IgA nephropathy (nuh-FROP-uh-thee), also known as Berger's disease, is a kidney disease that occurs when an antibody called immunoglobulin A (IgA) builds up in your kidneys. This results in local inflammation that, over time, can hamper your kidneys' ability to filter waste from your blood. Our kidneys are two bean-shaped, fist-sized organs situated at the small of your back, one on each side of your spine. Each kidney contains tiny blood vessels that filter waste, excess water and other substances from your blood as they pass through your kidneys. The filtered blood renters your bloodstream, while the waste material passes into your bladder and out of your body when you urinate. Immunoglobulin A (IgA) is an antibody that plays a key role in your immune system by attacking invading pathogens and fighting infections. But in IgA nephropathy, this antibody collects in the glomeruli, causing inflammation (glomerulonephritis) and gradually affecting their filtering ability.