PROJECT SUMMARY / ABSTRACT The biology of ALS is difficult to study, in part because of a paucity of suitable tools, and in part because of the relatively late stage in the course of the disease when the diagnosis is made. In this supplement to the parent U54 award that supports the Clinical Research in ALS and Related Disorders for Therapeutic Development, (CReATe) Consortium, we propose an analytic plan that will help to address both of these issues. Here we introduce whole-brain proton magnetic resonance spectroscopic imaging (1H MRSI) as an innovative tool to shed light on the biochemical (neurometabolite) changes in the brain associated with ALS within the context of Pre-Symptomatic Familial ALS (Pre-fALS), a longitudinal natural history, and biomarker study of individuals at genetic risk for ALS. Pre-fALS has been ongoing for ~15 years, with ~20 individuals phenoconverting to clinically manifest ALS. In a subset of these individuals, we have been able to collect multi-modal brain MRI data both before and following phenoconversion. This valuable resource offers a unique opportunity to explore the early biochemical changes in the brains of patients with ALS, with potential relevance to the future development of diagnostic biomarkers. Project-3 of our parent U54 award proposed to characterize the anatomic distribution and temporal course of structural and functional changes in pre-symptomatic C9ORF72 and SOD1 mutation carriers using structural, diffusion, perfusion, and resting-state functional MRI but did not include whole-brain proton magnetic resonance spectroscopy data. This supplemental application aims to fill this gap, with an exclusive focus on the analysis of whole-brain MRS data. Utilizing already collected MRSI data from the Pre-fALS study, this supplement will allow us to characterize the anatomic distribution of neurometabolite changes in the brains of pre-symptomatic SOD1 and C9ORF72 mutation carriers (Aim 1a). Additionally, through the planned pseudo- longitudinal analysis we aim to identify temporal patterns of changes in neurodegeneration by studying changes in metabolites in pre-symptomatic carriers across advancing age (Aim 1b). Finally, an exploratory longitudinal study in phenoconvertors will allow mapping changes in brain metabolites that could provide insights into neurodegenerative patterns that lead to ALS (Aim 2). The evaluation of MRSI data acquired as part Pre-fALS will generate for the first time detailed whole-brain maps of neurodegeneration in pre-symptomatic individuals with the potential to identify early MRSI biomarkers that might have future diagnostic utility. This supplement, which does not entail any new MRI data collection given its relatively short timeframe (12 months), will strengthen the nascent collaboration between Michael Benatar, MD, PhD (neurologist), and Mohammed Goryawala, PhD (radiologist), who is new to the field of ALS. The knowledge gained through this supplement will enable improved neurom...