Compared with the natural history of treatment-naïve patients with MCT8 deficiency, body weight-for-age improved (> 0.25 SD increase compared with the natural history reference) in 32 (57%) of 55 patients upon treatment and remained stable (−0.25 to 0.25 SD change compared with the natural history reference) in 11 (20%) of 55 patients (Fig. 1E). The gene discussed is SLC16A2; the disease is hyperinsulinemic hypoglycemia, familial, 4.