PAX-8 is a protein which in humans is encoded by the PAX8 gene. The PAX gene family has an important role in the formation of tissues and organs during embryonic development and maintaining the normal function of some cells after birth.This nuclear protein is involved in thyroid follicular cell development and expression of thyroid-specific genes. PAX8 releases the hormones important for regulating growth, brain development, and metabolism. Also functions in very early stages of kidney organogenesis, the müllerian system, and the thymus.The PAX8 gene is also associated congenital hypothyroidism due to thyroid dysgenesis because of its role in growth and development of the thyroid gland. A mutation in the PAX8 gene could prevent or disrupt normal development.