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The thyroid transcription factor 1 (TTF-1) is a homeodomain-containing transcription factor that activates the transcriptional activity of thyroid-specific gene promoters by binding to them. Hence, TTF-1 is crucial in the maintenance of the thyroid differentiation phenotype (1). Thyroid dysgenesis (TD) is responsible for most cases of congenital hypothyroidism, a condition that affects about one in 4000 newborns. Mutations in PAX8, TTF1, or FOXE1 may account for congenital hypothyroidism in patients with either isolated TD or TD with associated malformations involving kidney, lung, forebrain, and palate (2). In addition to its presence in thyroid gland epithelium, the human TTF-1 protein was detected by immunohistochemistry in human fetal lung as early as 11 weeks of gestation, being localized in the nuclei of epithelial cells of the developing airways. After birth, TTF-1 was selectively expressed in Type II epithelial cells in the alveoli and in subsets of bronchiolar epithelial cells in the conducting regions of the lung (3).