Prognostic factors of intellectual development at 7 years of age in children with congenital hypothyroidism

The influence of the initial L-T4 dose and some other factors on the intellectual development was evaluated at 7 years of age in 47 congenitally hypothyroid children detected by the regional screening program. All patients were initially treated with 25 μg LT4/kg/day that represented a mean replacement dose of 6.8±1.3 μg/kg. Despite the “low” initial dose mean IQ at 7 years resulted within normal range (96±9). Twenty-eight patients initially treated with 6.0±0.6 μg L-T4/kg/day had a mean IQ (96±9) which was not different with respect to 19 patients (IQ 94±7) treated with a significantly higher L-T4 dose (8.1 ±0.9 μg/kg/day; p<0.0001). The initial L-T4, dose did not correlate with IQ at 7 years whereas a significant correlation was found between IQ and serum T4 concentration at diagnosis (r=0.35; p<0.01 ) regardless of the fact that serum T4 concentration normalized after the first 2 months of therapy in both groups. Twenty-three patients whose serum T4 at diagnosis was <2 μg/dl (1.0±0.5) had a mean IQ at 7 years (92±9) which was significantly lower than the 24 patients (IQ 98±7; p<0.02) whose serum T4 was >2 μg/dl (5.7±2.4; p<0.001).The present findings suggest that the severity of neonatal hypothyroidism is an important factor in determining subsequent intellectual development of congenitally hypothyroid children.