Not true about congenital hypothyroidism: March 2009

Ans. A: Males more often affected Congenital Hypothyroidism (CH) is one of the most common preventable causes of mental retardation with a worldwide incidence of 1:4000 live bihs. It is usually sporadic with a 2:1 female to male preponderance. Thyroid dysgenesis is the commonest cause of permanent CH (80-85%). Thyroid hormone synthetic defects account for 10% of all cases. These are inherited as autosomal recessive disorders. The defect can lie in iodide trapping or organification, iodotyrosine coupling or deiodination and thyroglobulin synthesis or secretion. The commonest of these is a defect in the thyroid peroxidase (TPO) activity leading to impaired oxidation and organification of iodide to iodine. These disorders usually result in goitrous hypothyroidism. Majority of infants appear normal at bih. Ideally universal screening at 3-4 days of age should be done for detecting CH. Abnormal values on screening (T4 < 6.5 ug/dL, TSH >20mu/L) should be confirmed by a venous sample before initiating treatment. Term as well as preterm infants with low T4 and elevated TSH should be staed on L-thyroxine at a dose of 10-15ig/ kg/ day as soon as the diagnosis is made. Regular monitoring should be done to ensure that T4 is in the upper half of normal range. The outcome of CH depends on the time of initiation of therapy and the dose of L-thyroxine used'