TANGO2 and hyperinsulinemic hypoglycemia, familial, 4: This is not the first case report to describe this phenotypic presentation in a patient who was ultimately diagnosed with TANGO2 deficiency, and this is the second reported case found on genetic screening after an initial diagnosis and management of suspected LQTS.2 However, a unique factor in our case is that our patient responded well to β-blocker therapy alone for a period of 8 years prior to the eventual diagnosis of TANGO2 deficiency, at which time management specific to this mutation was implemented.