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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.
Rovet JF. Children with congenital hypothyroidism and their siblings: Do
they really differ? Pediatrics.
2005;15:52-57; DOI: 10.1542/peds.2004-1492.
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
Reference - (linked to  )
- Simoneau-Roy J, Marti S, Deal C, Huot C, Robaey P, Van Vliet G. Pediatrics. 2004;144:747–752.
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