The progress of ALS research and clinical practice is hampered by lack of effective biomarkers to monitor disease onset and progression. In response to this urgent need, we will integrate single-cell system biology approaches, histopathological and clinical data from precious human nerve biopsies collected from living ALS patients during the diagnostic workup and findings from innovative preclinical mouse models to unmask cell-specific molecular alterations that arise in the PNS tissue during the course of ALS pathology. This information will be used to select protein biomarkers of dysfunctional states associated with pre-manifest or early symptomatic stages of the disease, which will be further screened and validated in patient biofluids. Altogether, this project will lead to the discovery of novel, reliable and specific ALS biomarkers while providing insights into ALS mechanisms by leveraging an original "PNS perspective" on disease pathogenesis.