Researchers from the University of Bonn and the Central Institute of Mental Health in Mannheim found that “pro­blematic” Internet users, especially women, are more often carriers of a variation in the CHRNA4 gene, the nicotinic acetylcholine receptor gene, which that also plays a major role in nicotine addiction and generation of dopamine.

The T- variant (CC genotype) of the rs1044396 polymorphism on the CHRNA4 gene occurred significantly more frequently*, the researchers report. “The CC variant of rs1044396 has been associated with significantly higher trait anxiety and smoking,” the researchers note.

Over the past years, the Bonn researchers interviewed a total of 843 people about their Internet habits. An analysis of the questionnaires showed that 132 men and women in this group exhibited “problematic behavior” in how they handle the online medium, and they selected that group for the study. (There was no significant difference in smoking status.)

The research used a measure of generalized Internet addiction called the Internet Addiction Test, which has 20 items that measure “different facets of Internet addiction such as the Web’s impact on social or work life.”

The researchers state that for the selected group, “all their thoughts revolve around the Internet during the day, and they feel their well being is severely impacted if they have to go without it.” The study found the “addicts” spent 16.85 a week (2.4 hours a day) on the Internet in leisure, vs. 9.68 per week for controls.

What exactly is “Internet addiction”?

The researchers admit that the poorly defined research term “Internet addiction” is “still a matter of debate, because people are not addicted to the Internet per se, but to diverse contents of the World Wide Web such as the use of multiplayer-online games, social networks, or pornography. The researchers note that “Internet addiction” is included in the appendix of the DSM-5, “showing its potential to be acknowledged as an own behavioral addiction in the future.”

“A limitation of this study is that our investigated group of Internet addicts only consists of persons with occasional but not frequent problems in everyday life due to the use of the Internet” and ”it needs to be tested whether CHRNA4 also targets specialized Internet addiction, such as excessive use of social media. … A last limitation of this study represents the rather small sample size.”

Internet addiction has a prevalence between 0.3% and 10.6% in the population, depending on the investigated country culture, according to a 2008 study.

However, Internet addiction is estimated to be only about 1% in Germany, suggesting limitations on selecting a relevant and useful study population.

UPDATE 8/31/2012:

* 36 subjects (out of a total of 132 participants with problematic Internet use, after screening 850 participants) had the T- variant (CC genotype) of the rs1044396 polymorphism on the CHRNA4 gene vs. 22 out of a total of 132 for controls. For males it was 18 vs. 15 for controls and for females it was 18 vs. 7 for controls.)

“Given our a priori hypothesis together with the significant statistics (which hold for multiple testing), I am convinced that the results are robust,” lead author Dr. Christian Montag told KurzweilAI. “Nevertheless there is a BUT: in molecular genetics replication studies are of special importance and we’d like to encourage other work groups to look at this issue.”