B-123 Clinical Implication of Light Chain Fragmentation in Patients with Monoclonal Gammopathies
Year: 2025
Type: conference-abstract
Abstract: Background The diagnosis of monoclonal gammopathies relies on the detection of monoclonal immunoglobulins (M-proteins) in serum or urine. Mass-Fix utilizes matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry (MS) to detect and quantify M-proteins. This method employs immunoaffinity enrichment using antibodies against heavy chains (HC) and light chains (LC), followed by MS analysis to determine M-protein isotypes. Mass-Fix has also revealed novel M-protein characteristics, including LC glycosylation and fragmentation, facilitated by measuring the mass of LC. LC glycosylation is as an independent risk factor for disease progression of monoclonal gammopathy of undetermined significance (MGUS), while light chain fragments have been postulated as the origin of amyloid light chain (AL) plaques. Since Mass-Fix enriches intact immunoglobulins before dissociating LCs, it potentially enhances fragment detection. However, the precise nature and clinical significance of these fragments remain to be fully elucidated. Methods Mass-Fix serum results from Mayo Clinic patients tested from September 10, 2018, to October 1, 2024, were reviewed for the presence of M-protein and LC fragments. The frequency and the isotype of fragment LC fragments was determined in the M-protein positive cohort (n=15410). Patients diagnosed with either MGUS (n=6996), AL amyloidosis (n=315), or both (n=32) who had positive M-protein results on Mass-Fix, either prior to or within one month after the diagnosis, were included for a retrospective clinical association study of LC fragments and disease. To validate that these fragments were not artifacts of MS analysis, PAGE gel analysis and Western blots were performed using clinical residual serum from 9 patients: 2 IgG/kappa and 3 IgG/lambda patients with detectable LC fragments and 2 IgG/kappa and 2 IgG/lambda patients without fragments. Samples were purified using antibodies against gamma heavy chains and reduced with TCEP prior to gel electrophoresis and Western blot. Results Of the 15410 patients with monoclonal proteins detected by Mass-Fix, 2896 (18.7%) had detectable LC fragments; kappa fragments in 1533 and lambda fragments in 1363. Most often, the fragments were observed in pairs, with combined molecular weight typically equaled that of the full-length monoclonal LC present in the same sample. LC fragments were observed more frequently among patients diagnosed with AL amyloidosis (118/347=34%) compared to those without the diagnosis (685/6996=10%), with an odds ratio of 4.75 (95% CI, 3.75-6.01). PAGE with Coomassie blue staining revealed bands with sizes representing LC fragments in the five M-protein samples with detectable LC fragments on Mass-Fix, while no such bands observed in those without LC fragments. Western blot using anti-kappa or anti-lambda antibodies confirmed the identity of the bands with higher molecular weight as a fragment of LC in each of the IgG/kappa and IgG/lambda samples. Conclusion Mass-Fix is able to discriminate LC fragments from intact LC based on their sizes. The detection of LC fragments with Western blot without ionization suggests a biological origin rather than analytical artifacts from MS. The clinical association study suggests that LC fragments may have utility in increasing the suspicion of AL amyloidosis in M-protein positive patients with LC fragments, potentially facilitating earlier intervention and improving patient outcomes.
Source: Clinical Chemistry
Authors: Jack Wu, Louisiane Courcelles, Patrick Vanderboom, Jonathan Coker, Mindy Kohlhagen, Brandon Copet, James Larkin, Surendra Dasari, Angela Dispenzieri, Maria Alice Willrich, David Murray
Institutions: Mayo Clinic, Cliniques Universitaires Saint-Luc
Language: English
Subfield: Hematology
Field: Medicine
Domain: Health Sciences
Open Access status: bronze
OpenAlex ID: W4414740948