Gain-of-function and loss-of-function gene variants identify a novel pathway for Mendelian lupus and lupus nephritis.

Systemic lupus erythematosus (SLE) is a chronic and inflammatory autoimmune disease of unknown origin that may cause kidney disease, i.e. lupus nephritis (LN). Within a wider trend towards an expanding field of genetic causes of kidney disease, two recent reports have emphasized the role of Mendelian autoimmune disorders in causing LN both in children and in young adults. Loss-of-function (LOF) variants of tumor necrosis factor alpha-induced protein 3 ( and gain of function (GOF) variants of Toll-like receptor 7 () cause SLE and LN, respectively. Interestingly, both genes regulate the same signaling route, as A20, the protein encoded by , inhibits nuclear factor ĸB (NF-ĸB) activation while TLR7 promoted NF-ĸB activation. Moreover, and variants are relatively frequent, potentially contributing to polygenic risk for LN. Finally, they both may be expressed by kidney cells, potentially contributing to the severity of kidney injury in persons who have already developed autoimmunity. The fact that both genes regulate the same pathway may lead to novel therapeutic approaches targeting the shared molecular pathway.