Anatomical Associations Between Focal Mitochondrial Metabolism and Patterns of Neurodegeneration in Amyotrophic Lateral Sclerosis

Objective Amyotrophic lateral sclerosis (ALS) has a very specific neuroimaging signature, but the molecular underpinnings of the strikingly selective anatomic involvement have not elucidated to date. Accordingly, a large neuroimaging study was conducted with 258 participants to evaluate associations between patterns of neurodegeneration and focal metabolic metrics. Methods Structural and diffusivity alterations were systematically evaluated in a genetically stratified cohort. Voxelwise associations between neurodegeneration and physiological mitochondrial indices were systematically evaluated over the entire brain and also examined in specific regions. Results Significant topological associations were identified between physiological mitochondria tissue density, nicotinamide adenine dinucleotide (NADH)–ubiquinone oxidoreductase, succinate dehydrogenase, cytochrome c oxidase (COX), mitochondrial respiratory capacity (MRC), tissue respiratory capacity (TRC), and propensity to focal atrophy in ALS. Anatomic correlations between mitochondrial metrics and morphometric change were particularly strong in GGGGCC hexanucleotide repeat carriers in C9orf72 . Diffusivity analyses also confirmed associations between brain metabolism and microstructural degeneration. Higher focal mitochondria tissue density was associated with higher likelihood of frontal, temporal, cerebellar, opercular, thalamic, cingulum, putamen, corpus callosum, and corona radiata degeneration. Uncinate fasciculus degeneration was associated with higher Complex I, II, COX, and TRC activity. Topological associations were readily replicated in an external validation cohort. Interpretation Our data indicate that brain regions with high metabolic activity are particularly vulnerable to neurodegeneration in ALS. Anatomic associations between physiological cerebral metabolism and patterns of neurodegeneration implicate mitochondrial dysfunction in the pathophysiology of ALS. Although mitochondrial dysfunction may not be the primary etiological factor, it may represent a shared bottleneck of multiple converging molecular and genetic pathways, offering a potential opportunity for meaningful pharmacological intervention.