Thyroid-Brain Interactions in Neuropsychiatric Disorders

Thyroid hormones are important for the development and maturation of the brain as well as for the functioning of the mature brain. Most thyroid hormone responsive genes are sensitive to thyroid hormones only during distinct periods of brain development, but some are also sensitive in the mature brain. A variety of factors influence the effects of thyroid hormones in the brain: availability of iodine; thyroid diseases and dysfunction; genetic variations that affect thyroid axisrelated proteins, such as deiodinases, thyroid hormone transporters, and receptors; and timing of events. Interaction of these factors contributes to the development of the brain as well as to presentation of psychiatric symptoms and disorders in the mature brain. Clinical and subclinical thyroid dysfunction, thyroid autoimmunity, as well as individual genetic variations and mutations of thyroid axisrelated proteins, may contribute not only to the presentation of psychiatric symptoms and disorders but also to response to psychiatric treatments. Better understanding of genomic and nongenomic mechanisms related to thyroid hormone metabolism in the brain opens new venues for finding new markers, new targets, and new agents for the treatment of mental disorders.