brachydactyly type B2

Brachydactyly type B2 is a very rare inherited difference in hand and foot development that primarily affects the bones of the fingers and toes. It is caused by changes in the NOG gene, which encodes noggin, a protein that helps regulate early bone and joint formation. Because the condition is present at birth, children are the group most often diagnosed, and males and females are affected equally. Precise prevalence figures have not been established, but published reports suggest that only a small number of families worldwide have been described. Although limb differences are the hallmark, some individuals also have hearing or vision concerns, so the condition can involve more than one body system.

The skeletal system is most consistently involved. Nearly all affected individuals have very short or absent middle and distal finger and toe bones, especially in digits four and five, leading to shortened digits and broad fingertips. The joints closest to the hand or foot are often fused (proximal symphalangism), and the wrist or ankle bones may be joined together (carpal or tarsal synostosis). Some people also have partial webbing of the skin between fingers or toes and a thumb that sits closer than usual to the wrist. Outside the skeleton, a minority experience sensorineural hearing loss, and farsightedness has been reported. Not all individuals experience all features, and severity varies considerably from one person to another, even within the same family.

Brachydactyly type B2 results from pathogenic variants in the NOG gene. Noggin acts as an antagonist of bone morphogenetic proteins, molecules that guide the growth and separation of bones during early development. When noggin does not work properly, certain bones in the hands, feet, and other areas fail to form or separate completely, leading to the physical findings described above. The condition follows an autosomal dominant inheritance pattern, meaning a change in one copy of NOG is sufficient to cause symptoms and an affected parent has a 50 percent chance of passing the variant to each child. Even within families, the exact features can differ, a phenomenon called variable expressivity. Genetic counseling is recommended for families to discuss testing of relatives, reproductive options, and expectations for variability.

Currently, management focuses on supportive care and symptom management tailored to each person’s needs. Hand or orthopedic specialists may recommend occupational or physical therapy to maximize hand function and address any joint stiffness. Reconstructive surgery can be considered for troublesome syndactyly or severe joint fusion, but the decision is individualized. Hearing and vision should be formally evaluated at diagnosis and monitored over time so that hearing aids, glasses, or other interventions can be offered promptly. Because different organ systems can be involved, long-term care is best coordinated by a multidisciplinary team. Regular surveillance helps identify emerging musculoskeletal, auditory, or visual issues early, allowing interventions to be planned at the most effective time. Families should discuss management strategies and follow-up schedules with their healthcare providers and may benefit from connecting with a genetic counselor.

Overall health and life expectancy are generally normal, and many individuals lead independent lives with adaptations for hand function as needed. Outcomes depend on the severity of bone involvement, the presence of hearing or vision problems, and access to specialized care. Early intervention, appropriate assistive devices, and thoughtful surgical planning can significantly improve functional abilities and quality of life. Severity and symptoms vary widely between individuals, even within the same family. Outcomes described in medical literature continue to evolve as standards of care improve. Families often find it helpful to connect with specialists familiar with congenital limb differences and to seek genetic counseling for guidance and support.