Neurodevelopment in infants and preschool children with congenital hypothyroidism: etiological and treatment factors affecting outcome.

Studied global intelligence and specific abilities of children from 1 to 5 years old, 108 with congenital hypothyroidism (CH) diagnosed by newborn screening and 71 sibling controls. Intelligence levels of the CH group were within the normal range but differed significantly from controls at age 5. CH demonstrated a language deficit at age 3, which diminished with age, as well as significantly poorer visuospatial and verbal skills at age 5. Children with absent thyroid glands or evidence of hypothyroidism in utero were outperformed by other CH children in most ability areas from 1 year on. Different components of ability were correlated with specific factors reflecting timing or duration of thyroid hormone deficiency, suggesting unique critical periods of thyroid hormone sensitivity for different specific cognitive abilities and their neural substrates. It is concluded that even though screened CH children are markedly improved by neonatal diagnosis, they are still at risk for subtle irreversible deficits, which depend on factors such as type, age at onset, and duration of disease.