[Prognosis of cognition in congenital hypothyroidism following early treatment. Double effect hypothesis]

The prevention of mental retardation due to congenital hypothyroidism by treating it at an early stage is one of the great achievements of contemporary preventive medicine. Nevertheless, the children suffering from this disease are affected by selective cognitive deficits whose origin remains a controversial issue.

We describe the results from a cohort of 100 children who have been diagnosed as suffering from congenital hypothyroidism in La Havana since 1989 and whose cognitive performance has since been periodically evaluated. The mean age at each evaluation was as follows: 1.1 years (mean and typical deviation: 0.3) and 8.2 years (mean and typical deviation: 1.2).

During the first two years of life the developmental quotients are within the normal range of values, although fine oculomotor coordination is significantly diminished. The duration of fetal hypothyroidism is linked to postural control, and the initial biochemical severity of the disease is associated to language development. Oculomotor coordination is not linked to any variable concerning the severity of the disease or with the effectiveness of therapy. At school age, intelligence quotients (IQ) are also within the normal range of values. A multiple regression analysis indicated that the total IQ can be predicted from the scores in oculomotor coordination during the first two years of life and from the initial doses of levothyroxine.

The relations between the variables capable of forecasting intellectual development in these children are analysed and we also discuss the hypothesis which suggests that some of the persisting neurocognitive deficits are probably due to genetic influences that exist regardless of the effectiveness of the therapy.