SPP1 and Autoimmunity: Moreover, inactivating mutations in the ACP5 gene (encoding TRAP) cause the rare recessive disorder spondyloenchondrodysplasia, which includes autoimmunity disease features, e.g., systemic lupus erythematosus [45], associated with disturbed bone development and short stature probably mediated by impaired dephosphorylation of OPN [46, 47].