One’s personality develops from a complex and dynamic interplay between nature (i.e. genetics) and nurture (i.e. environment). Typically, personality traits remain relatively stable throughout adulthood.

Nonetheless, we organize personality disorders into three “Clusters” (i.e., Cluster A, Cluster B, and Cluster C) with each cluster sharing similar core features. 

Schizoid Personality Disorder
A pervasive pattern of detachment from social relationships and a restricted range of expression of emotions in interpersonal settings.  Need 4 out of 7:
1. Patient neither desires nor enjoys close relationships, including being part of a family;
2. Patient almost always chooses solitary activities;
3. Patient has little, if any, interest in having sexual experiences with others;
4. Patient takes pleasure in few, if any, activities;
5. Patient lacks close friends or confidants, other than first degree relatives;
6. Patient appears indifferent to the praise or criticism of others;
7. Patient is emotionally cold, detached, or with flattened affectivity.

Schizotypal Personality Disorder
A pervasive pattern of social and interpersonal deficits, marked by acute discomfort with, and reduced capacity for close relationships as well as cognitive or perceptual distortions and eccentricities of behavior.  Need 5 out of 9:
1. Ideas of reference (excluding delusions of reference);
2. Odd beliefs or magical thinking that influences behavior and is inconsistent with subcultural norms (superstitiousness, belief in clairvoyance, telepathy, or 6th sense);
3. Unusual perceptual experiences, including bodily illusions;
4. Odd thinking and speech (vague, circumstantial, metaphorical, over-elaborate, or stereotyped);
5. Suspiciousness or paranoid ideation;
6. Inappropriate or constricted affect;
7. Odd, eccentric, peculiar behavior or appearance;
8. Lacks close friends or confidants, other than first degree relatives;
9. Excessive social anxiety that does not diminish with familiarity, and tends to be associated with paranoid fears rather than negative judgments about self.

Borderline Personality Disorder
A pervasive pattern of instability of interpersonal relationships, self-image, and affect, and marked impulsivity.  Need 5 out of 9:
1. Frantic efforts to avoid real or imagined abandonment;
2. A pattern of unstable and intense interpersonal relationships characterized by changing between extremes of idealization and devaluation;
3. Identity disturbance:  Markedly unstable self image sense of self;
4. Impulsivity in at least two areas that are self damaging (spending, sex, substance abuse, reckless driving, binge eating);
5. Recurrent suicidal behavior/gestures/threats; or self-mutilating behavior;
6. Affective instability due to marked reactivity of mood (intense episodic dysphoria, irritability, or anxiety lasting a few hours);
7. Chronic feelings of emptiness;
8. Inappropriate, intense anger or difficulty controlling anger;
9. Transient stress-related paranoid ideation, or severe dissociative symptoms.

Narcissistic Personality Disorder
A pervasive pattern of grandiosity (in fantasy or behavior), need for admiration, and lack of empathy.  Need 5 out of 9:
1. Grandiose sense of self-importance (exaggerates achievements);
2. Preoccupied with fantasies of unlimited success, power, brilliance, beauty;
3. Believes she is special/unique, and can only be understood by or should only associate with other special or high status people (or institutions);
4. Requires excessive admiration;
5. Has sense of entitlement, expectation of favorable treatment;
6. Is interpersonally exploitative;
7. Lacks empathy, unwilling to recognize feelings/needs of others;
8. Is envious of others and believes others are envious of her;
9. Shows arrogant, haughty behaviors or attitudes.

Histrionic Personality Disorder
A pervasive pattern of excessive emotionality and attention seeking.  5 out of 8:
1. Patient is uncomfortable when he is not the center of attention;
2. Interaction with others often characterized by inappropriate sexually seductive/provocative behaviors;
3. Patient displays rapidly shifting and shallow expression of emotions;
4. Patient consistently uses physical appearance to draw attention to self;
5. Patient’s style of speech is overly impressionistic and lacking in detail;
6. Shows self-dramatization/theatricality/exaggerated expression of emotion;
7. Patient is suggestible, easily influenced by others or circumstances;
8. Patient considers relationships to be more intimate than they actually are.

Avoidant Personality Disorder
A pervasive pattern of social inhibition, feelings of inadequacy, and hypersensitivity to negative evaluation. Need 4 out of 7:
1. Avoids work that involves significant interpersonal contact, because of fears of criticism, disapproval, or rejection;
2. Is unwilling to get involved with people unless certain of being liked;
3. Shows restraint with intimate relationships because of fears of being shamed or ridiculed;
4. Is preoccupied with being criticized or rejected in social situations;
5. Is inhibited in new social situations because of feelings of inadequacy;
6. Views self as socially inept, personally unappealing, or inferior;
7. Is reluctant to take personal risks or engage in new activities because they may prove embarrassing.

Dependent Personality Disorder
A pervasive and excessive need to be taken care of that leads to submissive and clinging behavior and fear of separation.  Need 5 out of 8:
1. Difficulty making every day decisions without excessive advice and reassurance from others;
2. Needs others to assume responsibility for most major areas of life;
3. Has difficulty expressing disagreement because of fear of loss of support or approval;
4. Has difficulty initiating projects or doing things on her own (because of lack of self confidence rather than lack of motivation);
5. Goes to excessive lengths to obtain nurturance/support from others, to the point of volunteering to do unpleasant things;
6. Feels uncomfortable or helpless when alone because of exaggerated fears that she cannot care for self;
7. Urgently seeks new relationships as a source of care/support when a close relationship ends;
8. Is unrealistically preoccupied with fears of being left to care for self.

Obsessive-Compulsive Personality Disorder
A pervasive pattern of preoccupation w orderliness, perfectionism, and mental and interpersonal control, at the expense of flexibility, openness, and efficiency. 4 out of 8:
1. Preoccupied with details, rules, lists, order, organization, or schedules to the extent that the major point of the activity is lost;
2. Shows perfectionism that interferes with task completion;
3. Excessively devoted to work and productivity to the exclusion of leisure activities and friendships;
4. Over-conscientious, scrupulous, and inflexible about matters of morality/ethics/values;
5. Unable to discard worn-out or worthless objects even when they have no sentimental value;
6. Reluctant to delegate tasks or to work with others unless they submit exactly to his or her way of doing things;
7. Adopts miserly spending style towards self and others;  money viewed as something to be hoarded for future catastrophes;
8. Shows rigidity and stubbornness.

In general, each personality disorder has a prevalence of approximately 1%. Personality disorders are very difficult to treat as they require changing ingrained patterns of behavior. Therefore, psychotherapy and group therapy remain the primary treatments for managing personality disorders.

Schizotypal Personality Disorder and Schizoid Personality Disorder: These personality disorders commonly occur in families with history of Psychotic disorders. This tells us that there are likely genetic links between primary psychotic disorders and cluster A personality disorders. Some experts would argue that Schizotypal and Schizoid personality disorders are part of a spectrum including schizophrenia and related psychotic disorders.

Histrionic Personality Disorder: The most common defense mechanism used by individuals with histrionic personality disorder is “regression.”