To date, changes in the T3/T4 ratio have only been described in a few cases and in small cohorts, e.g., in patients with hyper- and hypothyroidism, in children with MCT8 deficiency [19], in children with congenital hypothyroidism treated with L-thyroxine, and in relation to iodine status in children [20,21,22], but no normal values have been reported. Here, SLC16A2 is linked to congenital hypothyroidism.