Spondylocarpotarsal synostosis

Spondylocarpotarsal synostosis syndrome (SCT syndrome), also known as spondylocarpotarsal synostosis or congenital scoliosis with unilateral unsegmented bar, is a rare skeletal disorder characterized by the fusion (synostosis) of the vertebrae (spondylo-), carpal (wrist), and tarsal (ankle) bones. The condition primarily affects the skeletal system, leading to progressive vertebral fusions that result in a short trunk and disproportionate short stature. Vertebral block fusions, particularly involving the thoracic and lumbar spine, are a hallmark feature and can produce a characteristic unilateral unsegmented bar appearance on imaging. Additional skeletal findings include lordosis, scoliosis, and fusions of the carpal and tarsal bones. Affected individuals may also exhibit facial dysmorphism, including a broad nasal bridge and a round face, as well as dental anomalies and mild hearing loss in some cases. The condition is caused by biallelic pathogenic variants in the FLNB gene (filamin B), which encodes a cytoskeletal protein important for vertebral segmentation and skeletal development. The FLNB gene is also associated with other skeletal dysplasias, including Larsen syndrome and atelosteogenesis types I and III, though those conditions follow different inheritance patterns. Spondylocarpotarsal synostosis syndrome follows an autosomal recessive inheritance pattern. Onset is typically recognized in childhood, often when short stature or spinal abnormalities become clinically apparent, though vertebral fusions may be present from birth. There is currently no cure for spondylocarpotarsal synostosis syndrome. Management is supportive and multidisciplinary, focusing on orthopedic monitoring and intervention for progressive spinal deformities, which may include bracing or surgical correction in severe cases. Respiratory function should be monitored, as restrictive lung disease can develop secondary to thoracic vertebral fusions. Hearing assessments and dental evaluations are also recommended. Genetic counseling is important for affected families to understand recurrence risks.

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