Notably, marker genes for both stage 1 (Fgf21, Mthfd2, and Asns) and stage 2 (Psat1 and Phghd) mitochondrial stress responses identified previously by (Forsström et al, 2019) were elevated in the IMMD model by P28 and were DELE1-dependent. Here, FGF21 is linked to autosomal dominant mitochondrial myopathy with exercise intolerance.