Even with the limitation indicated immediately above, the intermediate state VSD structure can be used in conjunction with the cryo-EM structure of KCNQ1 (Sun and MacKinnon, 2017) and with available models for both resting and fully activated human KCNQ1 (Kuenze et al., 2019) to illuminate KCNQ1 pharmacology, physiology, and how some of the dozens of known LQTS disease mutations located in the VSD result in channel loss of function or dysfunction (Tobelaim et al., 2017; Huang et al., 2018; Vanoye et al., 2018). The gene discussed is KCNQ1; the disease is familial long QT syndrome.