Cardiac amyloidosis. Heart from a person affected by primary systemic amyloidosis. Amyloidosis is characterised by a build-up of the protein amyloid. Primary systemic amyloidosis, or amyloid light-chain (AL) amyloidosis, is caused by malfunctioning antibody-producing cells that produce abnormal protein fibres (light chains), which clump together to form amyloid deposits in the body's organs. There is no cure for amyloidosis, but the production of amyloid in the body can be slowed down by certain medications.