A novel mass spectrometry method to identify the serum monoclonal light chain component in systemic light chain amyloidosis

AL amyloidosis is characterised by an underlying plasma cell clone producing structurally abnormal monoclonal free light chains (FLCs) which mis-fold and deposit as amyloid fibrils leading to progressive tissue damage. Detection and serial measurements of serum FLCs are critical in determining prognosis and in assessing response to treatment. All current immunoassays for quantifying amyloidgenic monoclonal FLCs also measure the normal polyclonal FLC background—a major limitation for a disease where even low-level monoclonal FLCs are crucially important. We describe a novel mass spectrometry (MS) method for accurate detection of monoclonal free light chains in patients with systemic AL amyloidosis.