In the north of England, 23% of adults with mitochondrial disease had known or presumed nuclear genetic causes for their mitochondrial disease, with the most prevalent being mutations in SPG7 (Pfeffer et al, 2015), closely followed by PEO1 and OPA1 (Yu‐Wai‐Man et al, 2010a; Gorman et al, 2015c). This evidence concerns the gene TWNK and inborn mitochondrial metabolism disorder.