(1) Deposition in tissues of an amyloidlike protein resembling light chains of immunoglobulins in primary amyloidosis or (particularly) in atypical amyloidosis of multiple myeloma. (2) Various hereditary amyloidoses (Portuguese amyloidosis, Indiana amyloidosis) characterized by progressive hypertrophic polyneuritis with sensory changes, ataxia, paresis, and muscle atrophy due to amyloid deposits in peripheral and visceral nerves.