Ischiopatellar dysplasia

Ischiopatellar dysplasia is a rare autosomal dominant disorder characterized by hypoplasia of the patellae along with other bone anomalies, especially of the pelvis and feet. It is also called small patella syndrome, and older names include Scott-Taor syndrome and coxo-podo-patellar syndrome. The kneecaps are typically absent or small, and when present they are small and displaced sideways. Other reported features include delayed or absent ossification of the ischium, flat feet, syndactyly of the toes, short fourth and fifth toes, cleft palate and facial differences, and complications can include recurrent dislocation, knee pain and late-onset arthritis of the knee, although some people have no symptoms. Mutations in the TBX4 gene on chromosome 17, which is important for lower limb development, have been found to cause it. Diagnosis rests on radiography and genetic testing, and about fifty to seventy cases are described in the literature. Scott and Taor recognized it as a family disorder in 1979, distinct from the more severe nail-patella syndrome.