Atypical cases of osteopetrosis have been reported in two siblings affected by severe combined immunodeficiency (SCID), who carry a mutation in the TNF receptor-associated factor 6 (TRAF6) gene, the most important adaptor for the RANK/RANKL signaling pathway (Weisz Hubshman et al., 2017). The gene discussed is TNFSF11; the disease is osteopetrosis.