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FLNB gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

FLNB gene

The FLNB gene provides instructions for making filamin B, a protein essential for the development of the skeleton and the structural integrity of cells.

Normal Function

The FLNB gene provides instructions for making the protein filamin B. This protein helps build the cytoskeleton, which gives structure to cells and allows them to change shape and move. Filamin B binds to actin to form the branching network of filaments that makes up the cytoskeleton and links actin to other proteins to facilitate cell signaling.

Filamin B is crucial for skeletal development before birth. It is active in cartilage-forming cells called chondrocytes. It supports the normal growth, division, and maturation of these cells, as well as the process of ossification, where cartilage is converted into bone.

Health Conditions Related to Genetic Changes

Skeletal development disorders

Mutations in the FLNB gene are associated with several disorders that affect bone development throughout the body:

  • Atelosteogenesis type 1 and type 3: Caused by mutations that result in an abnormal protein with an atypical function that interferes with chondrocyte proliferation or differentiation.
  • Boomerang dysplasia: A severe disorder caused by mutations that impair ossification.
  • Larsen syndrome: A disorder affecting bone development, caused by mutations that interfere with normal cartilage-to-bone conversion.

It is not fully understood why similar mutations result in different disorders, though mutations in specific exons (2–5 vs. 27–33) are associated with varying levels of severity.

Spondylocarpotarsal synostosis syndrome

Mutations in the FLNB gene can cause spondylocarpotarsal synostosis syndrome. These mutations result in an abnormally short, unstable filamin B protein that breaks down rapidly. This loss of protein leads to ectopic (out-of-place) ossification, resulting in the fusion of bones in the spine, wrists, and ankles.

Other disorders

Common variations (polymorphisms) in the FLNB gene have been associated with low bone mineral density (osteoporosis), which weakens bones and increases the risk of fracture.

Genomic Location

The FLNB gene is found on chromosome 3.

Frequently Asked Questions

Most FLNB-related skeletal disorders are inherited in an autosomal dominant pattern, meaning only one copy of the altered gene is sufficient to cause the condition. However, many cases arise from de novo (new) mutations that were not present in either parent. If a parent has an FLNB-related condition, there is a 50 percent chance of passing the mutation to each child. For families with a history of severe FLNB disorders, genetic counseling and prenatal testing are recommended to assess the risk in future pregnancies.
Filamin B is essential for the structural integrity and signaling of chondrocytes, the cells responsible for forming cartilage and facilitating ossification (the process where cartilage turns into bone). In conditions like spondylocarpotarsal synostosis syndrome, mutations cause the filamin B protein to be unstable and break down rapidly. This loss of functional protein disrupts normal skeletal patterning, leading to ectopic ossification, where bone forms in areas where it should not, resulting in the fusion of adjacent bones in the spine, wrists, and ankles.
telosteogenesis is characterized by severe skeletal underdevelopment, including short limbs, abnormal bone shape, and potential respiratory complications due to a small chest cavity, often requiring intensive medical management from birth. Spondylocarpotarsal synostosis syndrome, while also caused by FLNB mutations, typically presents with a milder skeletal phenotype involving the fusion of bones in the spine, wrists, and ankles. Patients with this syndrome may experience limited joint mobility and spinal stiffness but generally do not face the immediate life-threatening respiratory issues seen in severe atelosteogenesis cases.
The position of the mutation within the gene is a critical determinant of clinical severity. Mutations occurring in exons 2 through 5 are typically associated with more severe conditions, such as atelosteogenesis type 1 or boomerang dysplasia, which often result in significant skeletal abnormalities and can be life-threatening in infancy. In contrast, mutations in exons 27 through 33 are generally linked to milder phenotypes, such as spondylocarpotarsal synostosis syndrome or certain forms of Larsen syndrome, which may present with joint stiffness and bone fusions but are usually compatible with a longer lifespan. This variation suggests that different parts of the filamin B protein play distinct roles in skeletal development.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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