We have described 18 patients with mutations in the riboflavin transporter gene SLC52A2 who demonstrate a striking clinical phenotype of sensory ataxia and upper limb, axial and respiratory weakness as a result of an axonal sensorimotor peripheral neuropathy; and a cranial neuropathy affecting cranial nerves II (optic atrophy), VIII (hearing loss) and XII (tongue fasciculations ± tongue weakness and atrophy). The gene discussed is SLC52A2; the disease is Leber hereditary optic neuropathy.