Children could be genetically screened to find out if they will have low intelligence, scientists have claimed.
Researchers have found that children under the age of seven with a common gene variant coupled with low levels of thyroid hormone were four times more likely to have an IQ below 85.
The discovery raises the possibility that around 30,000 babies a year could be diagnosed and treated with thyroid tablets before the problem damages their education.
Lead researcher Dr Peter Taylor, from the University of Cardiff's School of Medicine, 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.
"Children with satisfactory thyroid hormone levels together with the genetic variant have normal IQ levels, which raises the possibility that children at risk could be treated with standard thyroid hormone tablets to compensate for impaired thyroid hormone processing."
Around four per cent of the population have the gene variant coupled with a lower than normal thyroid hormone levels.
The finding could mean that up to 2.5 million people in Britain could be suffering from the effects of low IQ which might have been treatable.