Congenital Hypothyroidism: Causes, Consequences, and Critical Importance of Newborn Screening

Congenital hypothyroidism (CH) affects ~1 in 2,000–4,000 newborns. Thyroid hormone is essential for brain development, especially in the first 2–3 years.

Etiology

• Dysgenesis (85%): Ectopic, hypoplastic, or absent thyroid (sporadic).
• Dyshormonogenesis (15%): Enzyme defects in hormone synthesis (often autosomal recessive).
• Central (rare): Pituitary/hypothalamic failure.
• Transient: Maternal antibodies, iodine excess/deficiency, medications.

Untreated Consequences

• Irreversible intellectual disability (cretinism)
• Growth failure, delayed milestones
• Hearing loss, speech delay
• Myxedema features: coarse facies, macroglossia, umbilical hernia
• Cardiac dysfunction

Newborn Screening and Treatment

• Heel-stick TSH (or T4/TSH) at 24–48h life.
• Confirmatory serum TSH/free T4 within days.
• Levothyroxine 10–15 mcg/kg/day started immediately — goal T4 in upper half of normal by 2 weeks.
• Frequent monitoring; developmental surveillance.

Universal screening (since 1970s) has virtually eliminated intellectual disability from CH. Early treatment = normal IQ and growth.