FBXL4 and mitochondrial DNA depletion syndrome 13: In humans, pathogenic, bi‐allelic FBXL4 variants result in encephalopathic mitochondrial DNA (mtDNA) depletion syndrome (MTDPS13) (Bonnen et al, 2013; Gai et al, 2013; Ballout et al, 2019), a multi‐system disease that presents with congenital lactic acidosis, neurodevelopmental delays, poor growth and encephalopathy (Bonnen et al, 2013; Gai et al, 2013).