THURSDAY, May 23 (HealthDay News) -- Symptoms of borderline personality disorder often mimic traits of other psychiatric disorders, complicating diagnosis and treatment. But researchers in Canada say they have identified a characteristic that may be unique to borderline personality disorder: a tendency to misinterpret emotions expressed by the face. "They have difficulty processing facial emotions and will see a negative emotion on a neutral face," said Anthony Ruocco, a clinical neuropsychologist and assistant professor at the University of Toronto. "This is not seen in bipolar disorder or schizophrenia." Inaccuracies in recognizing anger, sadness, fear and disgust also were noted in Ruocco's recent study, with greater deficits related to anger and disgust. Although more research is needed to understand the brain mechanisms involved in these misperceptions and their significance, Ruocco called these "potentially important" deficits. "There may be neurobiological factors that contribute to these biases in emotion perception," he said. Pinpointing those factors might lead to better understanding of the illness and improved treatments. But whether these misperceptions trigger the outbursts so common among people with borderline personality disorder was not within the scope of the studies. People with borderline personality disorder have trouble regulating their emotions. They tend to act impulsively, lash out in anger and have stormy relationships. Many fear abandonment, complain of feeling empty and engage in bodily self-harm, such as cutting. High rates of suicide also are associated with the condition. Ruocco discussed the study, published in the journal Psychological Medicine, at recent conferences co-sponsored by the National Education Alliance for Borderline Personality Disorder in Boston and New Haven, Conn. His research, called a meta-analysis, involved a review of 10 previously published studies on emotion recognition. More than 500 people were involved: 266 with borderline personality disorder and 255 mentally healthy people, or controls. Participants were overwhelmingly female, with an average age of 29. Not only did subjects with borderline personality disorder misread facial emotions, the studies showed, but they also took more time to interpret facial emotions than others. And when they perceived anger, it induced stronger reactions than in healthy control subjects, Ruocco's team found. Two of the studies analyzed noted that patients were more likely to report negative emotions when viewing faces displaying no emotion. "Neutral faces are simply faces that were produced by actors with the intention of showing no emotion," Ruocco said. "Typically, researchers have tested these faces with healthy individuals and confirmed that nearly all people perceive them as neutral." A smaller study conducted by Ruocco's team, which is not yet published, found that individuals with borderline personality disorder also reported mild expressions of sadness as more intensely sad than others do. This was true even when the researchers accounted for depression. About 6 percent of adults in the United States have borderline personality disorder, according to the National Education Alliance for Borderline Personality Disorder, which also estimates that 20 percent of all psychiatric hospital admissions and 10 percent of outpatient treatment involve the condition. More information The National Education Alliance for Borderline Personality Disorder has more about borderline personality disorder.