Children With Congenital Hypothyroidism and Their Siblings: Do They Really Differ?
© 2005 Prime Health Consultants, Inc.
In this paper, Rovet demonstrates her extensive experience with the serial evaluation of the intelligence of patients with congenital hypothyroidism (CH); 42 full-term, otherwise healthy, patients were identified in the newborn screening program, and were compared with their 42 normal siblings at ages 6 years to 9 years. The use of siblings as a control group diminishes the genetic and socioeconomic factors that may affect intelligence testing. The children were examined (albeit in differing calendar years) with either the McCarthy Scales of Children’s Abilities (at age 6 years, n=19 pairs) or Wechsler Intelligence Scale for Children-Revised (WISC-R) (at age 7 or 9 years, n=30 pairs). The Intelligence Quotient (IQ) measured by either the McCarthy (general cognitive index) or Wechsler (full scale IQ) revealed no difference between test instruments. At comparable ages, between 6 years and 9 years, children with CH had lower mean IQ scores than did their siblings: McCarthy: CH 106.5 Siblings 114.6 Δ -8.1 points; WISC-R: CH 102.7 Siblings 108.9 Δ -6.8 points. Subjects with CH due to agenesis or dysgenesis of the thyroid gland had lower IQ scores than their siblings, but patients with CH due to dyshormonogenesis did not. In the CH subjects, there was no relationship between IQ and bone age, serum thyroxine concentration at diagnosis, or age of initiation of therapy (12 or 13 days), but children who received higher starting doses of thyroxine (8.2 μg/kg/d) had a higher IQ score than did those children who received a lower starting dose of thyroxine. Indeed, the mean IQ of the high-dose thyroxine children was 109.3 points, comparable to that of the sibling group. Rovet concluded that children with CH may not attain their target IQ despite early intervention, and that a high initial dose of thyroxine may help overcome this deficit.
Editor’s Comment: Although many of the findings of this investigation have been observed in earlier studies, this report is unique in the comparison of IQ scores between siblings with/without CH at comparable ages tested with identical instruments by a single observer. Nevertheless, several of the analyses may be limited by a still relatively small sample size. For instance, by statistical evaluation, bone age at the initiation of treatment for CH did not affect measured IQ at 6 to 9 years; however, the mean IQ of children with CH and bone ages at 36 weeks was -8.4 points lower than subjects with CH and bone ages of 37 to 40 weeks. In other reports, bone age, initial thyroxine concentration, age at initiation of treatment, and starting dose of thyroxine have been related to developmental outcome.
Allen W. Root, MD
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