Overview
Synpolydactyly type 1 (also called SPD1 or syndactyly type II) is a rare inherited condition that affects the development of the fingers and toes before birth. In this condition, a person is born with extra fingers or toes (polydactyly) combined with webbing or fusion between certain fingers or toes (syndactyly). The most common pattern involves webbing between the third and fourth fingers of the hand, with an extra finger partially hidden within the webbed skin. In the feet, webbing typically occurs between the fourth and fifth toes, sometimes with an extra toe present as well. The severity can vary widely, even among members of the same family — some people may have very mild webbing that is barely noticeable, while others may have more complex hand or foot differences that affect function. Synpolydactyly type 1 is caused by changes (mutations) in the HOXD13 gene, which plays an important role in limb development during pregnancy. The condition follows an autosomal dominant inheritance pattern, meaning only one copy of the altered gene is needed to cause the condition. Treatment is primarily surgical and focuses on separating fused fingers or toes and removing extra digits to improve hand and foot function and appearance. With appropriate surgical care, most individuals with synpolydactyly type 1 lead fully normal and active lives. Early evaluation by a hand surgeon or orthopedic specialist experienced in limb differences is recommended to plan the best timing and approach for any needed procedures.
Key symptoms:
Webbing or fusion between the third and fourth fingersExtra finger hidden within the webbed skin of the handWebbing or fusion between the fourth and fifth toesExtra toe in the footShortened or unusually shaped fingers or toesStiffness in affected fingers or toesUneven finger or toe lengthDifferences in hand or foot appearance between left and right sidesMild difficulty with fine motor tasks if fingers are fusedNail abnormalities on affected digits
Autosomal dominant
Passed on from just one parent; each child has about a 50% chance of inheriting it
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for Synpolydactyly type 1.
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Specialists
View all specialists →No specialists are currently listed for Synpolydactyly type 1.
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 Synpolydactyly type 1.
Community
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Caregiver Resources
NORD Caregiver Resources
Support, advocacy, and financial assistance for caregivers of rare disease patients.
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.How severe is my child's synpolydactyly, and which fingers and toes are affected?,Will my child need surgery, and if so, what is the best age to have it done?,How many surgeries might be needed, and what results can we expect?,Should we pursue genetic testing to confirm the diagnosis?,What is the chance that future children will also have this condition?,Will my child need occupational therapy after surgery?,Are there any long-term complications we should watch for as my child grows?
Common questions about Synpolydactyly type 1
What is Synpolydactyly type 1?
Synpolydactyly type 1 (also called SPD1 or syndactyly type II) is a rare inherited condition that affects the development of the fingers and toes before birth. In this condition, a person is born with extra fingers or toes (polydactyly) combined with webbing or fusion between certain fingers or toes (syndactyly). The most common pattern involves webbing between the third and fourth fingers of the hand, with an extra finger partially hidden within the webbed skin. In the feet, webbing typically occurs between the fourth and fifth toes, sometimes with an extra toe present as well. The severity c
How is Synpolydactyly type 1 inherited?
Synpolydactyly type 1 follows a autosomal dominant inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Synpolydactyly type 1 typically begin?
Typical onset of Synpolydactyly type 1 is neonatal. Age of onset can vary across affected individuals.