Final answer:
Transient hypothyroidism in newborns can result from diseases of the thyroid or pituitary, autoimmune diseases like Hashimoto's thyroiditis, or, most commonly worldwide, from iodine deficiency, leading to conditions like cretinism with cognitive impairment, stunted growth, and deafness.
Step-by-step explanation:
Transient hypothyroidism in the newborn can be caused by a number of factors, including diseases affecting the function of the thyroid gland or pituitary/hypothalamus, autoimmune disorders such as Hashimoto's thyroiditis, or dietary iodine deficiency. In newborns, iodine deficiency is a common cause worldwide, resulting in a condition known as cretinism, characterised by cognitive deficits, short stature, and potentially deafness and muteness. This arises when insufficient thyroid hormones, T3 and T4, are synthesized due to a lack of iodine, leading to increased thyroid-stimulating hormone (TSH) and thyroid gland size, also known as a goiter.
Within developed regions where dietary iodine is typically sufficient due to the addition of iodine to salt, hypothyroidism more commonly results from autoimmune diseases like Hashimoto's thyroiditis. Affected individuals may develop a series of adverse symptoms and related autoimmune diseases. The negative feedback loop involved in thyroid hormone release that results in thyroid hyperstimulation and goiter formation due to dietary iodine deficiency is an essential concept to understand.