typically have developmental delay, meaning they are slower to reach milestones like sitting, walking, and talking compared to other children their age. Hypotonia, or
At what age does Radioulnar synostosis-developmental delay-hypotonia syndrome typically begin?
Typical onset of Radioulnar synostosis-developmental delay-hypotonia syndrome is neonatal. Age of onset can vary across affected individuals.