Study links tendency to undervalue future rewards to ADHD, obesity and smoking

James MacKillop, director of the Peter Boris Centre for Addictions Research.

A McMaster University researcher is part of a team that has found a genetic signature for delay discounting — the tendency to undervalue future rewards — that overlaps with attention-deficit/hyperactivity disorder (ADHD), obesity and smoking.

James MacKillop, director of the Peter Boris Centre for Addictions Research at McMaster University and St. Joseph’s Healthcare Hamilton, is a co-investigator on the study that used data from customers of a genetic testing company, 23andMe. The customers consented to participate in research and answered survey questions to assess delay discounting.

In total, the research included more than 23,000 research participants of European ancestry. The data showed that approximately 12 percent of a person’s variation in delay discounting can be attributed to genetics — not a single gene, but numerous genetic variants that also influence several other psychiatric and behavioral traits.

The study was published in Nature Neuroscience today.

“Deficits in this form of self-control have been linked to many disorders, but genetic contributions have only been examined in small samples using a handful of variants,” said MacKillop, a professor of psychiatry and behavioural neurosciences for McMaster’s Michael G. DeGroote School of Medicine. “This study is vastly larger than previous ones and examined variation across the entire genome.”

By comparing participants’ survey responses to their corresponding genotypes and complementary data from other studies, the team under the leadership of researchers of the University of California San Diego School of Medicine, found a number of genetic correlations.

One correlation was between ADHD and delay discounting. The study does not suggest everyone with ADHD will undervalue future rewards, but rather that the two factors have a common underlying genetic cause.

Body weight, as determined by body mass index (BMI), was also strongly correlated with delay discounting, suggesting that people who don’t place a high value on future rewards tend to have a higher BMI.

Another linked smoking initiation and delay discounting, suggesting people who undervalue future rewards may be more likely to start smoking and less likely to quit if they did.

“This is a fascinating and very important finding,” said MacKillop. “Delay discounting has been shown to predict smoking cessation failure previously, but these findings suggest that link is by way of common genetic contributors for the first time.”

The team also determined that delay discounting negatively correlated with three cognitive measures, including college attainment, years of education and childhood IQ.

The researchers are hoping to expand the study to a larger and more diverse population.

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