PAX8 and hypothyroidism, congenital, nongoitrous, 2: Homozygous Pax8 knockout resulted in thyroid aplasia in mice [16] and heterozygous loss-of-function PAX8 mutations were associated with various forms of thyroid dysgenesis in humans [7, 17], genetically implicating the role of PAX8 defect in thyroid dysgenesis.