• Violence and personality disorders: clinical and forensic implications (2010)

  1) most of those suffering from PD (Personality Disorders) are not violent and never have been;
  2) many abnormal personalities are more likely to be victims then criminals
  3) no PD is necessarily associated to violent behavior permanently, and
  4) from a dynamic and motivational position, PD alone cannot explain violent behavior.

  The article is also helpful in discussing each type of personality disorder in the context of violent acts. In all, there are 10 personality disorders plus one unspecified. They are: Paranoid personality disorder (PPD); Schizoid personality disorder (SPD); Schizotypal personality disorder (STPD); Antisocial personality disorder (ASPD)/Psychopathy; Borderline personality disorder (BPD); Narcissistic personality disorder (NPD); Histrionic personality disorder (HPD); Obsessive-compulsive personality disorder (OCPD); Dependent personality disorder (DPD); Anxious-avoidant personality disorder (AAPD; Unspecified personality disorder (USPD)(includes sadistic personality disorder.)

  There are 6 types of personality disorders more prone to violent behaviors: antisocial, borderline, paranoiac, narcissistic, and to a lesser degree, dependent and anxious-avoidant.

• Physician's Desk Reference: Personality Disorders

  Explains each type of personality disorder, and gives symptoms, risk factors, causes, and treatment for each, in language that is easy to understand (compared to the scientific journals.)

  Personality disorder is a major risk factor for attempted and completed suicides, as well as self-mutilation....Persons with borderline personality disorders have a higher risk for self-mutilation or cutting themselves. People may slash themselves to release built-up tension, to get attention, to punish themselves, or for symbolic reasons. Mutilation is most often seen during a time of perceived or actual loss, and is more often due to anger than depression.

  Also:

  Many personality disorders run in families; however, whether this occurs as a result of genetics or learned behavior is still a subject of debate. Gender plays a role in one's likelihood of having a particular personality disorder. Certain personality disorders (such as antisocial personality disorder) are more frequent in males, whereas others (such as borderline, histrionic, and dependent personality disorders) are seen more often in women.

  Causation:

  Little is understood about the causes of personality disorders. Some disorders may be inheritable. Temperamental factors in childhood may also be associated with personality disorders as an adult. Certain personality disorders may occur because of temperamental differences between a child and the parents. Education, moral teachings, life experiences, and adolescent socialization may also play a role. None of these possibilities, however, have been proven in scientific studies. Other factors such as physical, verbal, and sexual abuse, neglect, loss or separation during childhood, and brain abnormalities have also been cited as possible causes for personality disorders.

  Although most personality disorders appear during the teenage years, others can appear later in life as a result of physical damage to the brain, psychiatric illness, or extreme stress.

  Treatment Prognosis:

  The prognosis is best for patients with borderline personality disorder, obsessive-compulsive personality disorder, dependent personality disorder, and avoidant personality disorder. The prognosis is worse for antisocial personality disorder, paranoid personality disorder, schizoid personality disorder, and schizotypal personality disorder.

• Is Schizoid Personality a Forerunner of Homicidal or Suicidal Behavior? (2006)

  The crucial distinguishing features of schizoid personality disorder...are that the person appears to have a defect in the capacity to form social relationships and consequently is emotionally cold, aloof, or detached; has flattened affectivity; lacks close friends or confidants other than first degree family relatives; has little, if any, interest in having a sexual experience with another person; takes pleasure in few if any activities; and almost always chooses solitary activities....People with schizoid personality disorder are predisposed to develop brief psychotic episodes.

  ...[Character traits are ]inability to form social and intimate relationships, inability to appropriately respond to social cues, depression, restricted range of emotions, disintegration of self based on incorrectly perceived threats or criticism, a drive to destroy themselves and others, and the difference between what occurs in the inner world and that which one displays in the outward appearance).
  

On genetic links: Most experts agree the search for a gene to predict violence or even severe mental illness is likely to be futile. Many argue it is a slippery slope, and one that could lead to unfair stigmatization.

"It is almost inconceivable that there is a common genetic factor’’ to be found in mass murders, said Dr. Robert C. Green, a geneticist and neurologist at Harvard Medical School. ‘‘I think it says more about us that we wish there was something like this. We wish there was an explanation."

Is a family history that includes suicide or depression relevant to anything? Most experts agree they are not indicators of violence.

On heredity and mental illness, Web MD says:

Many mental illnesses run in families, suggesting that people who have a family member with a mental illness are more likely to develop one themselves. Susceptibility is passed on in families through genes. Experts believe many mental illnesses are linked to abnormalities in many genes -- not just one. That is why a person inherits a susceptibility to a mental illness and doesn't necessarily develop the illness. Mental illness itself occurs from the interaction of multiple genes and other factors --such as stress, abuse, or a traumatic event -- which can influence, or trigger, an illness in a person who has an inherited susceptibility to it.

Similar here (on bi-polar disorder); here (schizophrenia and bipolar disorder); here and here.

On genetic testing and mental illness, here's a fact sheet from the National Institute of Mental Health.

On a genetic link to suicide -- more here.

None of these materials will tell us anything about Adam Lanza, particularly since we don't know whether he had a personality disorder or mental illness. And even if he did, it's still likely most people with that disorder don't commit violent acts.

I don't think anyone will ever know why Adam Lanza did what he did. The one person who knew him best, his mother, is gone. Even if he had a mental illness or personality disorder, it's unfair to stigmatize all people with that disorder, since so few of them commit violent acts.

Feel free to comment, but keep your comments on topic, which means no discussion of gun laws in this thread. Comments about gun control will be deleted. There are other threads, and open threads for that.