Overview
Absent tibia-polydactyly-arachnoid cyst syndrome is an extremely rare genetic condition that affects multiple parts of the body. The name describes its three main features: the tibia (the larger bone in the lower leg) is missing or severely underdeveloped, there are extra fingers or toes (a condition called polydactyly), and fluid-filled sacs called arachnoid cysts form on the membranes surrounding the brain and spinal cord. Because the tibia is absent or very small, children born with this condition typically have significant leg abnormalities that affect their ability to stand and walk. The extra digits may appear on the hands, feet, or both. Arachnoid cysts may or may not cause symptoms depending on their size and location, but in some cases they can lead to headaches, seizures, or developmental delays if they press on brain tissue. This syndrome is also sometimes referred to by its Orphanet designation ORPHA:3328. Because it is so rare, with only a handful of cases described in the medical literature, the treatment approach is highly individualized. Management typically involves a team of specialists and may include orthopedic surgery to address the leg and foot abnormalities, surgical removal of extra digits, and monitoring or treatment of arachnoid cysts if they cause problems. Prosthetic devices and physical therapy are often needed to help with mobility. There is currently no cure, and treatment focuses on improving function and quality of life.
Also known as:
Key symptoms:
Missing or underdeveloped shin bone (tibia)Extra fingers or toesFluid-filled cysts on the brain covering (arachnoid cysts)Shortened or bowed lower legsAbnormal foot position or shapeDifficulty walking or inability to walk without assistancePossible headaches from brain cystsPossible seizuresPossible developmental delaysLimb length differences between legs
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Neonatal
Begins at or shortly after birth (first 4 weeks)
Treatments
No FDA-approved treatments are currently listed for Absent tibia-polydactyly-arachnoid cyst syndrome.
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Specialists
View all specialists →No specialists are currently listed for Absent tibia-polydactyly-arachnoid cyst 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 Absent tibia-polydactyly-arachnoid cyst syndrome.
Community
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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 current size and location of the arachnoid cyst, and how often should it be monitored?,What are the best surgical options for my child's leg abnormalities, and when should surgery be done?,Should we pursue genetic testing such as whole exome sequencing to look for the underlying cause?,What is the recurrence risk if we plan to have more children?,What physical therapy and rehabilitation services should we start, and how often?,Are there any signs or symptoms I should watch for that would require emergency care?,Can you connect us with other families or support groups for children with limb differences?
Common questions about Absent tibia-polydactyly-arachnoid cyst syndrome
What is Absent tibia-polydactyly-arachnoid cyst syndrome?
Absent tibia-polydactyly-arachnoid cyst syndrome is an extremely rare genetic condition that affects multiple parts of the body. The name describes its three main features: the tibia (the larger bone in the lower leg) is missing or severely underdeveloped, there are extra fingers or toes (a condition called polydactyly), and fluid-filled sacs called arachnoid cysts form on the membranes surrounding the brain and spinal cord. Because the tibia is absent or very small, children born with this condition typically have significant leg abnormalities that affect their ability to stand and walk. The
How is Absent tibia-polydactyly-arachnoid cyst syndrome inherited?
Absent tibia-polydactyly-arachnoid cyst syndrome follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.
At what age does Absent tibia-polydactyly-arachnoid cyst syndrome typically begin?
Typical onset of Absent tibia-polydactyly-arachnoid cyst syndrome is neonatal. Age of onset can vary across affected individuals.