From: drarwingnuttephd@gmail.com   
      
   Murderers May Be Hardwired to Kill   
   OCT 28, 2014 07:45 AM ET // BY JENNIFER VIEGAS   
       
      
      
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   Serial killers and other people who repeatedly commit violent crimes, such as   
   assault and battery, may be hardwired to hurt others, suggests a new study   
   that identifies two genetic variants tied to extreme violent behavior.   
      
   The findings, published in the latest issue of the journal Molecular   
   Psychiatry, could help to explain why the majority of violent crimes are   
   committed by a small group of antisocial, repeat offenders. The extensive   
   study represents the first effort to    
   investigate the genetic background of people exhibiting such repetitive,   
   brutal behavior.   
      
   "I think that we have found two genes that have the largest effect in   
   aggressive behavior, and that there are probably tens or hundreds of other   
   genes having smaller effects," lead author Jari Tiihonen told Discovery News.   
      
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   Tiihonen, a professor in the Department of Clinical Neuroscience at the   
   Karolinska Institute in Sweden, and his colleagues screened 1004 prisoners in   
   Finland. Of that group, 184 refused to participate in the study and 26 were   
   excluded because of "a    
   psychosis diagnosis." Blood samples for DNA extraction were taken from the   
   remaining prisoners, whose crimes and backgrounds were also investigated.   
      
   The scientists determined that the prisoners who had repeatedly committed, or   
   attempted to commit, violent crimes tended to have one or both of the   
   following genetic variants: CDH13 and MAOA, a.k.a. the "warrior gene."   
      
   Tiihonen explained that MAOA metabolizes an important neurotransmitter called   
   dopamine. The presence of this genetic variant and substance abuse helps to   
   create a perfect storm.   
      
   "If this activity is decreased, it might lead to a larger dopamine burst in   
   the brain when alcohol, cocaine or amphetamine is used," he explained. "It is   
   known that these substances induce dopamine burst and aggression."   
      
   CDH13, on the other hand, is a gene that codes for neuronal adhesion protein,   
   so it contributes to the development of neuronal connections in the brain. It   
   is one of the most important genes associated with Attention Deficit   
   Hyperactivity Disorder (ADHD).   
      
   People with both of these genetic variants have a 13-fold increase of   
   committing a violent crime versus those who do not have the mutations,   
   according to the study. Add substance abuse again to the mix and there is a   
   likely recipe for disaster.   
      
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   The study could also help to explain why most mass murderers are men.   
      
   "Since MAOA is located in the X-chromosome, men have only one copy of the gene   
   and women have two copies," Tiihonen said, explaining that women have two   
   X-chromosomes. "Therefore, females can have one low activity allele   
   (alternative form of a gene that    
   arises by mutation) and one high activity allele, but if males have a low   
   activity allele, they cannot have another allele functioning more efficiently   
   because they have only one copy of the gene."   
      
   Yet another recent study, conducted on a sample of about 100 inmates from a   
   correctional institution in the Southern United States, also determined that   
   MAOA is associated with higher rates of crime when the individual additionally   
   experienced childhood    
   adversity.   
      
   "These findings (published in the journal Psychiatric Genetics) indicate that   
   gene-by-environment interactions are important for understanding variation in   
   crime amongst populations with high base rates of criminal activity," said   
   principal investigator    
   Todd Armstrong of Sam Houston State University.   
      
   Tiihonen agrees that environmental factors, such as childhood abuse, are   
   important to consider. Also of relevance is, as Tiihonen said, "the mental   
   capacity to understand the nature and consequences of one's deeds, and ability   
   to control one's behavior."   
      
   He added that worldwide, about 20 percent of many populations carry at least   
   one of the two genetic variants. Clearly not all of these people are   
   murderers. Genetics is turning out to be a very important risk factor for   
   committing crime, but it's not the    
   only one.   
      
      
   http://news.discovery.com/human/genetics/murderers-may-be-hardwi   
   ed-to-kill-141028.htm   
      
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