Foreword

Thyroid hormones, small iodine-containing molecules, play a key role in the growth, development, and metabolism of mammals and the metamorphosis of amphibians. The demand for iodine in hormone synthesis imposed additional stress on creatures transitioning from sea to land. Despite efforts to implement iodine supplementation, 35% of the world population remains iodine deficient today, with 35 million severely affected individuals. A significant proportion exhibits enlarged thyroid glands (goiter) and experiences growth and mental retardation. Furthermore, thyroid hormone deficiency affects one in every 2,500 newborns in iodine-sufficient areas. Timely correction of thyroid hormone deficiency induces catch-up growth, while delays in treatment result in irreversible defects in brain development. This has led to the global implementation of routine newborn screening for early detection of congenital hypothyroidism.

The book titled “Thyroid and Brain: Understanding the Actions of Thyroid Hormones in Brain Development and Function”, is authored by a preeminent expert who has devoted his entire career to the study of thyroid hormone action in the brain, thus gaining the respect of his peers for his extensive knowledge of the field. The book covers in-depth brain development, structure, and function as related to the thyroid. It provides timely, up-to-date information that will serve as a valuable resource to both specialists and non-experts. The intricate actions of these hormones are lucidly described, creating a narrative that reads almost like a novel, with each fact leading to new information, expanding the horizons of current knowledge.

The fourteen chapters delve into thyroid hormone transport, metabolism, and action as they pertain to the brain, encompassing the spectrum of thyroid hormone effects in health and disease. The book provides detailed descriptions of molecules regulating thyroid hormone action on the brain, including gene expression, properties, biochemistry, localization, and physiology. Recent advances in genetics and molecular biology are presented. While central regulation of thyroid hormone secretion involving the hypothalamus and pituitary is important, in situ thyroid hormone metabolism provides appropriate local hormone bioactivity. It ensures optimal concentrations of the biologically active thyroid hormone, T3, to brain cells as required for the particular period of development. These mechanisms regulate thyroid hormone action with a timeline specific to different brain regions. Although the book focuses on the human brain, it presents animal studies, particularly in rodents, as vital for expanding knowledge on the subject. This research reveals that gene dependence of T3 is age and brain region-dependent, with diverse time window sensitivity. T3 regulates genes involved in nearly all aspects of brain function, from developmental genes to genes involved in metabolic and cell signaling pathways. Finally, the author includes a historical overview of each topic, giving due credit for important key discoveries.