The most frequently mutated gene in these patients was DUOX2, followed by TG, TPO, DUOXA1, DUOX1 and TSHR. Mutations were identified in 9 of 15 mutated genes involved in thyroid hormone synthesis (DUOX2, TG, TPO, DUOXA1, DUOXA2, DUOX1, TSHR, SLC26A4 and IYD) in 87 (79.1%, 87/110) patients and 57 of these patients (51.82%, 57/110) carried biallelic mutations in DUOX2, TG, TPO, TSHR, DUOXA2 and DUOXA1. In contrast, eight patients harbored heterozygous mutations in NKX2-1, FOXE1, PAX8 or HHEX, which lead to thyroid dysgenesis. This evidence concerns the gene HHEX and hypothyroidism, congenital, nongoitrous, 2.