A disease characterised by the deposition of amyloid in various organs of the body. It is generally considered that the amyloidoses share common pathogenic mechanisms which lead to protein fibril formation and deposition. These mechanisms may include structural, metabolic, genetic and environmental factors that may be common to all forms of amyloidosis. Primary amyloidosis, while the most common form of amyloidosis, is a sporadic disease and, therefore, can only be investigated on a case by case basis. Secondary (reactive) amyloidosis occurs in subjects with chronic inflammatory disease or cancer but factors which predict amyloid formation and which subject is going to be affected, are not readily apparent. Alzheimer disease, while very common in the aged population, is unpredictable except for those rare forms of familial Alzheimer disease with characterized mutations in specific genes. Hereditary transthyretin amyloidosis has generally been considered a rare disease and the original impetus to study the pathogenesis of this disease was because it represented a human model of systemic amyloidosis.