Early onset and severe clinical course associated with the m.5540G>A mutation in MT-TW

•We report the second patient harboring a de novo m.5540G>A mutation.•This mutation affects the mitochondrial tryptophan-transfer RNA gene.•She presented with progressive encephalopathy with sensorineural hearing loss.•Our case had a more severe phenotype than the first reported patient.

We report a patient harboring a de novo m.5540G>A mutation affecting the MT-TW gene coding for the mitochondrial tryptophan-transfer RNA. This patient presented with atonic–myoclonic epilepsy, bilateral sensorineural hearing loss, ataxia, motor regression, ptosis, and pigmentary retinopathy. Our proband had an earlier onset and more severe phenotype than the first reported patient harboring the same mutation. We discuss her clinical presentation and compare it with the only previously published case.