It is also notable that among eight individuals who had been separately identified as not only having cranial neuropathies and sensorimotor neuropathy ± respiratory insufficiency but also clinical features evocative of the initial report of SLC52A2 (Johnson et al., 2012)—including sensory ataxia, predominantly upper limb and axial weakness, hearing loss and optic atrophy—all eight were found to harbour mutations in SLC52A2 (and no mutations in SLC52A1 or SLC52A3), suggesting that mutations in this riboflavin transporter gene may be quite specific to the distinct phenotype presented here. This evidence concerns the gene SLC52A2 and optic atrophy.