University, Genetics Firm Find Link Between ADHD, Delay Discounting

Allison Inserro

Would you rather have $60 today or $75 next month? Using similar questions, university researchers and a direct-to-consumer genetics company found a genetic signature for delay discounting that overlaps with attention-deficit/hyperactivity disorder (ADHD), smoking, and weight.

Delay discounting is the tendency to undervalue future rewards. In this study that included data from more than 23,000 genotyped research participants, neuroscientists at the University of California San Diego (UCSD) School of Medicine teamed up with 23andMe Inc. By partnering with a private company, an author of the study said they had created “a new model for science” by removing cost prohibitions and shaved off years of research.

Results showed that approximately 12% 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 December 11 in Nature Neuroscience.

"Studying the genetic basis of delay discounting is something I've wanted to do for the entirety of my 20 years of research, but it takes a huge number of people for a genetics study to be meaningful," senior author Abraham Palmer, PhD, professor of psychiatry and vice chair for basic research at UCSD School of Medicine, said in a statement. "By collaborating with a company that already has the genotypes for millions of people, all we needed was for them to answer a few questions.”

"In less than four months, we had responses from more than 23,000 research participants," said Pierre Fontanillas, PhD, a senior statistical geneticist at 23andMe. "This shows the power of our research model to quickly gather large amounts of phenotypic and genotypic data for scientific discovery." The 23andMe customers consented to participate in the research.
Palmer said every complicated nervous system needs a way of assessing the value of current versus delayed rewards. "A person's ability to delay gratification is not just a curiosity, it's integrally important to physical and mental health," Palmer said. "In addition, a person's economic success is tied to delay discounting. Take seeking higher education and saving for retirement as examples -- these future rewards are valuable in today's economy, but we're finding that not everyone has the same inclination to achieve them."

The team found a number of genetic correlations by comparing participants' survey responses to their corresponding genotypes and complementary data from other studies.

"We discovered, for the first time, a genetic correlation between ADHD and delay discounting," said first author Sandra Sanchez-Roige, PhD, a postdoctoral researcher in Palmer's lab. "People with ADHD place less value in delayed rewards. That doesn't mean that everyone with ADHD will undervalue future rewards or vice versa, just that the two factors have a common underlying genetic cause."

The researchers also found that delay discounting is genetically correlated with smoking initiation. In other words, people who undervalue future rewards may be more likely to start smoking and less likely to quit if they start.

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.

In addition, the team found that delay discounting negatively correlated with 3 cognitive measures: college attainment, years of education and childhood IQ.

Sanchez-Roige S, Fontanillas P, Elson SL, et al; 23andMe Research Team. Genome-wide association study of delay discounting in 23,217 adult research participants of European ancestry [published online December 11, 2017]. Nat Neurosci. doi: 10.1038/s41593-017-0032-x.
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