It was commonly held that the personality disorders reflected the warping effect of adverse early social environment. Now there is mounting evidence that personality is, in great measure, biologically determined. Both genetic and constitutional (i.e., intrauterine and early physical developmental) factors may be important.
Although not all personality disorders have been examined, for the majority there is a severalfold increase in concordance between monozygotic twins compared with dizygotic twins.
Some of the most careful work has been with antisocial personality. Here it is noted that prevalence among men is three- to fourfold higher than in women, and that first-degree relatives of persons diagnosed as antisocial show increased prevalence of antisocial personality, alcoholism, and somatization disorder (Briquet’s syndrome). The latter is characterized by intractable multiorgan system complaints in women who often have a histrionic personality. The association of these two disorders in the same pedigrees has led to suggestions that Briquet’s syndrome and antisocial disorder are expressions in women and men of a common biogenetic substrate.
The operation of genetic factors in antisocial personality is further demonstrated by the finding that biologic offspring of antisocial and alcoholic parents have a higher risk of developing antisocial personality disorder even if they are raised by adoptive parents who do not have any antisocial traits. The converse has also been demonstrated: children adopted by antisocial parents tend not to develop antisocial disorder themselves unless they have antisocial personality or alcoholism in their blood relatives.
The XYY chromosomal abnormality was once thought to be related to antisocial personality disorder. More recent studies indicate that although XYY might be overrepresented in certain prison populations, the vast majority of XYY men are not antisocial.
The schizotypal, borderline, and schizoid diagnoses evolved orginally from the notion that there ought to be a “preclinical” form of schizophrenia characterized by lesser severity or fewer numbers of the cognitive and interpersonal symptons of that disorder. Thus, the schizotypal personality might, theoretically, embody earlier forms of the disturbance in thinking, perception, and attention that occur in schizophrenia; whereas the schizoid personality would represent the interpersonal awkwardness inherent in that disorder. Genetic studies have confirmed that there is some increase in schizotypal (but not schizoid) personality in relatives of diagnosed schizophrenics.
The borderline personality is genetically heterogeneous. Up to 50 percent of borderline patients have a family history of affective disorder. Borderline disorder itself, as well as other personality disorders, are also more common in first-degree relatives of borderline patients, but schizophrenia is not consistently related.
There is increased schizophrenia in the families of patients with paranoid personality. For compulsive disorder, twin studies indicate increased concordance for obsessional traits in monozygotic versus dizygotic twins. There is also some evidence that orderliness and rigidity run in families.
The other personality disorders have not been studied carefully from a biogenetic standpoint.
Although there is good evidence that infants are born with certain temperamental characteristics (e.g., high versus low activity level; long versus short attention span), there is little evidence that these temperamental characteristics persist into adolescence. Infant temperament does not appear to predict later personality disorder with the exception that the “difficult child” (irritable, hard to console, irregular rhythms) tends to exhibit more behavioral disturbances. Low intelligence quotient and poor physical health as a child have been noted more frequently in the histories of persons with personality disorders.
Neurophysiologic and neuroendocrine correlates
Several ncuro-physiologic and biochemical changes may be associated with personality disorders. Abnormal slow waves and spikes have been reported in the EEGs of antisocial persons. For borderline patients, patterns suggestive of periodic limbic epileptiform discharges have sometimes been noted.
Some observers suggest that a common neurophysiologic feature of both antisocial and hysterical disorders is reduced cortical arousal to cortical stimulation, secondary to increased inhibition from lower brain regions. This may be coupled with motor disinhibition in antisocial persons and autonomic disinhibition in hysterics.
The schizotypal personality disorder has been associated with disturbance in smooth pursuit eye movement (SPEM). Since many schizophrenics are also poor trackers, it may be that schizotypals share with schizophrenics decreased neural effectiveness in “centering.” Some schizophrenics and schizotypals have lowered platelet monoamine oxidase (MAO) levels. It has been suggested that lowered MAO activity could be related to inefficient degradation of certain biologically active amines, leading to accumulation of substance with psychotomimetic properties.
Cortisol escape from dexamethasone suppression and shortened rapid eye movement (REM) latency (REM latency is the time between falling asleep and first REM episode) are associated with affective disorder. Both phenomena have also been observed in borderline and obsessive-compulsive personalities, suggesting a link among the affective, borderline, and obsessive-compulsive disorders.
There are no specific data on biologic correlates of the other personality disorders.
Early social environment has proved to be an inconsistent predictor of late personality disorder. For example, one study found that 30 percent of men with personality disorders who were investigated reported lack of maternal warmth as children, but so did 24 percent of controls. Multiple problems in the early environment were found in 16 percent of personality-disordered men and 10 percent of those without disorders. Being abused as a child is associated with violence in later life.
The relative weakness of both temperamental and environmental factors as predictors of future personality disorder has led to a “goodness of fit” hypothesis. This theory suggests that later behavioral disorders are more likely when there is a severe mismatch between a child’s temperament and childrearing practices and environmental circumstances.