A newborn male is diagnosed with congenital hypothyroidism on newborn screening. If levothyroxine replacement therapy is delayed or omitted during the first months of life, what is the most significant permanent adverse consequence?

Answer and explanation

Correct answer: A. Permanent neurocognitive impairment and intellectual disability (cretinism)

  1. Step 1: Thyroid hormone is essential for neonatal brain development, neurogenesis, and myelinogenesis during the critical early post-natal window.
  2. Step 2: Untreated congenital hypothyroidism leads to permanent, irreversible cognitive impairment, psychomotor delay, and stunted skeletal growth (cretinism). Prompt levothyroxine initiation within the first 2 weeks prevents intellectual deficit.
Answer
Permanent neurocognitive impairment and intellectual disability (cretinism).
Why not the others: 'Hearing loss only' underestimates the severe global central nervous system consequences; 'Craniosynostosis' is premature suture fusion associated with hyperthyroidism, not hypothyroidism; 'Type 1 diabetes' is an autoimmune islet disease unrelated to neonatal T4 deficiency.

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