RMND1 and mitochondrial DNA depletion syndrome, encephalomyopathic form with methylmalonic aciduria: The clinical phenotypes associated with RMND1 mutations are expanding, ranging from a fatal, infantile encephalomyopathy with lactic acidosis2, 5 to a less severe phenotype characterised by developmental delay, congenital sensorineural deafness, hypotonia and renal disease.4, 6 In this study, we identified new patients harbouring recessive mutations in RMND1 from several metabolic clinics and research centres across Europe (UK, Ireland, Italy, Denmark, Spain and Czech Republic) and the USA.