TPO and hypothyroidism, congenital, nongoitrous, 2: This is important both for GIS CH and thyroid dysgenesis because variants in genes involved in thyroid hormone biosynthesis (e.g., Pendrin, TPO, and DUOX2) have recently been implicated in thyroid dysgenesis, and mutations in morphogenesis-associated genes (e.g., FOXE1) have been implicated in GIS CH (18, 34–38).