Rep36 Understanding Personality Disorder

2.2.1 Biological factors in personality
disorder
2.2.1a Genetic factors
Studies looking at genetic factors have examined
either the heritability of normal personality traits
and concentrated upon dimensional and
psychobiological models of personality, or they
have studied the heritability of pathological
personality and concentrated upon categorical
models of personality. The studies concentrating
upon the heritability of normal personality have
drawn information from a variety of dimensional
models (Livesley, 2001). Using data from twin
and adoption studies, there is evidence to
suggest that personality dimensions are highly
heritable, with an inherited component of 40 to
50 per cent (Paris, 1996). Other studies have
shown that attributes such as callousness, identity
problems, narcissism and oppositionality are
highly heritable, whereas social closeness, self-
harm and submissiveness are only moderately
heritable (Paris, 1996). The psychobiological
models focus on evolutionary determined
behavioural adaptations that are perceived to
result in heritable temperamental traits, that is,
novelty seeking, harm avoidance, reward
dependence and persistence, which shape
personality development (Cloninger 
et al
., 1993).
Studies concentrating upon the heritability of
personality disorder have suggested three causal
mechanisms in the development of personality
disorder. First, it has been found that antisocial
personality, borderline personality and substance
abuse frequently occur together in family
studies, resulting in the hypothesis that they
form a group of impulsive spectrum disorders
associated with a common temperament
(Zanarini, 1993). Second, individuals with
schizoid, paranoid and schizotypal personality
disorders tend to have relatives with
schizophrenia or schizophrenia spectrum
disorders (Paris, 1996). Third, individuals with
avoidant, dependent and compulsive personality
disorders tend to have relatives with anxiety
disorders (Paris, 1996).