TNFRSF11B and juvenile Paget disease: Most cases of JPD are caused by osteoprotegerin (OPG) deficiency due to homozygous loss-of-function mutations within the tumour necrosis factor receptor superfamily member 11b gene (TNFRSF11B; OMIM #602643) that encodes for OPG, located on 8q24.12 [72].