Congenital hypothyroidism (cretinism) in neuroD2-deficient mice.

Mice lacking neuroD2, a basic helix-loop-helix transcription factor involved in brain development, show growth retardation and other abnormalities consistent with hypothalamic-pituitary-thyroid (HPT) axis dysfunction. neuroD2 is expressed in the paraventricular hypothalamic nuclei, the anterior lobe of pituitary, and the thyroid gland. In neuroD2-deficient mice, thyrotropin-releasing hormone, thyroid-stimulating hormone, and thyroid hormone are decreased in these three regions, respectively. neuroD2-null mice typically die 2 to 3 weeks after birth, but those treated with replacement doses of thyroxine survived more than 8 weeks. These data indicate that neuroD2 is expressed throughout the HPT axis and that all levels of the axis are functionally affected by its absence in mice.