Transaxial sections showed compact haversian structure in the control sample (healthy male, 14 yr old, fracture) (Figure 3L), whereas the size of haversian canals and resorption cavities was significantly increased in the cortical bones from type XV OI patients (Figure 3M and N), suggesting that WNT1 variants exerted deleterious effects on the bone geometry. The gene discussed is WNT1; the disease is osteogenesis imperfecta.