Data presented at the British Endocrinology Society conference in Liverpool yesterday was said to show that newborn screening could boost intelligence among children.
UK researchers examined genetic data and thyroid function in over 3,000 seven-year old children from the Avon Longitudinal Study of Parents and Children (ALSPAC).
They found that about 4% of the children tested had both a common variant in the DIO2 (deiodinase 2) gene
along with low levels of thyroid hormone, and these children were four times more likely to have a low IQ (below 85; an average IQ is 100).
However, no impact on IQ was observed in children with either low thyroid levels alone or the genetic variant alone.
The DIO2 gene specifies an enzyme called type II iodothyronine deiodinase that activates thyroid hormone. The researchers suggest that the common variant in this gene variant may impair normal processing of thyroid hormone and reduce levels of active thyroid hormone within brain cells.
Newborn screening in the UK includes testing to identify babies with the rare genetic disorder congenital hypothyroidism, severely impaired thyroid hormone production that if left untreated can cause severe learning disability. The researchers behind this study suggest that additionally identifying children with the common DIO2 variant to receive thyroid supplementation could prevent a much milder but still significant reduction in intelligence levels.
Dr Peter Taylor of Cardiff University said: "If other studies confirm our finding then there may be benefit in carrying out a genetic test for this gene variant in addition to the standard neonatal thyroid screening, which would identify children most at risk of developing low IQ".