Skeletal Muscle Biomarkers of Amyotrophic Lateral Sclerosis: A Large‐Scale, Multi‐Cohort Proteomic Study

Objective Biomarkers with clear contexts of use are important tools for amyotrophic lateral sclerosis (ALS) therapy development. Understanding their longitudinal trajectory in the untreated state is key to their use as potential markers of pharmacodynamic response. To this end, we undertook a large‐scale proteomic study in well‐phenotyped cohorts to identify biomarker candidates of ALS disease state and disease progression. Methods Clinical phenotypic data and biofluid samples, collected from patients with ALS and healthy controls through multiple longitudinal natural history studies, were used to identify biomarker candidates. Slow off‐rate modified aptamer (SOMAmer)‐based relatively quantitative measurement of ~7,000 proteins was performed in plasma and cerebrospinal fluid (CSF), with immunoassay validation of candidates of interest. Results We identified 329 plasma proteins significantly differentially regulated between ALS and controls (adjusted p ‐value 40% relative abundance. PDLIM3, TNNT2, and MYL11 had the greatest log‐fold elevation, whereas ANTXR2 and ART3 had the greatest log‐fold reduction. A similar set of plasma proteins was found to increase (eg, PDLIM3, TNNT2, and MYL11) or decrease (eg, ANTXR2, ART3, and MSTN) with disease progression. CSF proteins with the greatest log‐fold elevation included NEFL, NEFH, CHIT1, CA3, MYL11, and GPNMB. These results were confirmed in an independent replication cohort. Moreover, tissue‐specific signature enrichment suggests a significant contribution of muscle as a source of these biomarkers. Plasma KCNIP3 was elevated by ~60% in those on riluzole. Immunoassays provided orthogonal validation of plasma TNNT2 and CSF GPNMB. Interpretation We identified an array of novel biomarkers with the potential to serve as response biomarkers to aid therapy development, as well as to shed light on the underlying biology of disease. ANN NEUROL 2025