Thyroid gland development is coordinated by the expression of several developmental transcription factors. Thyroid transcription factor (TTF)-1 TTF-2 Paired homeobox-8 (PAX-8) are expressed selectively in the thyroid gland. They dictate thyroid cell development and the induction of thyroid-specific genes such as Thyroglobulin (Tg) Thyroid peroxidase (TPO) Sodium iodide sympoer (Na+/I, NIS) Thyroid-stimulating hormone receptor (TSH-R). Sodium iodide sympoer (Na+/I, NIS) is a thyroid specific gene and not a transcription factor. Mutations in these developmental transcription factors or their downstream target genes are rare causes of thyroid agenesis or dyshormonogenesis. Ref: Harrison, E-18, P-2912