In a case of cardiomyopathy due to amyloidosis, what is the most likely precursor of the proteinaceous deposits?

In cases of cardiomyopathy caused by amyloidosis, the most likely precursor of the proteinaceous deposits is lambda light chains. Amyloidosis refers to the abnormal accumulation of amyloid proteins in tissues and organs, which can lead to their dysfunction. There are various types of amyloidosis, but in the case of primary (AL) amyloidosis, which is associated with hematologic conditions such as multiple myeloma, the amyloid deposits are primarily composed of light chains produced by neoplastic plasma cells.

Lambda light chains are one of the two types of immunoglobulin light chains (the other being kappa). When plasma cells proliferate abnormally, they can produce an excess of these light chains, which misfold and aggregate, forming amyloid fibrils that deposit in cardiac tissue. This accumulation disrupts normal myocardial function, leading to the characteristic symptoms and complications of amyloid cardiomyopathy.

Other choices provided, such as atrial natriuretic factor, beta-2 microglobulin, and serum amyloid A, represent different proteins associated with other types of amyloidosis or different pathophysiological processes. For instance, serum amyloid A is usually associated with secondary amyloidosis (AA), while beta-2