A person with amyloidosis produces abnormal protein fibers, known as amyloid, which are deposited in body tissues. Tissues include the intestines, tongue, skeletal muscle, smooth muscle, nerves, brain, skin, ligaments, heart, liver, spleen, and kidneys. The amyloid may interfere with the normal function of these organs.

Amyloidosis is most common in those between 60 and 70 years old. The illness may be mild or severe.