IgA nephropathy (IgAN), also known as Berger's disease () (and variations), or synpharyngitic glomerulonephritis, is a disease of the kidney (or nephropathy) and the immune system; specifically it is a form of glomerulonephritis or an inflammation of the glomeruli of the kidney. Aggressive Berger's disease (a rarer form of the disease) can attack other major organs, such as the liver, skin and heart. IgA nephropathy is the most common glomerulonephritis worldwide; the global incidence is 2.5/100 000 a year amongst adults. Aggressive Berger's disease is on the NORD list of rare diseases. Primary IgA nephropathy is characterized by deposition of the IgA antibody in the glomerulus. There are other diseases associated with glomerular IgA deposits, the most common being IgA vasculitis (formerly known as Henoch–Schönlein purpura [HSP]), which is considered by many to be a systemic form of IgA nephropathy. IgA vasculitis presents with a characteristic purpuric skin rash, arthritis, and abdominal pain, and occurs more commonly in children. HSP is associated with a more benign prognosis than IgA nephropathy. In non-aggressive IgA nephropathy there is traditionally a slow progression to chronic kidney failure in 25–30% of cases during a period of 20 years. Signs and symptoms The classic presentation for the non-aggressive form (in 40–50% of the cases) is episodic hematuria, which usually starts within a day or two of a non-specific upper respiratory tract infection (hence synpharyngitic), as opposed to post-streptococcal glomerulonephritis, which occurs some time (weeks) after initial infection. With both aggressive and non-aggressive Berger's disease loin pain can also occur. The gross hematuria may resolve after a few days, though microscopic hematuria will persist, it is however more common with aggressive Berger's disease for gross hematuria to persist rather than microscopic hematuria. Renal function usually remains normal with non-aggressive Berger's disease, though rarely acute kidney failure may occur (see below). This presentation is more common in younger adults. A smaller proportion (20–30%), usually the older population, have microscopic hematuria and proteinuria (less than 2 gram/day). These patients may be asymptomatic and only picked up due to urinalysis. Hence, the disease is more commonly diagnosed in situations where screening of urine is compulsory (e.g., schoolchildren in Japan). Very rarely (5% each), the presenting history is: Nephritic syndrome Acute kidney failure (either as a complication of the frank hematuria, when it usually recovers or due to rapidly progressive glomerulonephritis which often leads to chronic kidney failure) Chronic kidney