Complications of late Parkinson's disease may include a range of impulse-control disorders, including eating, buying, compulsive gambling and sexual behavior. One study found that 13.6% of Parkinson's patients exhibited at least one form of ICD. There is a significant co-occurrence of pathological gambling and personality disorder, and is suggested to be caused partly by their common "genetic vulnerability". The degree of heritability to ICD is similar to other psychiatric disorders including substance abuse disorder. There has also been found a genetic factor to the development of ICD just as there is for substance abuse disorder. The risk for subclinical PG in a population is accounted for by the risk of alcohol dependence by about 12-20% genetic and 3-8% environmental factors. There is a high rate of comorbidity between ADHD and other impulse-control disorders.

Kleptomania is characterized by an impulsive urge to steal purely for the sake of gratification.

In the U.S. the presence of kleptomania is unknown but has been estimated at 6 per 1000 individuals. Kleptomania is also thought to be the cause of 5% of annual shoplifting in the U.S. If true, 100,000 arrests are made in the U.S. annually due to kleptomaniac behavior.

Dependent personality disorder occurs in about 0.6% of the general population. The disorder is diagnosed more often in females than males; however, research suggests that this is largely due to behavioural differences in interviews and self-reporting rather than a difference in prevalence between the sexes. A 2004 twin study suggests a heritability of 0.81 for developing dependent personality disorder. Because of this, there is significant evidence that this disorder runs in families. Children and adolescents with a history of anxiety disorders and physical illnesses are more susceptible to acquiring this disorder.

Epidemiological data are limited, but reactive attachment disorder appears to be very uncommon. The prevalence of RAD is unclear but it is probably quite rare, other than in populations of children being reared in the most extreme, deprived settings such as some orphanages. There is little systematically gathered epidemiologic information on RAD. A cohort study of 211 Copenhagen children to the age of 18 months found a prevalence of 0.9%.

Attachment disorders tend to occur in a definable set of contexts such as within some types of institutions, in the presence of repeated changes of primary caregiver or of extremely neglectful identifiable primary caregivers who show persistent disregard for the child's basic attachment needs, but not all children raised in these conditions develop an attachment disorder. Studies undertaken on children from Eastern European orphanages from the mid-1990s showed significantly higher levels of both forms of RAD and of insecure patterns of attachment in the institutionalized children, regardless of how long they had been there. It would appear that children in institutions like these are unable to form selective attachments to their caregivers. The difference between the institutionalized children and the control group had lessened in the follow-up study three years later, although the institutionalized children continued to show significantly higher levels of indiscriminate friendliness. However, even among children raised in the most deprived institutional conditions the majority did not show symptoms of this disorder.

A 2002 study of children in residential nurseries in Bucharest, in which the DAI was used, challenged the current DSM and ICD conceptualizations of disordered attachment and showed that inhibited and disinhibited disorders could coexist in the same child.

There are two studies on the incidence of RAD relating to high risk and maltreated children in the U.S. Both used ICD, DSM and the DAI. The first, in 2004, reported that children from the maltreatment sample were significantly more likely to meet criteria for one or more attachment disorders than children from the other groups, however this was mainly the proposed new classification of disrupted attachment disorder rather than the DSM or ICD classified RAD or DAD. The second study, also in 2004, attempted to ascertain the prevalence of RAD and whether it could be reliably identified in "maltreated" rather than "neglected" toddlers. Of the 94 maltreated toddlers in foster care, 35% were identified as having ICD RAD and 22% as having ICD DAD, and 38% fulfilled the DSM criteria for RAD. This study found that RAD could be reliably identified and also that the inhibited and disinhibited forms were not independent. However, there are some methodological concerns with this study. A number of the children identified as fulfilling the criteria for RAD did in fact have a preferred attachment figure.

It has been suggested by some within the field of attachment therapy that RAD may be quite prevalent because severe child maltreatment, which is known to increase risk for RAD, is prevalent and because children who are severely abused may exhibit behaviors similar to RAD behaviors. The APSAC Taskforce consider this inference to be flawed and questionable. Severely abused children may exhibit similar behaviors to RAD behaviors but there are several far more common and demonstrably treatable diagnoses which may better account for these difficulties. Further, many children experience severe maltreatment and do not develop clinical disorders. Resilience is a common and normal human characteristic. RAD does not underlie all or even most of the behavioral and emotional problems seen in foster children, adoptive children, or children who are maltreated and rates of child abuse and/or neglect or problem behaviors are not a benchmark for estimates of RAD.

There are few data on comorbid conditions, but there are some conditions that arise in the same circumstances in which RAD arises, such as institutionalization or maltreatment. These are principally developmental delays and language disorders associated with neglect. Conduct disorders, oppositional defiant disorder, anxiety disorders, post-traumatic stress disorder and social phobia share many symptoms and are often comorbid with or confused with RAD. Attachment disorder behaviors amongst institutionalized children are correlated with attentional and conduct problems and cognitive levels but nonetheless appear to index a distinct set of symptoms and behaviors.

Dependent personality disorder (DPD), formerly known as asthenic personality disorder, is a personality disorder that is characterized by a pervasive psychological dependence on other people. This personality disorder is a long-term condition in which people depend on others to meet their emotional and physical needs, with only a minority achieving normal levels of independence.

The cause of dependent personality disorder is unknown. A study in 2012 estimated that between 55% and 72% of the risk of the condition is inherited from one's parents. The difference between a "dependent personality" and a "dependent personality disorder" is somewhat subjective, which makes diagnosis sensitive to cultural influences such as gender role expectations.

The AACAP guidelines state that children with reactive attachment disorder are presumed to have grossly disturbed internal models for relating to others. However, the course of RAD is not well studied and there have been few efforts to examine symptom patterns over time. The few existing longitudinal studies (dealing with developmental change with age over a period of time) involve only children from poorly run Eastern European institutions.

Findings from the studies of children from Eastern European orphanages indicate that persistence of the inhibited pattern of RAD is rare in children adopted out of institutions into normative care-giving environments. However, there is a close association between duration of deprivation and severity of attachment disorder behaviors. The quality of attachments that these children form with subsequent care-givers may be compromised, but they probably no longer meet criteria for inhibited RAD. The same group of studies suggests that a minority of adopted, institutionalized children exhibit persistent indiscriminate sociability even after more normative caregiving environments are provided. Indiscriminate sociability may persist for years, even among children who subsequently exhibit preferred attachment to their new caregivers. Some exhibit hyperactivity and attention problems as well as difficulties in peer relationships. In the only longitudinal study that has followed children with indiscriminate behavior into adolescence, these children were significantly more likely to exhibit poor peer relationships.

Studies of children who were reared in institutions have suggested that they are inattentive and overactive, no matter what quality of care they received. In one investigation, some institution-reared boys were reported to be inattentive, overactive, and markedly unselective in their social relationships, while girls, foster-reared children, and some institution-reared children were not. It is not yet clear whether these behaviors should be considered as part of disordered attachment.

There is one case study on maltreated twins published in 1999 with a follow-up in 2006. This study assessed the twins between the ages of 19 and 36 months, during which time they suffered multiple moves and placements. The paper explores the similarities, differences and comorbidity of RAD, disorganized attachment and post traumatic stress disorder. The girl showed signs of the inhibited form of RAD while the boy showed signs of the indiscriminate form. It was noted that the diagnosis of RAD ameliorated with better care but symptoms of post traumatic stress disorder and signs of disorganized attachment came and went as the infants progressed through multiple placement changes. At age three, some lasting relationship disturbance was evident.

In the follow-up case study when the twins were aged three and eight years, the lack of longitudinal research on maltreated as opposed to institutionalized children was again highlighted. The girl's symptoms of disorganized attachment had developed into controlling behaviors—a well-documented outcome. The boy still exhibited self-endangering behaviors, not within RAD criteria but possibly within "secure base distortion", (where the child has a preferred familiar caregiver, but the relationship is such that the child cannot use the adult for safety while gradually exploring the environment). At age eight the children were assessed with a variety of measures including those designed to access representational systems, or the child's "internal working models". The twins' symptoms were indicative of different trajectories. The girl showed externalizing symptoms (particularly deceit), contradictory reports of current functioning, chaotic personal narratives, struggles with friendships, and emotional disengagement with her caregiver, resulting in a clinical picture described as "quite concerning". The boy still evidenced self-endangering behaviors as well as avoidance in relationships and emotional expression, separation anxiety and impulsivity and attention difficulties. It was apparent that life stressors had impacted each child differently. The narrative measures used were considered helpful in tracking how early attachment disruption is associated with later expectations about relationships.

One paper using questionnaires found that children aged three to six, diagnosed with RAD, scored lower on empathy but higher on self-monitoring (regulating your behavior to "look good"). These differences were especially pronounced based on ratings by parents, and suggested that children with RAD may systematically report their personality traits in overly positive ways. Their scores also indicated considerably more behavioral problems than scores of the control children.

The cause of BFRBs is unknown.

Emotional variables may have a differential impact on the expression of BFRBs.

Research has suggested that the urge to repetitive self-injury is similar to a body-focused repetitive behavior but others have argued that for some the condition is more akin to a substance abuse disorder.

Researchers are investigating a possible genetic component.

Somatization disorder is estimated to occur in 0.2% to 2% of females, and 0.2% of males.

There are cultural differences in the prevalence of somatization disorder. For example, somatization disorder and symptoms were found to be significantly more common in Puerto Rico. In addition the diagnosis is also more prevalent among African Americans and those with less than a high school education or lower socioeconomic status.

There is usually co-morbidity with other psychological disorders, particularly mood disorders or anxiety disorders. Research also showed comorbidity between somatization disorder and personality disorders, especially antisocial, borderline, narcissistic, histrionic, avoidant, and dependent personality disorder.

About 10-20 percent of female first degree relatives also have somatization disorder and male relatives have increased rates of alcoholism and sociopathy.

As it has already been mentioned, the organic personality disorder is included in a wide group of personality and behavioural disorders. This mental health disorder can be caused by disease, brain damages or dysfunctions in specific brain areas in frontal lobe. The most common reason for this profound change in personality is the traumatic brain injury (TBI). Children, whose brain areas have injured or damaged, may present Attention Deficit Hyperactivity Disorder (ADHD), oppositional defiant disorder (ODD) and organic personality disorder. Moreover, this disorder is characterised as "frontal lobe syndrome". This characteristic name shows that the organic personality disorder can usually be caused by lesions in three brain areas of frontal lobe. Specifically, the symptoms of organic personality disorder can also be caused by traumatic brain injuries in orbitofrontal cortex, anterior cingulate cortex and dorsolateral prefrontal cortex. It is worth to be mentioned that organic personality disorder may also be caused by lesions in other circumscribed brain areas.

According to Professor Emily Simonoff of the Institute of Psychiatry, Psychology and Neuroscience, "childhood hyperactivity and conduct disorder showed equally strong prediction of antisocial personality disorder (ASPD) and criminality in early and mid-adult life. Lower IQ and reading problems were most prominent in their relationships with childhood and adolescent antisocial behaviour."

Organic personality disorder (OPD) is not included in the wide variety of group of personality disorders. For this reason, the symptoms and diagnostic criteria of the organic personality disorder are different from those of the mental health disorders, which are included in this various group of personality disorders. According to the Tenth Revision of the International Statistical Classification of Diseases and Related Health Problems ICD-10, it defines the organic personality disorder as the personality change, which can be caused by traumatic brain injury (TBI) that means there are specific brain areas of patients, which have been injured after a very strong accident. Moreover, according to the ICD-10, the organic personality disorder is associated with a "significant alteration of the habitual patterns of premorbid behaviour". Furthermore, organic personality disorder is associated with "personality change due to general medical condition". There are crucial influences on emotions, impulses and personal needs because of this disorder. Thus, all these definitions about the organic personality disorder support that this type of disorder is associated with changes in personality and behaviour.

The Diagnostic and Statistical Manual of Mental Disorders revision IV (DSM-IV) describes passive–aggressive personality disorder as a "pervasive pattern of negativistic attitudes and passive resistance to demands for adequate performance in social and occupational situations."

Passive-aggressive behavior is the obligatory symptom of the passive–aggressive personality disorder. Persons with passive–aggressive personality disorder are characterized by procrastination, covert obstructionism, inefficiency and stubbornness.

Money disorders are the maladaptive patterns of financial beliefs and behaviors that lead to clinically significant distress, impairment in social or occupational functioning, due to financial strain or an inability to appropriately enjoy one’s financial resources. With the exception of pathological gambling and compulsive buying, psychology and the mental health fields have largely neglected dysfunctional money disorders. The term is contentious among mental health professionals and as of 2017, money disorder is not a clinical diagnosis in either the DSM or ICD medical classifications of diseases and medical disorders.

Types of behaviors, or “scripts”, related to money disorders include money avoidance, money worship, money status and money vigilance. Some mental health practitioners say that those afflicted with money disorders or who have problematic money beliefs can seek financial therapy. With financial therapy, financial planners and relationship therapists work together to provide comprehensive treatment to clients experiencing financial distress.

Somatization disorder (also Briquet's syndrome) is a mental disorder characterized by recurring, multiple, and current, clinically significant complaints about somatic symptoms, although it is no longer considered a clinical diagnosis. It was recognized in the DSM-IV-TR classification system, but in the latest version DSM-5, it was combined with undifferentiated somatoform disorder to become "somatic symptom disorder", a diagnosis which no longer requires a specific number of somatic symptoms. ICD-10, the latest version of the International Statistical Classification of Diseases and Related Health Problems, still includes somatization syndrome.

Passive–aggressive disorder may stem from a specific childhood stimulus (e.g., alcohol/drug addicted parents, bullying, abuse) in an environment where it was not safe to express frustration or anger. Families in which the honest expression of feelings is forbidden tend to teach children to repress and deny their feelings and to use other channels to express their frustration. For example, if physical and psychological punishment were to be dealt to children who express anger, they would be inclined to be passive aggressive.

Children who sugarcoat hostility may have difficulties being assertive, never developing better coping strategies or skills for self-expression. They can become adults who, beneath a "seductive veneer," harbor "vindictive intent," in the words of US congressman/psychologist Timothy F. Murphy, and writer/practicing therapist Loriann Oberlin. Alternatively individuals may simply have difficulty being as directly aggressive or assertive as others. Martin Kantor suggests three areas that contribute to Passive–aggressive anger in individuals: conflicts about dependency, control, and competition, and that a person may be termed Passive–aggressive if they behave so to few people on most occasions.

Murphy and Oberlin also see passive aggression as part of a larger umbrella of hidden anger stemming from ten traits of the angry child or adult. These traits include making one's own misery, the inability to analyze problems, blaming others, turning bad feelings into angry ones, attacking people, lacking empathy, using anger to gain power, confusing anger with self-esteem, and indulging in negative self-talk. Lastly, the authors point out that those who hide their anger can be nice when they wish to be.

Traumatic events can lead to a disruption of the standard development of the central nervous system, which can generate a release of hormones that can change normal patterns of development.

Aggressiveness and impulsivity are among the possible symptoms of ASPD. Testosterone is a hormone that plays an important role in aggressiveness in the brain. For instance, criminals who have committed violent crimes tend to have higher levels of testosterone than the average person. The effect of testosterone is counteracted by cortisol which facilitates the cognitive control of impulsive tendencies.

One of the neurotransmitters that have been discussed in individuals with ASPD is serotonin, also known as 5HT. A meta-analysis of 20 studies found significantly lower 5-HIAA levels (indicating lower serotonin levels), especially in those who are younger than 30 years of age.

J.F.W. Deakin of University of Manchester's Neuroscience and Psychiatry Unit has discussed additional evidence of a connection between 5HT (serotonin) and ASPD. Deakin suggests that low cerebrospinal fluid concentrations of 5-HIAA, and hormone responses to 5HT, have displayed that the two main ascending 5HT pathways mediate adaptive responses to post and current conditions. He states that impairments in the posterior 5HT cells can lead to low mood functioning, as seen in patients with ASPD. It is important to note that the dysregulated serotonergic function may not be the sole feature that leads to ASPD, but it is an aspect of a multifaceted relationship between biological and psychosocial factors.

While it has been shown that lower levels of serotonin may be associated with ASPD, there has also been evidence that decreased serotonin function is highly correlated with impulsiveness and aggression across a number of different experimental paradigms. Impulsivity is not only linked with irregularities in 5HT metabolism, but may be the most essential psychopathological aspect linked with such dysfunction. Correspondingly, the DSM classifies "impulsivity or failure to plan ahead" and "irritability and aggressiveness" as two of seven sub-criteria in category A of the diagnostic criteria of ASPD.

Some studies have found a relationship between monoamine oxidase A and antisocial behavior, including conduct disorder and symptoms of adult ASPD, in maltreated children.

BFRBs are among the most poorly understood, misdiagnosed, and undertreated groups of disorders. BFRBs may affect at least 1 out of 20 people. Trichotillomania alone is believed to affect 10 million people in the United States.

Personality disorder not otherwise specified (also known as personality disorder NOS or PDNOS) is a DSM-IV Axis II personality disorder.

The DSM-5 does not have an equivalent to Personality Disorder NOS. However Personality disorder-trait specified (PD-TS) remains under consideration for future revisions. The DSM 5 "Unspecified Disorder" is not a personality disorder, it is used to enhance specificity of an existing disorder or it is an emergency diagnosis unto itself (i.e. Unspecified Mental Disorder, 300.9), without being attached to another disorder.

Pathological demand avoidance (PDA) is a proposed subtype of autism characterized by an avoidance of demand-framed requests by an individual. It was proposed in 1980 by the UK child psychologist Elizabeth Newson. The Elizabeth Newson Centre in Nottingham, England carries out assessments for the NHS, local authorities and private patients around autism spectrum disorder, which include, but are not exclusively PDA.

PDA behaviours are consistent with autism, but have differences from other autism subtypes diagnoses. It is not recognised by either the DSM-5 or the .

Dissociative disorder not otherwise specified (DDNOS) is a mental health diagnosis for pathological dissociation that matches the DSM-5 criteria for a dissociative disorder, but does not fit the full criteria for any of the specifically identified subtypes, which include dissociative identity disorder, dissociative amnesia, and depersonalization/derealization disorder. The International Statistical Classification of Diseases and Related Health Problems (ICD-10) refers to the diagnosis as "Other dissociative and conversion disorders".

Examples of DDNOS include chronic and recurrent syndromes of mixed dissociative symptoms, identity disturbance due to prolonged and intense coercive persuasion, disorders similar to dissociative identity disorder, acute dissociative reactions to stressful events, and dissociative trance.

DDNOS is the most common dissociative disorder and is diagnosed in 40% of dissociative disorder cases. It is often co-morbid with other mental illnesses such as complex posttraumatic stress disorder, major depressive disorder, generalized anxiety disorder, personality disorders, substance abuse disorders and eating disorders.

Attachment disorder is a broad term intended to describe disorders of mood, behavior, and social relationships arising from a failure to form normal attachments to primary care giving figures in early childhood. Such a failure would result from unusual early experiences of neglect, abuse, abrupt separation from caregivers between 6 months and three years of age, frequent change or excessive numbers of caregivers, or lack of caregiver responsiveness to child communicative efforts resulting in a lack of basic trust. A problematic history of social relationships occurring after about age three may be distressing to a child, but does not result in attachment disorder.

The term attachment disorder is used to describe emotional and behavioral problems of young children, and also applied to school-age children, teenagers and adults. The specific difficulties implied depend on the age of the individual being assessed, and a child's attachment-related behaviors may be very different with one familiar adult than with another, suggesting that the disorder is within the relationship and interactions of the two people rather than an aspect of one or the other personality. No list of symptoms can legitimately be presented but generally the term attachment disorder refers to the absence or distortion of age appropriate social behaviors with adults. For example, in a toddler, attachment-disordered behavior could include a failure to stay near familiar adults in a strange environment or to be comforted by contact with a familiar person, whereas in a six-year-old attachment-disordered behavior might involve excessive friendliness and inappropriate approaches to strangers.

There are currently two main areas of theory and practice relating to the definition and diagnosis of attachment disorder, and considerable discussion about a broader definition altogether. The first main area is based on scientific enquiry, is found in academic journals and books and pays close attention to attachment theory. It is described in ICD-10 as reactive attachment disorder, or "RAD" for the inhibited form, and disinhibited attachment disorder, or "DAD" for the disinhibited form. In DSM-IV-TR both comparable inhibited and disinhibited types are called reactive attachment disorder or "RAD".

The second area is controversial and considered pseudoscientific. It is found in clinical practice, on websites and in books and publications, but has little or no evidence base. It makes controversial claims relating to a basis in attachment theory. The use of these controversial diagnoses of attachment disorder is linked to the use of pseudoscientific attachment therapies to treat them.

Some authors have suggested that attachment, as an aspect of emotional development, is better assessed along a spectrum than considered to fall into two non-overlapping categories. This spectrum would have at one end the characteristics called secure attachment; midway along the range of disturbance would be insecure or other undesirable attachment styles; at the other extreme would be

non-attachment. Agreement has not yet been reached with respect to diagnostic criteria.

Finally, the term is also sometimes used to cover difficulties arising in relation to various attachment styles which may not be disorders in the clinical sense.

Masked depression (MD) was a proposed form of atypical depression in which somatic symptoms or behavioural disturbances dominate the clinical picture and disguise the underlying affective disorder. The concept is not currently supported by the mental health profession.

Disinhibited attachment disorder of childhood (DAD) according to the International Classification of Diseases (ICD-10), is defined as:

Disinhibited attachment disorder is a subtype of the ICD-10 category F94, "Disorders of social functioning with onset specific to childhood and adolescence". The other subtype of F94 is reactive attachment disorder of childhood (RAD – F94 .1).

Synonymous or similar disorders include Affectionless psychopathy and Institutional syndrome.

Within the ICD-10 category scheme, disinhibited attachment disorder specifically excludes Asperger syndrome (F84.5), hospitalism in children (F43.2), and hyperkinetic disorders (F90.-).

The majority of 1-year-old children can tolerate brief separations from familiar caregivers and are quickly comforted when the caregivers return. These children also use familiar people as a "secure base" and return to them periodically when exploring a new situation. Such children are said to have a secure attachment style, and characteristically continue to develop well both cognitively and emotionally.

Smaller numbers of children show less positive development at age 12 months. Their less desirable attachment styles may be predictors of poor later social development. Although these children's behavior at 12 months is not a serious problem, they appear to be on developmental trajectories that will end in poor social skills and relationships. Because attachment styles may serve as predictors of later development, it may be appropriate to think of certain attachment styles as part of the range of attachment disorders.

Insecure attachment styles in toddlers involve unusual reunions after separation from a familiar person. The children may snub the returning caregiver, or may go to the person but then resist being picked up. They may reunite with the caregiver, but then persistently cling to him/her, and fail to return to their previous play. These children are more likely to have later social problems with peers and teachers, but some of them spontaneously develop better ways of interacting with other people.

A small group of toddlers show a distressing way of reuniting after a separation. Called a disorganized/disoriented style, this reunion pattern can involve looking dazed or frightened, freezing in place, backing toward the caregiver or approaching with head sharply averted, or showing other behaviors that seem to imply fearfulness of the person who is being sought. Disorganized attachment has been considered a major risk factor for child psychopathology, as it appears to interfere with regulation or tolerance of negative emotions and may thus foster aggressive behavior. Disorganized patterns of attachment have the strongest links to concurrent and subsequent psychopathology, and considerable research has demonstrated both within-the-child and environmental correlates of disorganized attachment.

Environmental factors associated with the development of schizophrenia include the living environment, drug use, and prenatal stressors.

Maternal stress has been associated with an increased risk of schizophrenia, possibly in association with reelin. Maternal Stress has been observed to lead to hypermethylation and therefore under-expression of reelin, which in animal models leads to reduction in GABAergic neurons, a common finding in schizophrenia. Maternal nutritional deficiencies, such as those observed during a famine, as well as maternal obesity have also been identified as possible risk factors for schizophrenia. Both maternal stress and infection have been demonstrated to alter fetal neurodevelopment through pro-inflammatory proteins such as IL-8 and TNF.

Parenting style seems to have no major effect, although people with supportive parents do better than those with critical or hostile parents. Childhood trauma, death of a parent, and being bullied or abused increase the risk of psychosis. Living in an urban environment during childhood or as an adult has consistently been found to increase the risk of schizophrenia by a factor of two, even after taking into account drug use, ethnic group, and size of social group. Other factors that play an important role include social isolation and immigration related to social adversity, racial discrimination, family dysfunction, unemployment, and poor housing conditions.

It has been hypothesized that in some people, development of schizophrenia is related to intestinal tract dysfunction such as seen with non-celiac gluten sensitivity or abnormalities in the intestinal flora. A subgroup of persons with schizophrenia present an immune response to gluten different from that found in people with celiac, with elevated levels of certain serum biomarkers of gluten sensitivity such as anti-gliadin IgG or anti-gliadin IgA antibodies.