Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease with a complex genetic architecture, showing monogenic, oligogenic, and polygenic inheritance. In this study, we describe the case of a 71 years-old man diagnosed with ALS with an atypical phenotype, due to the presence of a progressive ocular ptosis. Genetic analyses revealed two variants in SOD1 and TBK1 genes respectively and the LHON-associated m.14484T>C variant in the mitochondrial DNA (mtDNA). We discuss how all these variants may synergically impinge on mitochondrial function, contributing to the pathogenic mechanisms which might ultimately lead to the neurodegenerative process, possibly influencing the clinical ALS phenotype.