Skip to content
Skip to navigation menu


Genetic screening could identify children at risk of low IQ development

24 March 2014

Children with both a common gene variant and lower thyroid hormone levels, which occurs in approximately 4% of the population, are four times more likely to have a low IQ, according to research presented today by Cardiff University at the Society for Endocrinology annual BES conference.

It is well established that thyroid hormones are essential for brain development in childhood. More recently, scientists have looked at a certain enzyme, called deiodonase-2, involved in processing thyroid hormones inside cells. A variant in the gene coding this enzyme has already been associated with key health outcomes including diabetes and high blood pressure, although the precise mechanism remains unclear.

In this study, researchers from Cardiff University and the University of Bristol examined the genetic data and thyroid function of 3,123 children aged 7 who also had their IQ tested, as part of the Avon Longitudinal Study of Parents and Children (ALSPAC). The researchers found that children with thyroid hormone levels in the lower part of the normal population range who also possessed this genetic variant were four times more likely to have an IQ under 85. 

This result stood true after taking into account various differences in environmental and socio-economic factors such as social class. Children with lower thyroid hormone levels alone did not have an increased risk of lower IQ, highlighting that without genetic analysis the population at risk could not be identified. 

The study’s results will need to be confirmed in other groups of children. "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," said lead researcher Dr Peter Taylor, from Cardiff University’s School of Medicine. "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," he added.



Useful links:

Dr Peter Taylor

Notes to Editors:


Thyroid hormone is essential for childhood development. Genetic variation might predispose individuals with low-normal thyroid hormone levels to adverse cognitive outcomes.

We explored whether individuals with low thyroid hormone bioavailability (defined as free thyroxine in the lowest quartile in combination with homozygote status at the Thr92Ala substitution in deiodonase-2) had higher odds of lower IQ scores.

Cohort Study

Population-based birth cohort, the Avon Longitudinal Study of Parents and Children

2,996 individuals with genetic data, thyroid function (age 7) and cognitive assessments (age 8).

Main Outcome Measures
Odds of having an IQ score <85 in children with low thyroid hormone bioavailability Analyses were adjusted for age, sex, thyroid hormone parameters and early life environment.

Children with low thyroid hormone bioavailability had higher odds of an IQ<85 (OR=2.36 95%CI 1.24, 4.49 p=0.009), and an IQ <80 (OR=4.03, 95%CI 1.83, 8.88 p=0.001) and lower mean IQ (p=0.007) compared to those with normal thyroid hormone bioavailability. We also observed evidence of interaction between free thyroxine in the lowest quartile and the Thr92Ala substitution in their relationship with IQ (p=0.008). There was no evidence of association with IQ in individuals with just free thyroxine in the lowest quartile, or with just the Thr92Ala substitution.

Common genetic variation in the intracellular thyroid hormone pathway appears to substantially modify the effect of low-normal serum thyroid hormone levels on IQ. Further studies are needed to assess if targeted thyroid hormone replacement in a genotype dependent manner may improve clinical outcomes.

*The introduction to ‘The Thr92Ala substitution in deiodonase-2 is associated with increased odds of a sub-optimal IQ score in children when in combination with low-normal thyroid function’ paper can be issued on request.

For further information please contact:

Tomas Llewelyn Barrett
Public Relations 
Cardiff University 
Tel: 029 20 875 596 
Mobile: 07950792532

Cardiff University

Cardiff University is recognised in independent government assessments as one of Britain’s leading teaching and research universities and is a member of the Russell Group of the UK’s most research intensive universities.  Among its academic staff are two Nobel Laureates, including the winner of the 2007 Nobel Prize for Medicine, University Chancellor Professor Sir Martin Evans.  Founded by Royal Charter in 1883, today the University combines impressive modern facilities and a dynamic approach to teaching and research. The University’s breadth of expertise encompasses: the College of Arts, Humanities and Social Sciences; the College of Biomedical and Life Sciences; and the College of Physical Sciences, along with a longstanding commitment to lifelong learning. Cardiff's four flagship Research Institutes are offering radical new approaches to cancer stem cells, catalysis, neurosciences and mental health and sustainable places.