Academic journal article Canadian Psychology

Clinical Implications of Biological Factors in Personality Disorders

Academic journal article Canadian Psychology

Clinical Implications of Biological Factors in Personality Disorders

Article excerpt

All mental disorders have neural correlates, and personality disorder (PD) is no exception. All mental disorders are also associated with heritable risk factors that play a role in their etiology (for a review, see Jang, 2005). Behaviour genetic methods compare concordance rates in monozygotic and dizygotic twins, allowing for quantitative estimates of heritability. They show that genes account for about half the variance in personality traits, as well as in PDs (Plomin, DeFries, Knopik, & Neiderhiser, 2012).

The heritability of PDs has been demonstrated by large scale behaviour genetic studies (Reichborn-Kjennerud, 2010; Torgersen et al., 2002; Torgersen et al., 2012). Thus, borderline personality disorder, for example, which was long thought to be an environmental condition, has a single heritable factor that accounts for 55% of the variance in all nine of its DSM-5 criteria (Reichborn-Kjennerud et al., 2013). These studies also showed that the level of genetic influence is in much the same range as for personality traits. The precise nature of these heritable factors remains unknown.

These findings confirm that PD is not a simple, direct consequence of bad parenting or child abuse, but is rooted in interactions between an abnormal temperament and an adverse environment. Even when a disorder is heritable, it does not necessarily develop unless environmental stressors are also present (e.g., Rutter, 2006). Thus, the effects of biology always have to be understood in the light of their interactions with a psychosocial context: Genes "bend the twig," but do not determine the shape of the tree.

Genetic influences can also be measured by temperament, defined as the heritable aspect of personality, present a birth, which is then shaped by experience into stable traits, and can be amplified to pathological levels by psychosocial adversity (see Rutter, 1987). A vulnerable temperament tends to make the development of a PD more likely, and determines the type of PD that can develop. This principle applies to all PDs: For example, highly introverted people will rarely develop narcissistic PD, and a highly extraverted person would not develop avoidant PD (Paris, 2003).

Some of the most important effects of heritable factors in psychopathology lie in individual differences in susceptibility to environmental risks. People who are highly resilient can be surprisingly unaffected by serious life adversities (Rutter, 2012). Others, who are highly sensitive, will be affected by all kinds of life events, both good and bad, which can be either an adaptive or maladaptive trait, depending on the context (Belsky & Pruess, 2013).

Biomarkers in medicine help to make diagnosis precise, can be useful in research, and might be applied to identify high-risk populations. Yet at this point, no markers for any type of PD have been discovered. Actually, no biomarkers for any major mental disorder are known at the present time (Hyman, 2010). Potential biomarkers for PD could be identified by abnormalities in gene sequences, in neurotransmission, in neuropsychological measures, or in neuroimaging, that is, the volume, activity, and connectivity of specific brain areas (New et al., 2007). A large body of research has used each of these approaches. Most of the research has focused on borderline personality disorder (BPD), although there is a smaller literature on antisocial PD (Raine, 2013) and schizotypal PD (Chemerinski, Triebwasser, Roussos, Siever, & Peters, 2013).

The state of current knowledge about biological markers for PDs can be summaris(ed) as follows:

1. No specific allele has been found that can account for any PD. A few studies have examined genetic variations in BPD, but they account for no more than 1% of the variance (Ni, Chan, Chan, McMain, & Kennedy, 2009). It is likely that the heritability of PDs, as is the case for other mental disorders (Kendler, 2013), is associated with a large number of interacting genes with small effects that are also under epigenetic control. …

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