The link between intelligence and dementia

Feb 15 2005

Scientists have turned to the brightest brains in Britain in a bid to understand the link between intelligence and dementia.

A team of researchers from The University of Manchester will be asking members of the high-IQ society Mensa for DNA samples in what will be the world's most sophisticated study of brainpower.

The research will allow the team to find genes associated with intelligence and examine how they interact with each other.

"When you look at the genes in combination you reduce the statistical power of the research considerably," explained Dr Tony Payton, who works in the University's Centre for Integrated Genomic Medical Research (CIGMR) and is leading the research.

"Selecting individuals who represent the extreme end of the IQ distribution increases this power dramatically. For example, 200 volunteers with an IQ of 145 is equivalent to using 100,000 unselected volunteers."

The results of the Mensa research will complement data collected from an earlier University of Manchester study of some 2,500 elderly people that has taken place over the last 20 years.

That research has already uncovered two genes associated with general cognitive ability, while work elsewhere over the past eight years has identified a further 10 other 'intelligence genes'.

"The study of intelligence is shrouded by historical, biological, ethical and descriptive complexities that have made a mockery of its intended definition 'to reason and understand'," said Dr Payton.

"Although our understanding of the biological basis of intelligence is still at an early stage, a general consensus about the role genes play in determining the level of intelligence has now been reached.

"All of us possess the same genes but there are variations within the genes themselves, known as 'polymorphisms', which are largely responsible for what makes us all unique.

"They have an important influence on factors such as our behaviour and susceptibility to disease and, of the genes implicated in intelligence, the associated polymorphism has been shown to alter the function of the gene."

Theoretically, the research with Mensa will be the most powerful approach to studies in this field ever adopted.

The study of 2,500 elderly people over 20 years has created the second largest DNA archive in the world – the Dyne Steele DNA bank – and is unique in that it assessed volunteers for changes in cognitive function.

"Combining this study with the Mensa research will take cognitive genetic research to an altogether new level and maintain The University of Manchester's position as a world leader in the field," said Dr Payton.

"Scientists are interested in intelligence genes because high intelligence protects against the onset of dementias such as Alzheimer's disease.

"A greater understanding of the role that genes play in regulating intelligence may help in the development of new diagnostic tests and more effective treatments designed to combat cognitive impairment in the elderly."

Mensa has more than 25,500 members in the United Kingdom and Ireland, all of whom have an IQ that is measured in the top 2% of the population.

The aim of the project is to initially recruit at least 1,000 members and investigate if there is a difference between their genetic polymorphisms and those found in average IQ individuals using the Dyne Steele DNA bank.

Most studies to date have only investigated single polymorphisms in single genes but given there are more than 33,000 human genes these approaches are incredibly expensive and time consuming.

Using cutting-edge technology, known as 'Affymetrix Microarray', Dr Payton's team will be able to investigate more than 100,000 polymorphisms at a time and hope to identify many intelligence genes in a short time.