The last hypothesis about σ2 receptors identity has been proposed by Alon and colleagues in 2017, when the σ2 receptor was identified as the TMEM97 (also known as MAC-30), an ER resident protein involved in cholesterol homeostasis [41] and in the Niemann–Pick type C disease as NPC1-interacting protein [42]. Here, TMEM97 is linked to Niemann-Pick disease type C.