Intellectual development at age 12 years of children with congenital hypothyroidism diagnosed by neonatal screening.

Twenty-seven patients with congenital hypothyroidism diagnosed by neonatal screening were examined at the age of 12 years. The 12 patients with severe hypothyroidism at diagnosis (thyroxine < 2 micrograms/dl (< 26 nmol/L), and area-of-the-knee epiphyses < 0.05 cm2 had a lower IQ than the 15 patients with less severe hypothyroidism (mean +/- SD, 89 +/- 17 vs 104 +/- 10; p < 0.007). Comparisons of patients and siblings confirm that this difference was due to the severity of hypothyroidism.