ABSTRACT
Dual oxidase maturation factor 2 (DUOXA2) is necessary for the enzymatic activity of dual oxidase 2 (DUOX2) to generate hydrogen peroxide production during thyroid hormone synthesis. We describe two Korean children, who were initially suspected to have transient congenital hypothyroidism (CH), but later confirmed to have permanent CH caused by DUOXA2 mutation. Treatment with levothyroxine was discontinued after confirming thyroid-stimulating hormone (TSH) level to be below 10 μU/mL and normal thyroid scan at the first or second trial-off therapy. However, after therapy cessation, TSH elevated to more than 10 μU/mL, and goiter developed in case 2. As a result, levothyroxine was resumed. Next-generation sequencing showed compound heterozygous mutations of DUOXA2 at Y138X and Y246X in case 1 and homozygous mutations of DUOXA2 at Y246X in case 2. In this report, a longer follow-up is recommended even after treatment termination in transient CH, and genetic studies might help assess the permanence of hypothyroidism in cases of mildly elevated TSH after trial-off therapy.