Amyloid Light-chain (AL) amyloidosis, primary systemic amyloidosis (PSA) or just primary amyloidosis is the most common form of systemic amyloidosis in the US. The disease is caused when a person's antibody-producing cells do not function properly and produce abnormal protein fibers made of components of antibodies called light chains. These light chains come together to form amyloid deposits in different organs which can cause serious damage to these organs. Abnormal light chains in blood and urine are sometimes referred to as "Bence Jones protein".