Amyloidosis is classified as (i) primary amyloidosis and amyloidosis related to multiple myeloma (light chain amyloidosis [AL]), (ii) secondary amyloidosis (amyloid A amyloidosis [AA]), or (iii) familial amyloidosis (amyloidogenic transthyretin [ATTR]) on the basis of the chemical composition of the tumors. The gene discussed is TTR; the disease is AL amyloidosis.