Bilateral paediatric optic neuropathy precipitated by vitamin B12 deficiency and a novel mitochondrial DNA mutation.

We present an 11-year-old girl with sudden, severe, sequential optic neuropathy. Investigations revealed severe vitamin B12 deficiency, and identified a novel mitochondrial ND5 variant. She was treated with steroids followed by plasma exchange, but the vision continued to deteriorate to eventual bilateral blindness over the next few months. Vitamin B12 deficiency can rarely cause severe irreversible visual loss secondary to optic neuropathy. The significance of the concurrent mitochondrial ND5 variant remains undetermined.