Delay discounting (DD) is the tendency to decline a larger reward someone will receive later for a smaller award they can have immediately — and it may be influenced by our genetic makeup, according to new research presented during this week's American College of Neuropsychopharmacology annual meeting in Hollywood, Fla.

"[DD], preference for smaller immediate rewards over larger but delayed rewards, is an established behavioral model of impulsive choice, a key component of a broader impulsivity construct," Dr. Andrey Anokhin and his colleagues from the Washington University School of Medicine explained. "Elevated DD has been implicated as a potential intermediate phenotype (endophenotype) for a range of psychopathologies characterized by impulsive decision making, most notably, addictions and psychopathology. … However, few studies examined genetic influences on DD in humans."

Researchers had 601 twins aged 16 to 20 complete a computerized DD test in order to measure age-related changes in DD, "long-term stability of individual differences, heritability, and the potential role of genetic variant in the 5-HT system in the determination of DD." This 5-HT is considered vital to learning and memory, as are all its receptors.

The test revolved around money, asking twins at age 12 and age 14 if they were given the choice to receive $7 immediately or $10 in the mail two weeks later, which would they choose? At age 12, 35 percent decided to take $7 right away versus more money later. But this number fell to 35 percent when twins were 14.

Overall, researchers found a modest but significant decrease with age, which suggests impulsive choices and behavior gradually improve as we get older. Because participants were twins, "the researchers were able to use mathematical formulas to analyze the impact of genetic factors on their decisions," according to a press release.

The genetic analysis revealed serotonin genes were involved. Upon a closer look, however, researchers found genes related to kappa opioid receptors on brain cells were more crucial in impulsive decision-making — the three together were considered the top genes linked to those receptors.

Anokhin said "these impulsivity genes may include genes coding for enzymes that synthesize the neurotransmitter serotonin and receptors where serotonin binds in the brain." It's still too early to say for sure if the ability and tendency to choose and act impulsively is something to blame on our parents.

If impulsivity is inherited, it will be important for researchers to determine the exact "delay discounting genes" and their coding proteins. These genes could also have the potential to help us understand the basis of psychiatric disorders marked by impulsive behavior, such as alcoholism, drug addiction, and obesity.

"We need to look more closely before drawing conclusions, but we want to see what the consequences of the differences we’ve identified are for real-life behaviors," he said.

Source: Anokhin A et al. Genetics of delay discounting in humans: Heritability and preliminary evidence for genetic association. American College of Neuropsychopharmacology annual meeting. 2015.