Finally, in line with recent findings suggesting that HA in hemophilia B may be less severe than in hemophilia A as reflected by either clinical parameters or differences in levels of TNF/TNF-R superfamily members controlling bone turnover, such as osteoprotegerin and activator of nuclear factor-kB ligand [8,26], it will be of major importance to also search for possible differences in the proinflammatory TNF-α pathway between the two types of hemophilia. Here, TNFRSF11B is linked to hemophilia A.