Background:Myoclonic epilepsy with ragged red fibers (MERRF) syndrome is characterized by myoclonus,generalized epilepsy,cerebellar ataxia,and ragged red fibers (RRFs) in the muscle.T-to-C transition at nucleotide position 14709 in the mitochondrial tRNA glutamic acid (tRNAGlu) gene has previously been associated with matally inherited diabetes and deafness.However,the association between MERRF and mitochondrial T14709C mutation (m.T14709C) has never been reported before.Methods:Clinical information of a 17-year-old patient was collected;muscle biopsy and next-generation sequencing (NGS) of whole mitochondrial and neuromuscular disease panel were then conducted.Finally,sanger sequencing was carried out to confirm the mutations.Results:The patient presented a typical MERRF phenotype with muscle weakness,epileptic seizure,clonic episodes,cerebellar ataxia,and spinal scoliosis.Muscle biopsy showed RRFs which indicated abnormal mitochondrial functions.NGS of whole mitochondrial gene revealed m.T14709C mutation,confirmed by Sanger sequencing.Conclusion:We present a sporadic patient with typical MERRF presentation carrying the mutation of m.T 14709C,which expanded the spectrum of m.T 14709C.