Research
Research done using Zebrafish dackel (dak) have shown that in EXT2-/- Zebrafish, chondrocytes fail to undergo terminal differentiation and bone formation fails to progress from pre-osteoblasts stage to osteoblasts. Instead, abnormal lipid deposition and premature adipocyte differentiation takes place. The expression of xbp1, master regulator of osterix gets reduced, suggesting that unfolded proteins responses may play a role in pathogenesis of multiple osteochondroma. The research concludes that heparan sulphates are required for terminal differentiation and formation of scaffold that is needed for bone development. At least one copy of EXT2 gene is needed for proper bone development and to maintain the balance between bone and fat cell lineages. Due to homozygous loss of EXT2 function, leads to imbalance between cartilage, bone, and fat cell lineages. These observations in null zebrafish points toward the musculoskeletal defects observed in patients with multiple osteochondroma. Due to the findings of bone-fat imbalance in Zebra fish model, future studies should address status of lipid composition in patients with multiple osteochondroma. Research conducted using sequencing methods has identified a novel frame shift mutation at the glycosyltransferase domain (c.1457insG) located at codon 486 of exon 6 of the EXT1 gene, that causes multiple osteochondromas. This study was conducted in two multiple osteochondroma (MO) patients from the Chinese descent (same family) and the results were validated with four other members of the same MO family and 200 unrelated healthy subjects. The results of the mutations were validated using two different sequencing methods (Exome and Sanger).
Osteochondromas are the most common benign tumors of the bones. The tumors take the form of cartilage-capped bony projections or outgrowth on the surface of bones exostoses. It is characterized as a type of overgrowth that can occur in any bone where cartilage forms bone. Tumors most commonly affect long bones about the knee and in the forearm. Additionally, flat bones such as the pelvis and scapula (shoulder blade) may be affected. Hereditary multiple exostoses usually present during childhood. Yet, the vast majority of affected individuals become clinically manifest by the time they reach adolescence. Osteochondromas occur in 3% of the general population and represent 35% of all benign tumors and 8% of all bone tumors. The majority of these tumors are solitary non-hereditary lesions and approximately 15% of osteochondromas occur as hereditary multiple exostoses preferably known as hereditary multiple osteochondromas (HMOs). Osteochondromas do not result from injury and the exact cause remains unknown. Recent research has indicated that multiple osteochondromas is an autosomal dominant inherited disease. Germ line mutations in EXT1 and EXT2 genes located on chromosomes 8 and 11 have been associated with the cause of the disease. The treatment choice for osteochondroma is surgical removal of solitary lesion or partial excision of the outgrowth, when symptoms cause motion limitations or nerve and blood vessel impingements. In hereditary multiple exostoses the indications of surgery are based upon multiple factors that are taken collectively, namely: patients age, tumor location and number, accompanying symptomatology, esthetic concerns, family history and underlying gene mutation.