Thyroid hypoplasia

Thyroid hypoplasia (also known as thyroid gland hypoplasia) is a congenital condition in which the thyroid gland is abnormally small or underdeveloped, resulting in reduced production of thyroid hormones (hypothyroidism). It is classified as a form of thyroid dysgenesis, a group of developmental abnormalities of the thyroid gland that collectively represent the most common cause of congenital hypothyroidism. The thyroid gland, located in the front of the neck, produces hormones (T3 and T4) that are essential for normal growth, brain development, and metabolism. In affected individuals, the underdeveloped thyroid gland cannot produce sufficient thyroid hormones, leading to congenital hypothyroidism. If untreated, this can cause severe intellectual disability, growth failure, delayed skeletal maturation, constipation, feeding difficulties, prolonged neonatal jaundice, hypotonia (decreased muscle tone), a large fontanelle, macroglossia (enlarged tongue), dry skin, and lethargy. The condition primarily affects the endocrine system but has widespread consequences on the nervous system, musculoskeletal system, and overall metabolism due to the critical role of thyroid hormones in development. Thyroid hypoplasia is typically detected through newborn screening programs that measure thyroid-stimulating hormone (TSH) and/or T4 levels. Diagnosis is confirmed by thyroid ultrasound or scintigraphy, which reveals a small but normally located thyroid gland. Treatment consists of lifelong thyroid hormone replacement therapy with levothyroxine (synthetic T4), which should be initiated as early as possible — ideally within the first two weeks of life — to prevent irreversible neurodevelopmental damage. With early diagnosis and appropriate treatment, children with thyroid hypoplasia can achieve normal growth and cognitive development. Some cases are associated with mutations in genes involved in thyroid development, including PAX8, NKX2-1 (TITF1), FOXE1, and TSH receptor (TSHR) genes, though many cases are sporadic with no identifiable genetic cause.

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