Membranous nephropathy (MN, also membranous glomerulonephritis) is a chronic inflammatory kidney disease. As has been known for many years, deposits in the kidney form over the course of the disease. These affect the kidney function and lead to inflammation. The exact causes remained unknown for a long time despite intensive research. It was only in 2009 and 2014 that two antibodies were found which cause the deposits in the more frequent form of the disease, primary membranous nephropathy (pMN), and consequently hinder the filtering of the blood. They are autoantibodies: antibodies which are directed against the body's own structures.
This leads to the typical symptoms of pMN:
The disease course may differ, encompassing spontaneous remission, persistent proteinuria, or even complete kidney failure.
In 2009, researchers identified the first autoantibody to play a role in the development of pMN in the blood of a pMN patient. This antibody is directed against the protein PLA2R, which occurs in the blood-urine filter in the kidney. This discovery is considered a milestone in nephrological research.
Through further research, a second autoantibody directed against a protein which occurs in the kidney (THSD7A) was discovered in 2014. It can be detected in the blood of up to 15 % of those pMN patients who do not show antibodies against PLA2R.
There are no significant differences between patients with autoantibodies against PLA2R and patients with autoantibodies against THSD7A.
Besides pMN, there is also the secondary form of MN. It is due to another underlying disease, e.g. an infection, another autoimmune disease, a tumour disease or drug intoxication. This secondary membranous nephropathy (sMN) is present in up to 20 to 30% of MN patients. No respective autoantibodies were found in these patients.
Diagnostic differentiation of primary and secondary MN is very important for the treatment. While therapy in sMN mainly focuses on the underlying disease, pMN can in most cases be treated successfully with immunosuppressives.
In some persons, no causative autoantibodies can be detected, nor does the MN have other identifiable causes. These forms of MN are referred to as idiopathic.