Moreover, many of the mouse models developed to study mutations in these ARO-associated genes display several common phenotypes that include, in addition to massive osteopetrosis, absent or under-developed RBs, an inability to acidify the OCL-bone interface, reduced or absent bone-resorbing activity, and altered OCL shape or size (e.g., Kornak et al., 2001; Rajapurohitam et al., 2001; Kasper et al., 2005; Henriksen et al., 2006; Lange et al., 2006; Neutzsky-Wulff et al., 2008; Wartosch et al., 2009; Weinert et al., 2010; Héraud et al., 2014; Pata and Vacher, 2018) (Table 2). The gene discussed is CYP19A1; the disease is osteopetrosis.