Are personality disorders the outcomes of inherited traits? Are they brought on by abusive and traumatizing upbringing? Or, maybe they are the sad results of the confluence of both?

To identify the role of heredity, researchers have resorted to a few tactics: they studied the occurrence of similar psychopathologies in identical twins separated at birth, in twins and siblings who grew up in the same environment, and in relatives of patients (usually across a few generations of an extended family).

Tellingly, twins - both those raised apart and together - show the same correlation of personality traits, 0.5 (Bouchard, Lykken, McGue, Segal, and Tellegan, 1990). Even attitudes, values, and interests have been shown to be highly affected by genetic factors (Waller, Kojetin, Bouchard, Lykken, et al., 1990).

A review of the literature demonstrates that the genetic component in certain personality disorders (mainly the Antisocial and Schizotypal) is strong (Thapar and McGuffin, 1993). Nigg and Goldsmith found a connection in 1993 between the Schizoid and Paranoid personality disorders and schizophrenia.

The three authors of the Dimensional Assessment of Personality Pathology (Livesley, Jackson, and Schroeder) joined forces with Jang in 1993 to study whether 18 of the personality dimensions were heritable. They found that 40 to 60% of the recurrence of certain personality traits across generations can be explained by heredity: anxiousness, callousness, cognitive distortion, compulsivity, identity problems, oppositionality, rejection, restricted expression, social avoidance, stimulus seeking, and suspiciousness. Each and every one of these qualities is associated with a personality disorder. In a roundabout way, therefore, this study supports the hypothesis that personality disorders are hereditary.

This would go a long way towards explaining why in the same family, with the same set of parents and an identical emotional environment, some siblings grow to have personality disorders, while others are perfectly "normal". Surely, this indicates a genetic predisposition of some people to developing personality disorders.

Still, this oft-touted distinction between nature and nurture may be merely a question of semantics.

As I wrote in my book, "Malignant Self Love - Narcissism Revisited":

"When we are born, we are not much more than the sum of our genes and their manifestations. Our brain - a physical object - is the residence of mental health and its disorders. Mental illness cannot be explained without resorting to the body and, especially, to the brain. And our brain cannot be contemplated without considering our genes. Thus, any explanation of our mental life that leaves out our hereditary makeup and our neurophysiology is lacking. Such lacking theories are nothing but literary narratives. Psychoanalysis, for instance, is often accused of being divorced from corporeal reality.

Our genetic baggage makes us resemble a personal computer. We are an all-purpose, universal, machine. Subject to the right programming (conditioning, socialization, education, upbringing) - we can turn out to be anything and everything. A computer can imitate any other kind of discrete machine, given the right software. It can play music, screen movies, calculate, print, paint. Compare this to a television set - it is constructed and expected to do one, and only one, thing. It has a single purpose and a unitary function. We, humans, are more like computers than like television sets.

True, single genes rarely account for any behavior or trait. An array of coordinated genes is required to explain even the minutest human phenomenon. "Discoveries" of a "gambling gene" here and an "aggression gene" there are derided by the more serious and less publicity-prone scholars. Yet, it would seem that even complex behaviors such as risk taking, reckless driving, and compulsive shopping have genetic underpinnings."

Read More

Liveslye, W.J., Jank, K.L., Jackson, B.N., Vernon, P.A.. 1993. Genetic and environmental contributions to dimensions of personality disorders. Am. J. Psychiatry. 150(O12):1826-31.