C9orf72 and amyotrophic lateral sclerosis: In addition to the observation of no difference in expression in the dorsal horn neurons (acting as an internal control), previous findings of an upregulation of the GRIA1 transcript in ventral spinal MNs from the same C9orf72-ALS cases [40, 92] suggest that the observed down-regulation of mitochondrial gene expression in ventral horn spinal motor neurons is not due to a non-specific post-mortem artifact.