Larsen syndrome is characterized by joint hypermobility, multiple joint dislocations, especially of the knees, and talipes equinovarus. The midface is hypoplastic with a depressed nasal bridge. Cleft palate may be present. Radiographs reveal under-mineralisation and over-tubulation of the long bones, a bifid calcaneus and advanced bone age in the carpal, or extra carpal bones. Scoliosis, coronal clefts of the vertebrae and subluxation of the vertebra may be found. Scientists emphasized the importance of differentiating Larsen syndrome from other conditions in which arthrogryposis is the presumed diagnosis. The latter is, however, a symptom complex and not a diagnosis.
Missense mutations were identified in the gene encoding filamin B (FLNB gene) in individuals with autosomal dominant Larsen syndrome. The filamins are cytoplasmic proteins that regulate the structure and activity of the cytoskeleton by cross-linking actin into three-dimensional networks, linking the cell membrane to the cytoskeleton and serving as scaffolds on which intracellular signaling and protein trafficking pathways are organized.