RNASEH1 and inborn mitochondrial metabolism disorder: Immortalized fibroblasts derived from patients with mutations in RNASEH1, coding for a protein involved in mtDNA maintenance (Reyes et al, 2015) or ISCU, encoding a scaffold protein for the assembly of iron‐sulfur (Fe‐S) clusters (Legati et al, 2017) have been studied as additional cell models of mitochondrial disease in order to establish if the reported changes were unique to mutant TIMM50 fibroblasts or shared with other disease cell lines.