EFFECT OF THYROID-HORMONE ON GROWTH - LESSONS FROM THE SYNDROME OF RESISTANCE TO THYROID-HORMONE

Thyroid hormone deprivation results in deleterious effects on bone gro wth. Delayed bone development is mediated by a direct effect of thyroi d hormone on bone and an indirect effect of the hormone on growth horm one release and IGF-I action. Both thyroid hormone receptors alpha and beta are expressed in bone cells. To examine the role of thyroid horm one receptor beta on bone, the growth abnormalities in the human syndr ome of resistance to thyroid hormone caused by mutations in the thyroi d hormone receptor beta gene are reviewed. These mutant receptors redu ce the tissue responsiveness to thyroid hormone, producing variable de grees of thyroid hormone deprivation in some tissues. With regard to b one, relative thyroid hormone deficiency caused by the mutant thyroid hormone receptor beta produces short stature and delayed bone growth. These observations indicate that an intact thyroid hormone receptor be ta is required for normal bone development and growth.