Congenital hypothyroidism is associated with mental retardation and may be associated with decreased motor activity at birth, hoarse cry, and difficulty with feeding. It is rarely diagnosed at birth from clinical assessment alone, but it is recognized from new-born screening tests with confirmation by measurement in blood samples. Symptoms of hypothyroidism may not be clearly detected until the second month of life. The overall prevalence is 1 in 4000 live births. Neurological and learning disorders associated with untreated congenital hypothyroidism include attention-deficit disorder, hearing loss, speech defects, ataxia, and abnormal muscle tone. (35 Rapid diagnosis in infancy is essential to prevent these complications. Without treatment, severe neurological dysfunction ensues. With initiation of oral thyroid hormone treatment (levothyroxine in a single daily dose of 8 to 10 pg/kg per day) in the first 6 weeks of life, IQ is in the normal range. If treatment is delayed until 3 to 6 months, IQ drops to an average of 75, and, if initiated after 6 weeks, to an IQ of 55 or less.
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