ATXN1 and muscle atrophy: SCA1 is caused by a CAG repeat mutation in the Ataxin-1 (ATXN1) gene, resulting in toxic polyQ expansion that leads to a predominant loss of large populations of neurons in the cerebellum, brainstem, spinal cord, and cerebral cortex, with affected individuals experiencing pyramidal symptoms and muscle atrophy, and respiratory failure being the main cause of death (7, 16, 17).