Our genetic makeup may predispose us to certain personality traits orpatterns of behavior, a new UCLA study suggests. Variant forms of two keygenes, the DRD2 and DRD4 dopamine receptor genes, may play a role in causingand maintaining certain aggressive, impulsive personality types and reinforcingthe associated thrill-seeking behaviors. The study, led by Dr. Ernest Nobleof the UCLA School of Medicine, was published in the American Journal ofMedical Genetics.
Noble and colleagues previously demonstrated that the DRD2 gene linksto certain types of addictive and abusive behaviors such as alcohol abuse,drug abuse, smoking and overeating. Individuals who express these geneticvariants or alleles have fewer dopamine receptors in their brains to recordsensations of pleasure and satisfaction. These individuals may, therefore,be driven to overindulge in substances or activities that stimulate theirexisting receptors and give them pleasure levels comparable to people whohave a more standard number of pleasure receptors.
For the current study, the researchers evaluated 119 boys averaging12 years of age who had not yet used alcohol or other drugs of abuse. Eachsubject underwent a genetic screening and a standardized personality assessment(the Tridimensional Personality Questionnaire which measures three dimensionsof temperament).
The researchers found a marked correlation between behavior patternswhich they term "novelty seeking" and the expression of certainvariants of the DRD2 and DRD4 dopamine receptor genes. Novelty-seekingbehavior markers include excitability, impulsiveness, extravagance anddisorderliness.
"Identification of the molecular genetic factors contributing totemperament and personality is highly complicated, and we are just beginningto put the many pieces of this puzzle together," said Noble, PikeProfessor of Alcohol Studies and a professor of psychiatry and biobehavioralsciences at UCLA. "Despite the considerable evidence supporting therole of the dopamine receptor genes to pleasure and thrill-seeking behaviors,I believe as many as eight additional genes may be involved in formingand supporting personality characteristics."
According to Noble, certain personality characteristics are known tobe related to the body's dopaminergic system, as is predisposition to abusecertain substances. "Now we are making a link between the two,"he said. "People may be born with abusive tendencies, and these maybe detectable as personality traits well before they take their first drinkor puff of a cigarette. If we could predict who would become a substanceabuser, we could potentially provide early intervention that would helpthese individuals make appropriate and active choices about their lives.
"About half of an individual's personality relates to geneticsand half to environment including upbringing, education and the influenceof role models. But clearly, the genes we are born with are just as importantas the lessons our parents teach us," Noble added. "So thereis no clear slate at birth. The architecture for what we will become isalready in place well before we are born. Parents should only take partof the credit, and only part of the blame, for the kind of people theirchildren become."
Girls are just as likely as boys to demonstrate thrill-seeking behaviorsas a result of their genetic makeup, Noble stated. Subsequent studies willfollow children of both sexes in an effort to demonstrate the reliabilityof combined genetic screening and behavioral testing as predictive toolsfor addictive behavior.