Congenital hypothyroidism: age at start of treatment versus outcome.

We studied 27 patients with congenital hypothyroidism by neurological and psychometric methods. 7 healthy siblings served as a control group for the psychometric evaluation. In 7 patients treatment had been started before the age of 1 month and in 10 patients after the age of 3 months. Our findings suggest that the progressive loss of intelligence potential starts from birth but if treatment is begun before the age of 1 month, then intelligence remains within normal range. The neurological damage seems to originate partly before birth, but more serious injuries arise if treatment is delayed beyond the age of 3 months.