This is supplemented by testing for the two genes in which pathogenic variants are known to cause HMO namely EXT1 and EXT2. A combination of sequence analysis and deletion analysis of the entire coding regions of both EXT1 and EXT2 detects pathogenic variants in 70%-95% of affected individuals.[1][2] The hallmark of radiographic diagnosis is the presence of osteochondromas at the metaphyseal ends of long bones in which the cortex and medulla of the osteochondroma represent a continuous extension of the host bone. This is readily demonstrable in radiographs of the knees.[3][3]