Primary congenital hypothyroidism

Primary congenital hypothyroidism (CH) is a condition present at birth in which the thyroid gland fails to produce adequate amounts of thyroid hormones, most commonly thyroxine (T4) and triiodothyronine (T3). It is one of the most common preventable causes of intellectual disability worldwide. The condition may result from thyroid dysgenesis (absent, ectopic, or hypoplastic thyroid gland), which accounts for approximately 80-85% of cases, or from thyroid dyshormonogenesis (defects in thyroid hormone synthesis), which accounts for most of the remaining cases. In rare instances, it can also be caused by defects in TSH receptor signaling. Thyroid hormones are essential for normal growth and neurodevelopment, particularly during the first years of life. Without early detection and treatment, affected infants may develop severe and irreversible intellectual disability, growth failure, and neurological impairment. In the neonatal period, symptoms can be subtle but may include prolonged jaundice, feeding difficulties, constipation, a large fontanelle, hypotonia (decreased muscle tone), macroglossia (enlarged tongue), umbilical hernia, dry skin, hoarse cry, and lethargy. Many affected newborns appear clinically normal at birth, which underscores the critical importance of newborn screening programs. Newborn screening for congenital hypothyroidism, now implemented in most developed countries, allows early diagnosis typically within the first two weeks of life. Treatment consists of lifelong thyroid hormone replacement therapy with levothyroxine (synthetic T4), which should be initiated as soon as possible after diagnosis — ideally within the first two weeks of life. With prompt and adequate treatment, children with primary congenital hypothyroidism can achieve normal or near-normal cognitive development and growth. Regular monitoring of thyroid function tests is essential to ensure appropriate dosing throughout childhood and into adulthood.

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