Perhaps most interestingly, the R165C mutation results in close to normal frataxin levels,17, 18, 27 yet it and other mutations with similar predicted effects (165+5 G>C, R165P) in both our and prior studies are associated with consistently atypical and especially unusual phenotypes11, 12; spared features as noted above, but with profound visual loss and diabetes early on in the disease course. This evidence concerns the gene FXN and diabetes mellitus.