RealClearScience Journal Club

Science Figures Interpreted and Analyzed by RealClearScience

Drug Overdose: The Real American Epidemic

Alex B. Berezow - November 24, 2014

Recently, there has been much talk of various "epidemics" in America. The three most commonly mentioned are suicide, gun violence, and drug overdose. A close examination of the data, however, reveals two surprises: First, one of them is not actually an epidemic. Second, one of them is a much bigger epidemic than most people realize. (See chart.)

The "suicide epidemic" (red line) has received the most attention as of late. This is for good reason. At a rate of 12.54 deaths per 100,000 Americans, the suicide rate is at a 25-year high. The CDC, which provides publicly accessible data (via WISQARS) from 1999 to 2012, shows that the suicide rate over that period has increased by nearly 19.7%.

Similarly, school shootings and other mass killings result in highly partisan debates about the "gun violence epidemic." However, the CDC data does not show that this even is an epidemic. Instead, the homicide-by-firearm rate (purple line) has been declining from a high of 4.27 per 100,000 in 2006 to 3.76 per 100,000 in 2012, a roughly 12% drop. The average American is more than three times as likely to commit suicide than to be shot and killed.

The most shocking data are the deaths due to unintentional drug poisonings (green line). From 1999 to 2012, deaths by drug overdose increased from 4.00 per 100,000 to 10.54 per 100,000, a whopping 164% increase. While the suicide rate has slowly climbed over the past decade, the death rate from unintentional drug overdoses has skyrocketed. Indeed, the term "epidemic" was invented for trend lines like this. (Note: More detailed information on what exactly constitutes unintentional drug poisoning can be found in the ICD-10 under codes X40-X49.)

It should be noted that accidental drug overdoses include far more people than just celebrities and gangbangers who snort cocaine and guzzle alcohol. Indeed, a substantial proportion of overdoses are with prescription drugs, such as opioids (e.g., OxyContin, Vicodin) and benzodiazepines (e.g., Xanax, Valium, Ativan). Additionally, as reported this week in an article appropriately titled "The Great American Relapse," The Economist notes that heroin is making a comeback. Deaths from heroin overdoses have doubled from 2010 to 2012 as opioid painkiller addicts forego expensive prescription meds for cheaper heroin from the street.

As it turns out, our society's habit of reaching for the medicine cabinet for every (heart)ache and pain is quite literally killing us.

The explosive growth in the number of deaths due to unintentional drug overdoses is nothing short of a national emergency. Yet, the phenomenon gets very little attention in the popular press. Unfortunately for our highly medicated society, this is one problem that we cannot solve by popping more pills.

Source: Centers for Disease Control and Prevention, National Center for Injury Prevention and Control. Accessed: 23-Nov-2014.

(AP photo)

Have Men Reached the Limits of Running?

Ross Pomeroy - November 21, 2014

For decades, mankind's physical abilities have steadily increased. With every broken world record, humans have demonstrated the potential to throw farther, run faster, and jump higher. More recently, scientists, athletes, and spectators alike have wondered if or when we'll reach a ceiling. A new study published in PLoS ONE shows that, as far as distance running is concerned, we may be getting close.

Researchers from the University of Washington and the Mayo Clinic teamed up to analyze the 40 fastest male performances in the 5,000 meters, the 10,000 meters, and the marathon for each year from 1980 to 2003. They also tallied and plotted the number of athletes who turned in elite performances each year, deemed to be under 13:20 for the 5000 meters, 27:45 for the 10000 meters, and 2:10 for the marathon (shown below).

The researchers found that, for the past decade, performance in the 5,000 and 10,000-meter races has leveled off. In fact, there have been no new world records for either since 2004 and 2005 respectively, the longest gap between world records since the 1940s.

Men still seem to be making progress in the marathon, however. In fact, the world record (still pending official ratification) was set at the Berlin Marathon in September. Kenya's Dennis Kimetto ran the 26.2 miles in 2:02:57.

"All indices of [marathon] speed show a nearly linear increase in speed with an increased number of elite performances over the three plus decades we sampled," lead researcher Timothy Kruse reported.

Kruse and his colleagues announced three possible interpretations of the data. First, improved drug testing may be preventing athletes from using compounds like erythropoietin to boost the number of red blood cells in the blood stream and thus improve their aerobic capacity, a process colloquially known as "blood-doping." Second, more lucrative financial incentives for marathons may have drawn elite runners away from the 5,000 and 10,000-meter events. And third, men may be nearing a "physiological upper limit."

As men near the 2-hour mark for the marathon, which would require a blistering average speed of 13.1 miles per hour, many openly wonder whether or not that milestone will be eclipsed. If current trends continue, it's certainly possible.

Source: Kruse TN, Carter RE, Rosedahl JK, Joyner MJ (2014) Speed Trends in Male Distance Running. PLoS ONE 9(11): e112978. doi:10.1371/journal.pone.0112978

Active Moms May Be the Cure for Obesity

Ross Pomeroy - November 18, 2014

As Americans collectively remain overweight and obese, many scientists have sought to understand precisely why this is so. Most broadly, the answer is tied to socioenvironmental evolution, which encompasses a host of factors. For example, we're eating differently than we used to, we're eating more than we used to, and we're moving a lot less than we used to.

Now that we've gotten ourselves stuck in such a heavy state, scientists are concerned that it will be difficult to dislodge ourselves. Specifically, if studies in mice are any indication, obesity risk may be transferable to offspring via epigenetics. In other words, parental obesity may effect how children's genes are expressed, making kids more likely to store excess calories as fat and more likely to develop diabetes. Considering that the rate of childhood obesity has more than doubled in the past thirty years, this is certainly possibly. However, more research needs to be performed, to first convincingly confirm these effects in humans, and then to potentially create treatments to counter them.

Today, in the journal Mayo Clinic Proceedings, post-doctoral researcher Dr. Edward Archer of the University of Alabama provided a theoretical framework to help guide these efforts. He dubbed his idea the Maternal Resources Hypothesis. Formed via an analysis of the current scientific literature, it states that because mothers are, on average, eating more and exercising less than in years past, they are storing more energy as fat and passing on more nutrients to fetuses in utero, resulting in larger babies with more fat at birth. Larger babies, coupled with a more sedentary lifestyle during childhood, means that these children will be predisposed to obesity. Since the number of fat cells is largely set during childhood, obesity early on can elevate a person's risk for obesity for the rest of their life. If, indeed, these children remain obese into adulthood and have children, the cycle continues.

Archer's hypothesis is intriguing. Now that it's out there, future studies will either confirm or refute it.

If it does prove correct, Archer believes that it highlights a key tool to alleviating the current obesity pandemic. He urges women planning on motherhood to be physically active throughout their entire lives in order to prepare their metabolisms for pregnancy and thus have metabolically healthy children.

"Active moms are the cure," Archer said.

The onus for obesity isn't only on moms, however. Last year, a study showed that children born to obese fathers had discernible differences in gene expression compared to children born to normal weight fathers.

Would-be moms and dads should strongly consider living a lifestyle that involves eating less and moving more. Not just for themselves, but for their kids.

Source: Archer, Edward. "The Childhood Obesity Epidemic as a Result of Nongenetic Evolution: The Maternal Resources Hypothesis." Mayo Clin Proc. n Dec 2014;

Simmer Down: Viruses Not 'Fourth Domain' of Life

Alex B. Berezow - November 17, 2014

Biologists have categorized life into three large domains: Bacteria, Archaea (weird, bacteria-like microbes), and Eukarya (unicellular and multicellular organisms such as fungi, plants, and animals that possess nucleated cells). Under this classification system, viruses are left out in the cold. They certainly are not "alive" in the classical sense because they are not capable of metabolizing or replicating on their own. But it does not feel quite right to classify them as "inanimate," either, because they are built of biological molecules and contain genetic information. Thus, for the most part, viruses languish in the no man's land between the living and the dead.

The debate about how to classify viruses received a jolt with the discovery of extremely large viruses (such as Pandoravirus) that are so gigantic they can be seen with a light microscope and contain more genetic information than some bacteria. It has been proposed, due to some intriguing similarities in DNA sequences -- specifically, in the gene that encodes for an enzyme called RNA polymerase -- that such large viruses actually constitute a "fourth domain" of life. If that is the case, then perhaps all viruses should be awarded this new status.

"Sacrebleu!" say French scientists in a recent issue of Trends in Microbiology. Considering viruses to be a fourth domain would unnecessarily complicate evolutionary biology. For instance, the authors indicate that using RNA polymerase to redraw the tree of life presents a gigantic challenge. Large viruses do not all cluster into a single new domain. Instead, classifying life based on RNA polymerase would likely demand the creation of several new domains. (See figure.)

Such a phylogenetic tree is unwieldy, or as evolutionary biologists call it, "non-parsimonious." A foundation of building evolutionary trees is that they ought to be as simple as possible. This is referred to by scientists as the principle of parsimony but is more colloquially known as Occam's Razor. Essentially, a model that requires fewer assumptions (in this case, evolutionary changes) is superior to a model that requires more.

This is not the only problem with a viral fourth domain. The biggest difference between cells and viruses is their method of replication. All three domains of life replicate by cell division, which implies that this trait was derived from the Last Universal Common Ancestor (LUCA). (In other words, LUCA is the theoretical ancestor of Bacteria, Arcahea, and Eukarya.)

Viruses, which do not replicate by cell division, probably evolved independently multiple times, "here, there, and everywhere," as the authors conclude. Some probably evolved before LUCA, and others well after LUCA. Many have likely exchanged genetic material via horizontal gene transfer. Lumping them all into a fourth domain, therefore, makes little sense.

Though the debate over the classification of viruses may at first seem to be purely academic, it touches upon underlying questions that are of much greater significance: What exactly is life, and how did it evolve? The answer to those questions may be partially found within the enigmatic world of the viruses.

Source: Patrick Forterre, Mart Krupovic, and David Prangishvili. "Cellular domains and viral lineages." Trends in Microbiology, 22 (10): 554-558. October 2014. 

Ancient Reptile Is Either Adorable or Terrifying

Ross Pomeroy - November 13, 2014

Around 252 million years ago, a Great Dying occurred. In a geologic blink of an eye, 96% of all marine species and 70% of all terrestrial species went extinct. Volcanoes, rapid climate change, or an asteroid impact may have been to blame; it could have even been all of the above. Regardless of what caused the Great Dying, the effect was akin to hitting a giant "reset" button on Earth. The planet became a blank slate, and new species emerged to write their stories.

It was in this setting that paleontologists believe that Garjainia madiba, a newly discovered species of reptile, thrived. G. madiba belonged to the Erythrosuchidae family, a group of apex predators that gained a widespread foothold on the new Earth. Closely related to modern day Crocodilians, the erythrosuchids are known for their distinct, large, and deep head, making them kind of "cute." The largest among them was Erythrosuchus, which sported a massive head on a squat frame. Erythrosuchus was 16 feet long and 7 feet tall.

G. madiba was big, but it wasn't that big. Estimates put its length at around 6 feet. The smaller size likely suited it just fine, however. In the wake of the Great Dying, much of the bigger land animals had died off, so G. madiba may have been one of the largest at the time. Geologically, it's been pinned down as the oldest known erythrosuchid in the southern hemisphere. Larger species like Erythrosuchus likely evolved later on.

The current G. madiba fossil was found in South Africa, but another was found in Europe. To the group of paleontologists who described the discovery yesterday in PLoS ONE, that demonstrates "that erythrosuchids became established as the largest terrestrial predators across a broad swath of Pangaea within five million years of the end-Permian mass extinction event."

(Images: Mark Witton, Dmitry Bogdanov)

Source: Gower DJ, Hancox PJ, Botha-Brink J, Sennikov AG, Butler RJ (2014) A New Species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa. PLoS ONE 9(11): e111154. doi:10.1371/journal.pone.0111154

Sci-Fi Now Reality: Mind Control of Gene Expression

Alex B. Berezow - November 11, 2014

Mind control -- specifically, the ability to manipulate machines or the environment through the power of our thoughts -- has long been the fascination of sci-fi enthusiasts. Now, a team of European researchers has made a giant leap toward turning this sci-fi fantasy into reality: They have demonstrated human mind control of gene expression in a mouse. And, they used some of the best tools of neuroscience, physics and synthetic biology to accomplish it.

Volunteers were trained how to generate different mental states, such as concentration or meditation, which produce fluctuations in neuronal voltage that are more commonly known as brain waves. Subjects wore an EEG (electroencephalography) headset that detected the brain waves and interpreted the mental state. The data was then sent, via Bluetooth (the same technology that connects a smartphone to a wireless headset or to a car stereo), to a small computer. Based on the mental state, the computer sent either an ON or OFF signal to an electromagnetic field generator. (See diagram below.)

When the subject was meditating, the field generator was sent an ON signal, and it created an alternating magnetic field. This allowed the authors to utilize wireless energy transfer which, as its name implies, powers a device without the use of wires. The alternating magnetic field created by the transmitter coil induced an electric current in a receiver coil, which ultimately powers the device. (This phenomenon, known as induction, is also used to power electric toothbrushes and alerts stoplights to the presence of a car.) In this case, the device is a special implant placed on the back of a mouse under its skin. When the implant was powered, it turned on a near-infrared light.

The light, in turn, activated a pathway genetically engineered into cells that were also placed inside the implant in a cultivation chamber. (See diagram below.)

The photons activated a protein (DGCL) taken from the photosynthetic bacterium Rhodobacter. When exposed to near-infrared light, the protein creates a metabolite called c-di-GMP, which is sensed by a protein receptor called STING. Ultimately, STING results in the activation of yet another genetically engineered gene that encodes an enzyme called SEAP. This enzyme was secreted into the blood of the mouse, and its presence could be detected with a simple chemiluminescence assay.

In summary: Brain waves --> Bluetooth (microwave photons) --> Electric current --> Magnetic field --> Another electric current (in the implant) --> Near-infrared photons --> Activation of cellular genetic pathway --> Enzyme produced and secreted into the blood.


Immediate applications for this technology are probably still years (decades) away. But, the idea of altering gene expression by the power of thought alone is both intriguing and frightening.

Source: Marc Folcher et al. "Mind-controlled transgene expression by a wireless-powered optogenetic designer cell implant." Nature Communications 5:5392. Published online: 11-Nov-2014. DOI: 10.1038/ncomms6392

(AP photo)

A Universe of Stars May Exist Outside Galaxies

Ross Pomeroy - November 6, 2014

In 1998, researchers using the Hubble Space Telescope made an astounding discovery. Gazing at the Virgo Cluster of galaxies a dizzying 53.8 million light years distant, they spotted 600 red giant stars adrift in intergalactic space. Ripped from their home galaxies during tumultuous collisions with others, the stars were no longer governed predominantly by the gravity of one galaxy, but by the faint, distant pulls of many. Artists imagined the skies of planets in orbit around these lonely stars: blank and dark, flecked only with the "fuzzy apparitions" of nearby galaxies.

At the time, the study's lead astronomer Harry Ferguson estimated that there might be as many as 10 million more of these "rogue" stars in the Virgo Cluster, stars less luminous than red giants and thus too indistinct to see with any certainty. A new report published in the journal Science shows that Ferguson may have vastly underestimated their number.

According to the study, as many as half of the universe's stars may dwell outside of galaxies, representing a stellar population previously unknown to science!

Caltech astrophysicist Michael Zemcov led the international team of researchers that contributed to the fascinating finding, which materialized out of an effort to explain fluctuations in the Extragalactic Infrared Background light (EBL), basically all of the accumulated radiation in the universe resulting from star formation. Analyzing data collected from the CIBER mission, an orbiting instrument with tools specifically designed to observe the EBL, the researchers determined that light from stars stripped from their galaxies best explained the fluctuations, ruling out effects from primordial galaxies and black holes in the process.

"If confirmed, these observations reveal an unexpected stellar population, with as many as half the stars in the local universe being outside galaxies," NASA astronomer Harvey Moseley commented. "It is remarkable that such a major component of the universe could have been hiding in plain sight as an infrared background between the stars and galaxies."

The presence of all these intergalactic stars would also help explain another peculiar mystery, Zemcov notes. Currently, the light produced from known populations of galaxies and quasars is not nearly enough to explain observations of hydrogen, which serves as an accurate proxy for the amount of light in the universe. In other words, there are far more photons of light than there should be. The quandary has been termed the "photon underproduction crisis."

The Carnegie Institute of Washington’s Juna Kollmeier described the baffling puzzle thusly: "It's as if you're in a big, brightly-lit room, but you look around and see only a few 40-watt lightbulbs."

The stars residing outside of galaxies could very well be those missing lightbulbs, or at least some of them anyway.

Stars go rogue when they are ejected from their home galaxies as a result of galaxy collisions. In the cosmic sense, interactions between the one hundred billion galaxies in the known universe are actually quite common, and have likely occurred many, many times over the 13.8 billion year lifespan of the universe. Our own Milky Way Galaxy is set to collide with the Andromeda Galaxy in roughly four billion years. Seeing as how our sun will still be around by that time, it potentially could join the newly found and immense population of intergalactic stars, and the Earth may find itself along for the ride.

Source: Zemcov et. al. "On the origin of near-infrared extragalactic background light anisotropy." Science 7 NOVEMBER 2014 • VOL 346 ISSUE 6210

(Image: H. Ferguson (STScI), N. Tanvir (IoA), T. von Hippel (U. Wisc.), NASA)

These Are the Most Common Sexual Fantasies

Ross Pomeroy - November 3, 2014

Sexual fantasizing is a notoriously closeted subject. This silence is problematic, however, as it reinforces the notion that fantasizing is abnormal, and that those who do so are deviants. However, a new study shows that -- far from being abnormal -- sexual fantasizing is quite common.

Until now, no large-scale study in the general population has been conducted to identify the prevalence of specific fantasies. Researchers Christian Joyal, Amélie Cossette, and Vanessa Lapierre sought to fill that information void.

"Our main objective was to specify norms in sexual fantasies, an essential step in defining pathologies," Joyal said. "And as we suspected, there are a lot more common fantasies than atypical fantasies.

Joyal, Cossette, and Vanessa asked 1,516 participants from a large city in Quebec. Subjects were 52.7% female and 47.3% male, with an average age of around thirty. Participants anonymously completed an in-depth, online questionnaire to gauge the prevalence of certain sexual fantasies, as well as their intensity of interest in each.

Here are the twenty most common sexual fantasies for men and women:


  1. Having sex in a romantic location like on a deserted beach. (84.9%)
  2. Having sex in an unusual place, such as in the office or a public toilet. (81.7%)
  3. Taking part in fellatio or cunnilingus. (78.5%)
  4. Giving fellatio. (72.1%)
  5. Being masturbated by my partner. (71.4%)
  6. Masturbating my partner. (68.1%)
  7. Having sex with someone that I know who is not my spouse. (66.3%)
  8. Being dominated sexually. (64.6%)
  9. Making love openly in a public place. (57.3%)
  10. Having sex with more than three people, both men and women. (56.5%)
  11. Being tied up by someone in order to obtain sexual pleasure. (52.1%)
  12. Having sex with a star or a well-known person. (51.7%)
  13. Having sex with an unknown person. (48.9%)
  14. Dominating someone sexually (46.7%)
  15. Watching two women make love. (42.4%)
  16. Tying someone up in order to obtain sexual pleasure. (41.7%)
  17. That my partner ejaculates on me. (41.3%)
  18. Having homosexual sex. (36.9%)
  19. Having sex with two women. (36.9%)
  20. Being masturbated by an acquaintance. (36.8%)


  1. Taking part in fellatio or cunnilingus. (87.6%)
  2. Having sex with two women. (84.5%)
  3. Having sex with someone that I know who is not my spouse. (83.4%)
  4. Having sex in an unusual place, such as in the office or a public toilet. (82.3%)
  5. Watching two women make love. (82.1%)
  6. Ejaculating on my sexual partner. (80.4%)
  7. Having sex in a romantic location like on a deserted beach. (78.4%)
  8. Giving cunnilingus. (78.1%)
  9. Masturbating my partner. (76.4%)
  10. Having sex with more than three people, all women. (75.3%)
  11. Having sex with an unknown person. (72.5%)
  12. Being masturbated by my partner. (71.7%)
  13. Having sex with a women with very large breasts (68.6%)
  14. Making love openly in a public space. (66.1%)
  15. Masturbating an acquaintance. (65.9%)
  16. Being masturbated by an acquaintance. (64.7%)
  17. Having anal sex. (64.2%)
  18. Watching someone undress without him or her knowing (63.4%)
  19. Being masturbated by an unknown person. (62.5%)
  20. Masturbating an unknown person. (62.4%)

"This study indicates that there are very few statistically unusual sexual fantasies," the researchers noted. But some were noticeably rare. Fewer than 10% of respondents fantasized about wearing clothing from the opposite sex or urinating on a partner or being urinated on. Fewer than 3% of respondents reported fantasizing about having sex with an animal or a child.

The researchers encourage a measure of caution when interpreting the numbers. Previous research has shown that volunteers in sexually-focused studies tend to be more open than people who refuse to participate in such studies, so that may have biased the results. Moreover, since the survey was entirely conducted online, the researchers were not able to visually confirm the subjects' age and gender.

Source: Joyal, C. C., Cossette, A. and Lapierre, V. (2014), What Exactly Is an Unusual Sexual Fantasy?. Journal of Sexual Medicine. doi: 10.1111/jsm.12734

H7N9: The Next Influenza Pandemic?

Alex B. Berezow - November 3, 2014

Since May of this year, 440 Chinese people have been infected with a new strain of influenza subtype H7N9, and 122 of them have died. Though the case-fatality rate suggested by this data is greatly inflated by asymptomatic and mild (and hence, unreported) cases, a new analysis in Trends in Microbiology suggests that the virus has the potential to become the next influenza pandemic.

Where did this new H7N9 strain come from? Genetic analyses suggest that four different avian influenza viruses swapped genes in a process known as "reassortment." (See figure.)

The influenza genome consists of eleven genes on eight RNA segments, meaning that each RNA segment encodes only one or two genes. (Pause just a moment to think about that: A microscopic particle consisting of a mere eleven genes is able to kill 250,000 to 500,000 human beings every single year. Incidentally, Ebola virus only has seven genes.)

Due to its genomic structure and the fact that a single animal can be infected by more than one strain at a time, influenza is prone to reassorting its genome. In other words, RNA segment #1 from influenza virus X can be replaced by the same RNA segment from influenza virus Y. In the case of H7N9, it is believed that the "H7" gene came from avian influenza subtype H7N3, recently found in Chinese ducks, and that the "N9" gene came from either avian influenza subtype H2N9 or H11N9, both of which have been found in migratory birds. The six remaining RNA segments appear to have come from two different strains of H9N2.

Such genetic shuffling is quite common and is often responsible for influenza pandemics. The reason is that new genetic combinations fool our immune systems; antibodies we might have against say, H1N1, are completely useless against H7N9 and other subtypes.

Currently, the H7N9 strain is infecting mostly elderly men with underlying health issues who likely came into direct contact with live poultry. But, this could change. Once the virus is in humans, natural selection may favor the production of viruses that transmit more easily between humans. Such a transition probably would require very slight mutations in the "H7" gene (more properly called HA), as well as the gene PB2, which encodes an enzyme that helps replicate the viral genome.

Disturbingly, the authors believe that H7N9 possesses a greater pandemic potential than H5N1, which already has been spreading around the globe. Indeed, the authors conclude:

"...these viruses exhibit high replicative ability and limited transmissibility in mammals, have acquired mammalian-adapting amino acid changes, may reassort with circulating human viruses (based on the reported coinfection of a patient with H7N9 and human H3N2 viruses), and readily acquire resistance to the NA inhibitor oseltamivir."

As always, there is no reason to panic, but you can be certain that epidemiologists are keeping a close eye on H7N9.

Source: Tokiko Watanabe, Shinji Watanabe, Eileen A. Maher, Gabriele Neumann, Yoshihiro Kawaoka. "Pandemic potential of avian influenza A (H7N9) viruses." Trends Microbiol pii: S0966-842X(14)00179-6. Published online: 2014-Sep-25. doi: 10.1016/j.tim.2014.08.008.

(AP photo)

These Two Genes Are Linked to Murder

Ross Pomeroy - October 28, 2014

Scientists in Finland have identified two genes associated with severe violent behavior. They report their results in the journal Molecular Psychiatry.

The first candidate is monoamine oxidase A, or MAOA for short. MAOA is a key regulator of dopamine levels in the brain.

A multifaceted hormone, dopamine plays diverse roles within the human body. In the brain, it controls feelings of arousal, award, and motor control, among others.

The researchers specifically focused on a low-activity version of the MAOA gene. Previously termed the "warrior gene," it doesn't regulate dopamine as effectively. Prior studies have demonstrated that subjects with the "warrior gene" display higher levels of aggressive and antisocial behavior.

The second gene candidate is a variant of T-cadherin, or CDH13, which specifically codes for a protein that affects the cell linings of neurons. CDH13 is already thought to be the most important genetic contributor to attention-deficit hyperactivity disorder. The association suggests a link to impulsive behavior.

The Finnish scientists gleaned the results from a group of 753 inmates incarcerated in Finland's 19 largest prisons. The group comprised 215 non-violent offenders, in jail for offenses like drunk-driving or drug distribution, and 538 violent offenders, who committed at least one act of murder, attempted murder, manslaughter, attempted manslaughter, or battery. Violent offenders who committed more than ten crimes were further classified into an "extremely violent" subgroup. 84 of them fit the bill.

Genetic testing showed that members of this extremely violent subgroup were much more likely than non-violent criminals to have the low-activity MAOA gene and the CDH13 variant.

Despite the strong results, the researchers make clear that the genetics of criminal behavior is a young science. It's far too early to even consider screening individuals for potential violent inclinations, nor should somebody's genotype be considered in the courtroom.

Though people with the low-activity MAOA gene and the CDH13 variant may be more likely to commit a violent crime, violent crime itself is a rare act, so the chance that they will commit one is still remote. The researchers conservatively estimate that 5–10% of all severe violent crime in Finland is attributable to the two genes.

Source: J Tiihonen et. al. "Genetic background of extreme violent behavior." Molecular Psychiatry (2014), 1–7

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