SLC17A6 and Leber hereditary optic neuropathy: However, the slow progression of optic atrophy in G13997A mice impedes large-scale testing of pharmacotherapies or gene therapies in this model, with no RGC axonal loss observed at 14 months and only ~ 25% by 24 months18 (compared to 33% by P60 in Vglut2-Cre;ndufs4loxP/loxP mice).