EXT2 and hamartoma: As both solitary and multiple osteochondromas have been linked to loss-of-function mutations in EXT1 or EXT2 genes encoding exostosin-1 and exostosin-2 glycosyltransferase, respectively [5, 6], it was recently concluded that an osteochondroma should be considered a unique form of benign bone tumor rather than a hamartoma [6].