DDIT3 and amyotrophic lateral sclerosis: Interestingly, a high expression level of UPR-related markers like sXBP1, p-eIF2α, GRP78/BiP, and CHOP are also detected in the skeletal muscle of SOD1G93A mice, suggesting that the UPR pathway may be implicated in the muscle atrophy and weakness observed in ALS by affecting muscle cells instead of direct effects on motor neurons and motor pathways [176].