Markers of presymptomatic amyotrophic lateral sclerosis: State of the art, practical implications and perspectives.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with an identified genetic origin in 10-15% of cases, mainly involving C9orf72 and SOD1 mutations. The increasing number of genetically confirmed ALS cases has led to a growing identification of asymptomatic mutation carriers. While riluzole remains the standard treatment, mutation-specific therapies such as tofersen, that was recently approved in SOD1-ALS, are emerging. In this context, the identification of presymptomatic biomarkers is crucial for monitoring genetically at-risk individuals. Plasma neurofilament light chain can increase up to 3.5years before symptom onset in C9orf72 carriers. Metabolic and neuroimaging alterations together with cognitive or behavioral changes, that are sometimes detectable decades prior to diagnosis, have also been observed. These biomarkers may support early surveillance and intervention strategies. The present review provides an overview of current evidence on presymptomatic biomarkers in ALS mutation carriers and their potential role in genetic counseling, monitoring, and early therapeutic decisions.