In every group of guys, there's usually one crazy dude. Call him Craig—"CrayCraig," to your girlfriend. Craig's the bro who calls you up on a Tuesday because he needs a partner for skydiving. He's the bro who randomly drops his whole paycheck on a new convertible and then gets pulled over a day later for speeding in it. And while Craig doesn't drink any more than the average guy, things get ugly when he gets a little booze in his system. He's the "angry drunk" who's always trying to buy tequila shots for everyone, then pick fights with guys twice his size, then drive home in a shopping cart. That's Craig.
Now, scientists might have an explanation for why Craig does all that: It's in his genes.
People with a mutated form of the HTR2B gene have a tendency to become more impulsive, violent, and reckless when they drink, according a study published in the Nature journal Translational Psychiatry. Researchers in Finland noticed that a small group of 14 Finnish people who carried the mutated gene—and who had consumed alcohol—were far more likely to pick fights, explode into aggressive outbursts, impulsively spend huge amounts of cash, and have risky sex when compared to 156 normal people. Carriers of the mutant gene weren't necessarily alcoholics, but they were far more impulsive generally, and especially after drinking.
The mutation "caused impulsive behaviour while under intoxication, and that included impulsive sex, impulsively spending money, and driving under the influence,” study author Roope Tikkanen told The Guardian. “When they are sober they have a tendency towards impulsivity, but our discovery is that it will be enhanced by small amounts of alcohol,” he said. None of the study participants were violent offenders.
Again, a key detail: "Small amounts of alcohol." Zoom out a little bit, and the study points to a broader trend about how alcohol can affect people differently, especially if they have a prexisting neuropsychological condition triggered by alcohol's psychoactive effects. People with these problems aren't (necessarily) bad people, nor should their neurochemical problems get projected as some kind of moral flaw. In other words: Craig's not necessarily mean or pugnacious or "angry"—alcohol just hits him a lot harder than it does other people.
The HTR2B gene ordinarily helps control the brain's serotonin production, but the mutation seems to cause a chemical imbalance. “The interesting thing about this is that it tells us something about the mechanism of the serotonin receptor globally. It’s like a laboratory experiment that you can’t usually do in humans,” Tikkanen said.
The researchers focused on the genetically distinct population of Finland, and found that 2.2% of the population (more than 100,000 people) have the genetic mutation.
But regardless of whether Craig is Finnish or not, blaming his impulsive behavior on genes is a no-win solution. Affected people should "attend courses to help them keep their alcohol consumption within healthy limits, and have therapy to boost their self control," Tikkanen said.