The roots of personality features such as boldness and timidity, novelty seeking and excitability, level of energy and motor activity, fearfulness and fearlessness, social adaptability and rigidity or stubbornness are already evident in the first months of life. Monozygotic twins are alike (but not absolutely identical) in these respects, even when reared apart. Gesell and his colleagues, in their studies of infants in the middle of the last century (see Chap. 27), observed individual differences that are clearly innate; each of these characteristics is likely to be genetically determined, like intelligence. The personalities that result are as individualistic as fingerprints. One example of a biologic and genetic basis of a human personality trait, albeit to a limited degree, has been found in the expression of thrill seeking, exploration, and excitability. For example, according to the early work of Cloninger and colleagues (1996), polymorphisms of a dopamine receptor gene accounts in small measure for the genetic variability of this personality type. Findings such as these have been reproduced for similar polymorphisms that contribute to the traits of timidity, anxiety, and obsessiveness. The notion, expressed by authors such as Kandel, that genetics will explain a large part of mental function and mental illness sounds reasonable enough, but the data to establish this are far from complete.
The interesting and related construct of a “national character” is embedded in social discourse but has not been extensively studied. It is mentioned here to allow for a more complete picture of the concept of character. A survey by Terracciano and colleagues indicates that mean personality traits in 49 cultures do not correspond to general stereotypes and are therefore probably simply contrivances for maintaining national identity. Similar comments can be proffered regarding sex differences in personality that are embedded in cultural stereotypes but these latter personality profiles have more data to suggest a degree of uniformity and validity in differences between men and women in all cultures.
An unsolved problem is whether each of the personality types accepted by the American Psychiatric Association is predictive or determinative of a later mental disorder. In this regard, 2 broad groups of personality disorders can be recognized. In one group—comprising the paranoid, schizoid, cyclothymic, and obsessive-compulsive personality types—there are obvious similarities to major types of psychiatric illness. Thus, among patients who develop paranoid schizophrenia, a considerable number will have had the attributes described under “paranoid personality type.” Similarly, among patients who develop schizophrenia of another type, the history will frequently disclose a preexistent “schizoid” personality. In fact, it may be difficult to judge where the personality disorder leaves off and the schizophrenic illness began. Similarly, it seems clear from several family studies that the cyclothymic personality is related to bipolar disease. Obsessive-compulsive personality is related not only to obsessive-compulsive neurosis, as one might expect, but also to depressive disease. The notion of clusters of personality traits has been introduced and may be more useful in clinical work than are the discrete personality types (see Tyrer).
Perhaps most problematic in classification but seen regularly in medical practice is the “borderline personality disorder.” As with other personality types, the pattern of behaviors is pervasive and lifelong in the affected individual. An ensemble of poorly regulated emotions, impulsive and aggressive actions, and repeated self-injury form the core aspects of the disorder. These patients typically express a range of profound emotional “pains” and a sense of dysphoria, often rapidly changing from one mood to another without provocation. There may be additional nonpsychotic problems that border on paranoia with feelings of low self-esteem. Interpersonal relationships are made unstable as a result of fear of being left alone combined with argumentativeness. These are among the most distressing individuals for families and physicians to deal with and little success has been achieved in treatment. The potential biologic roots of the borderline personality disorder were reviewed by Lieb and colleagues and the clinical features, by Gunderson, who emphasizes the difficulties in treating these people, currently limited mainly to various types of insight-oriented psychotherapies.