Currently, two main subtypes of WS are known: Wolfram syndrome type 1 (WS1), caused by the mutation of the wolframine gene (WS1; 606201)—a transmembrane protein localized in the endoplasmic reticulum whose deficiency causes increased cellular stress and apoptosis, and Wolfram syndrome type 2 (WS2), caused by the mutation of the CDGSH iron-sulfur domain-containing protein 2 gene (CISD2 gene) (WS2; 604928) and first described in a Jordanian family [6]. Here, CISD2 is linked to Wolfram syndrome 2.