Spondylocarpotarsal synostosis syndrome is a disorder that affects the development of bones throughout the body. Newborns with this disorder are of approximately normal length, but impaired growth of the torso results in short stature over time. The bones of the spine (vertebrae) are misshapen and abnormally joined together (fused). The vertebral abnormalities may result in an abnormally curved lower back (lordosis) and a spine that curves to the side (scoliosis).

People with spondylocarpotarsal synostosis syndrome have abnormalities and fusion of the bones of the wrist (carpal bones) and ankle (tarsal bones). They may also have inward- and upward-turning feet (clubfeet). Characteristic facial features include a round face, a large forehead (frontal bossing), and nostrils that open to the front rather than downward (anteverted nares).

Some people with spondylocarpotarsal synostosis syndrome have an opening in the roof of the mouth (a cleft palate), hearing loss, thin tooth enamel, flat feet, or an unusually large range of joint movement (hypermobility). Individuals with this disorder can survive into adulthood. Intelligence is generally unaffected, although mild developmental delay has been reported in some affected individuals.

Spondylocarpotarsal synostosis syndrome is a rare disorder; its prevalence is unknown. At least 25 affected individuals have been identified.

Mutations in the FLNB gene cause spondylocarpotarsal synostosis syndrome. The FLNB gene provides instructions for making a protein called filamin B. This protein helps build the network of protein filaments (cytoskeleton) that gives structure to cells and allows them to change shape and move. Filamin B attaches (binds) to another protein called actin and helps the actin to form the branching network of filaments that makes up the cytoskeleton. It also links actin to many other proteins to perform various functions within the cell, including the cell signaling that helps determine how the cytoskeleton will change as tissues grow and take shape during development.

Filamin B is especially important in the development of the skeleton before birth. It is active (expressed) in the cell membranes of cartilage-forming cells (chondrocytes). Cartilage is a tough, flexible tissue that makes up much of the skeleton during early development. Most cartilage is later converted to bone (a process called ossification), except for the cartilage that continues to cover and protect the ends of bones and is present in the nose, airways (trachea and bronchi), and external ears. Filamin B appears to be important for normal cell growth and division (proliferation) and maturation (differentiation) of chondrocytes and for the ossification of cartilage.

FLNB gene mutations that cause spondylocarpotarsal synostosis syndrome result in the production of an abnormally short filamin B protein that is unstable and breaks down rapidly. Loss of the filamin B protein appears to result in out-of-place (ectopic) ossification, resulting in fusion of the bones in the spine, wrists, and ankles and other signs and symptoms of spondylocarpotarsal synostosis syndrome.

A few individuals who have been diagnosed with spondylocarpotarsal synostosis syndrome do not have mutations in the FLNB gene. Researchers are working to identify and confirm additional genetic changes that can cause this disorder.

Genetic Testing Information

• Genetic Testing Registry: Spondylocarpotarsal synostosis syndrome

Genetic and Rare Diseases Information Center

• Spondylocarpotarsal synostosis

Patient Support and Advocacy Resources

• National Organization for Rare Disorders (NORD)

Catalog of Genes and Diseases from OMIM

• SPONDYLOCARPOTARSAL SYNOSTOSIS SYNDROME; SCT

Scientific Articles on PubMed

• PubMed

• Carapito R, Goldenberg A, Paul N, Pichot A, David A, Hamel A, Dumant-Forest C, Leroux J, Ory B, Isidor B, Bahram S. Protein-altering MYH3 variants are associated with a spectrum of phenotypes extending to spondylocarpotarsal synostosis syndrome. Eur J Hum Genet. 2016 Dec;24(12):1746-1751. doi: 10.1038/ejhg.2016.84. Epub 2016 Jul 6. Citation on PubMed or Free article on PubMed Central
• Isidor B, Cormier-Daire V, Le Merrer M, Lefrancois T, Hamel A, Le Caignec C, David A, Jacquemont S. Autosomal dominant spondylocarpotarsal synostosis syndrome: phenotypic homogeneity and genetic heterogeneity. Am J Med Genet A. 2008 Jun 15;146A(12):1593-7. doi: 10.1002/ajmg.a.32217. Citation on PubMed
• Krakow D, Robertson SP, King LM, Morgan T, Sebald ET, Bertolotto C, Wachsmann-Hogiu S, Acuna D, Shapiro SS, Takafuta T, Aftimos S, Kim CA, Firth H, Steiner CE, Cormier-Daire V, Superti-Furga A, Bonafe L, Graham JM Jr, Grix A, Bacino CA, Allanson J, Bialer MG, Lachman RS, Rimoin DL, Cohn DH. Mutations in the gene encoding filamin B disrupt vertebral segmentation, joint formation and skeletogenesis. Nat Genet. 2004 Apr;36(4):405-10. doi: 10.1038/ng1319. Epub 2004 Feb 29. Citation on PubMed
• Sawyer GM, Clark AR, Robertson SP, Sutherland-Smith AJ. Disease-associated substitutions in the filamin B actin binding domain confer enhanced actin binding affinity in the absence of major structural disturbance: Insights from the crystal structures of filamin B actin binding domains. J Mol Biol. 2009 Jul 31;390(5):1030-47. doi: 10.1016/j.jmb.2009.06.009. Epub 2009 Jun 6. Citation on PubMed
• Yang CF, Wang CH, Siong H'ng W, Chang CP, Lin WD, Chen YT, Wu JY, Tsai FJ. Filamin B Loss-of-Function Mutation in Dimerization Domain Causes Autosomal-Recessive Spondylocarpotarsal Synostosis Syndrome with Rib Anomalies. Hum Mutat. 2017 May;38(5):540-547. doi: 10.1002/humu.23186. Epub 2017 Feb 27. Citation on PubMed