Larsen syndrome is a result of mutations of the FLNB gene. This gene is responsible for creating the filamin B protein, which is crucial for the cell to create a network of structural proteins known as the cytoskeleton. The cytoskeleton plays an important role in the structure, flexibility, and motility of the cell.

Classic history and presentation: Presentation of Larsen syndrome is widely variable. Common features in newborns include dislocations in the elbows, knees, and/or hips. Clubfoot is commonly seen in young children with Larsen syndrome. Other notable features include scoliosis, short stature, hyperflexible joints, extraneous small bones within the ankle and wrist, and fingertips that are square and blunt, along with certain facial features such as frontal bossing, midface hypoplasia, and cleft palate.

Prevalence: Larsen syndrome follows an autosomal dominant pattern of inheritance. The prevalence is around 1 per 100 000 newborn children. Typically, this is an autosomal dominant condition with a mutation to the FLNB gene. Although rare, Larsen syndrome may be inherited as an autosomal recessive disorder or be caused by mutation in the LAR1 gene at 3p21.1-142.

Risk factors:

• Family history of Larsen syndrome
• Parent with low-level mosaicism

Pathophysiology: Mutations within the FLNB gene alter production of filamin B, leading to disruption of the cellular cytoskeleton and collagen.