OPA3 and Behr syndrome: Mutations affecting OPA1, a dynamin-related guanosine triphosphatase involved in mitochondrial dynamics, represent a major cause of dominant OA (DOA), and ∼20% of patients may present a DOA “plus” phenotype, including axonal neuropathy.25 Biallelic mutations in OPA1 can also cause Behr syndrome,26, –, 28 a severe, early-onset neuro-ophthalmologic syndrome that is clinically similar to MGA3.