Chapter 8 - Congenital Defects of Thyroid Hormone Synthesis

Abstract

This chapter focuses on the congenital defects in synthesis of thyroid hormone. Congenital hypothyroidism (CH) is mentioned to be the most inborn endocrine disorder and one of the most preventable causes of mental retardation. The disorder may be associated with abnormalities of thyroid gland development and migration (thyroid dysgenesis) or the disease can be caused by inherited defects in one of the steps of thyroid hormone synthesis (thyroid dyshormonogenesis). The etiological classification of CH is stated to be based on clinical and biochemical evaluation by measurement of serum thyrotropin, thyroxine, triiodothyronine and thyroglobulin by thyroid ultrasonography and scintigraphy. The identification of key steps involved in thyroid hormone synthesis can make molecular genetic diagnosis feasible for a majority of dyshormonogenesis patients. The pathophysiology and genetics of specific dyshormonogenesis defect is elaborated. An effective treatment of patients with specific defects is mentioned to be iodide supplementation rather than by levothyroxine and an early molecular diagnosis can predict the necessity for life-long hormone replacement therapy.