Membranous glomerulonephritis (MGN) is a slowly progressive disease of the kidney affecting mostly people between ages of 30 and 50 years, usually Caucasian.Membranous Nephropathy (MN) is a kidney disease that affects the filters (glomeruli) of the kidney and can cause protein in the urine, as well as decreased kidney function and swelling. It can sometimes be called membranous glomerulopathy as well (these terms can be used interchangeably and mean the same thing). Membranous nephropathy is one of the most common causes of the nephrotic syndrome in adults. Nephrotic syndrome includes significant amounts of protein in the urine (at least 3.5 grams per day), low blood protein (albumin) levels, and swelling (edema). Membranous nephropathy can occur by itself (primary) or due to another disease or underlying cause (secondary). This will be discussed more later, but some things that can cause secondary MN include lupus, cancer, or certain medications. This webpage will focus mostly on primary MN.Often, membranous nephropathy results from some type of autoimmune activity. Your body's immune system mistakes healthy tissue as foreign and attacks it with substances called autoantibodies. These autoantibodies target certain proteins located in the kidney's filtering systems (glomeruli). This is known as primary membranous nephropathy. Membranous nephropathy may also occur along with other kidney diseases, such as diabetic nephropathy and rapidly progressive (crescentic) glomerulonephritis.