Human osteoclast-poor osteopetrosis with hypogammaglobulinemia due to TNFRSF11A (RANK) mutations.
Guerrini M.M., Sobacchi C., Cassani B., Abinun M., Kilic S.S., Pangrazio A., Moratto D., Mazzolari E., Clayton-Smith J., Orchard P., Coxon F.P., Helfrich M.H., Crockett J.C., Mellis D., Vellodi A., Tezcan I., Notarangelo L.D., Rogers M.J., Vezzoni P., Villa A., Frattini A.
Autosomal-Recessive Osteopetrosis (ARO) comprises a heterogeneous group of bone diseases for which mutations in five genes are known as causative. Most ARO are classified as osteoclast-rich, but recently a subset of osteoclast-poor ARO has been recognized as due to a defect in TNFSF11 (also called RANKL or TRANCE, coding for the RANKL protein), a master gene driving osteoclast differentiation along the RANKL-RANK axis. RANKL and RANK (coded for by the TNFRSF11A gene) also play a role in the immune system, which raises the possibility that defects in this pathway might cause osteopetrosis with immunodeficiency. From a large series of ARO patients we selected a Turkish consanguineous family with two siblings affected by ARO and hypogammaglobulinemia with no defects in known osteopetrosis genes. Sequencing of genes involved in the RANKL downstream pathway identified a homozygous mutation in the TNFRSF11A gene in both siblings. Their monocytes failed to differentiate in vitro into osteoclasts upon exposure to M-CSF and RANKL, in keeping with an osteoclast-intrinsic defect. Immunological analysis showed that their hypogammaglobulinemia was associated with impairment in immunoglobulin-secreting B cells. Investigation of other patients revealed a defect in both TNFRSF11A alleles in six additional, unrelated families. Our results indicate that TNFRSF11A mutations can cause a clinical condition in which severe ARO is associated with an immunoglobulin-production defect.