Hereditary multiple osteochondromas (HMO) is an autosomal dominant bone disorder that presents as multiple benign cartilage-capped tumors. The major morbigenous genes EXT1 and EXT2 account for 90% of HMO cases. In HMO patients, osteochondromas appear adjacent to the physis and remain in the metaphyseal lesion of the long bones. Consequently, it is uncommon for osteochondromas to form a bone bridge in the inferior tibiofibular syndesmosis. We present a rare case of a 20-year-old female patient

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... th HMO with limited flexing range in her left ankle joint. Based on plain radiographs, a bone bridge formed by osteochondromas was situated in the distal tib-iofibular syndesmosis of her left ankle. A novel nonsense mutation, c.67C>T p.Arg23X in exon 2 of the EXT2 gene, was discovered; we inferred that this mutation was the cause of HMO.