ACP5 and systemic lupus erythematosus: Although loss-of-function mutations of Acp5 cause spondyloenchon-drodysplasia with immune dysregulation (SPENCDI), which is a skeletal and neurological disorder with lupus-like symptoms and a type I interferon signature (31), the expression of Acp5 mRNA increased in patrolling monocytes in NZBWF1 mice.