Amyloid Typing in Cardiac Amyloidosis Using Western Blotting

Background: Cardiac amyloidosis (CA) is characterized by the extracellular deposition of misfolded protein in the heart. Precise identification of the amyloid type is often challenging, but critical, since the treatment and prognosis depend on the disease form and the type of deposited amyloid. Coexistence of clinical conditions such as old age, monoclonal gammopathy, chronic inflammation, or peripheral neuropathy in a patient with cardiomyopathy creates a differential diagnosis between the major types of CA: light chain amyloidosis (AL), transthyretin amyloidosis (ATTR) and amyloidosis A (AA). Objectives: To demonstrate the utility of the Western blotting (WB)-based amyloid typing method in patients diagnosed with cardiac amyloidosis where the type of amyloid was not obvious based on the clinical context. Methods: Congo red positive endomyocardial biopsy specimens were studied in patients where the type of amyloid was uncertain. Amyloid proteins were extracted and identified by WB. Mass spectrometry (MS) of the electrophoretically resolved protein-in-gel bands was used for confirmation of WB data. Results: WB analysis allowed differentiation between AL, AA, and ATTR in cardiac biopsies based on specific immunoreactivity of the electrophoretically separated proteins and their characteristic molecular weight. The obtained results were confirmed by MS. Conclusions: WB-based amyloid typing method is cheaper and more readily available than the complex and expensive gold standard techniques such as MS analysis or immunoelectron microscopy. Notably, it is more sensitive and specific than the commonly used immunohistochemical techniques and may provide an accessible diagnostic service to patients with amyloidosis in Israel.