Similarly, mutations in the WFS1 gene lead to Wolfram syndrome, a severe neurodegenerative disorder characterized by diabetes insipidus, diabetes mellitus, optic atrophy, and deafness (DIDMOAD), caused by chronic endoplasmic reticulum (ER) stress and subsequent β-cell apoptosis [9,10]. Here, WFS1 is linked to Leber hereditary optic neuropathy.