Children with lower thyroid hormone levels and a particular gene variant are four times more likely to have a low IQ, research from Cardiff University’s School of Medicine has suggested. Genetic testing could be the key to optimising the cognitive development of these children.
Thyroid hormones have been established as essential for both regulation of metabolism in the body and for child brain development. Research presented at the latest Society for Endocrinology annual conference found that children with low thyroid hormone levels, coupled with possessing a certain variant of a hormone-controlling enzyme, are at risk of being less intelligent.
The enzyme deoiodinase-2 is involved in the activation of thyroid hormones within the body’s cells, and the Thr92Ala substitution of this enzyme is linked to lower levels of active thyroid hormone in the body. An occurrence of both is found in 4% of the population. This variant has previously been associated with other health issues including diabetes and high blood pressure.
Researchers from Cardiff University and the University of Bristol have studied effects of this enzyme substitution in more detail, examining genetic data, thyroid function and IQ test results of over 3000 children. The data was collected from the Avon Longitudinal Study of Parents and Children, a birth cohort that has collected information on mothers and their families since the early 1990s.
The group found not only that children with lower thyroid hormone levels and the enzyme substitution were at risk of an IQ below 85, but also that those with lower hormone levels alone were not at risk. This highlights that the genetic variant appears to modify the effects of low thyroid hormone levels on IQ.
Current standard screening of babies already checks thyroid hormone levels to identify other conditions. But, following this study, lead researcher Dr Peter Taylor of the Institute of Molecular and Experimental Medicine has said, “If other studies confirm our finding then there may be a benefit in carrying out a genetic test for this variant in addition to the standard neonatal thyroid screening, which would identify children most at risk of developing low IQ.”
Not only would genetic testing identify those at risk, it could mean that thyroid hormone treatments could aid these children in brain development. Dr Taylor added, “Children with satisfactory thyroid hormone levels together with the genetic variant have normal IQ level, which raises the possibility that children at risk could be treated with standard thyroid hormone tablets to compensate for impaired thyroid hormone processing.”