Scientists have discovered a gene which increases the risk of a child having low IQ. The finding means a genetic test soon after birth could identify babies with the problem – and even paves the way for a treatment to tackle the issue. Children under seven with a common gene variant are four times as likely to develop an exceptionally low IQ if they also have reduced levels of thyroid hormone, scientists found. Some 4 per cent of all babies are born each year with the gene plus low thyroid levels. Giving children thyroid hormone tablets may allow their brains, and IQ, to develop normally, which could help 30,000 children a year. The new research focused on the deiodonase-2 enzyme, which is involved in processing thyroid hormones within cells. A mutation in the gene coding for the enzyme had already been associated with other health problems including diabetes and high blood pressure. In the new study, scientists from the universities of Cardiff and Bristol looked at genetic data on 3,123 children under the age of seven who also had their IQ tested.
Those with low levels of the thyroid hormone, and also possessed the deiodonase-2 variant, were four times more likely to have an IQ under 85 – an exceptionally low score. Children with lower thyroid hormone levels alone were not at greater risk of low IQ. 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. ‘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.’ The findings were presented at the Society for Endocrinology’s British Endocrine Societies conference in Liverpool.