Etiology of Mental Illness Research Paper

1. Early Causes

1.1 Genetic Influences

The advances made by genetics in the last 25 years of the twentieth century have been enormous, and are discussed elsewhere. It may appear that few of these advances have yet had much impact on the causation of mental illness, because there have been few dramatic advances comparable with that of the identification of the gene for Huntington’s chorea in 1987 (Gilliam et al. 1987). However, there has been a steady growth in knowledge, best summarized as incremental mapping, which has helped to place the genetic contribution to a wide range of mental illness, in context.

The standard methods of studying the genetic component of causation of illness are the same in psychiatry as in other branches of medicine. The relative genetic risk of having, or developing, a particular mental disorder is determined by three research approaches; family, twin and adoption studies. Family studies identify people with the disorder through questions ( probands); the rates of disorder are identified in other family members and relatives, and then compared with the rates in the general population. From these figures it is possible to compute the numbers of people likely to develop the condition at some time in the future (the expectancy rate or morbid risk). A higher rate in immediate relatives compared with others, and greater rates than the general population, indicate a genetic contribution to the disorder.

However, environmental factors may also contribute to risk in family studies, and twin studies are better at distinguishing the genetic component. Monozygotic and dizygotic twin probands are compared with their co-twins for concordance rates (i.e., the rate of cooccurrence of the disorder in the other twin). If the ratio of the concordance rates for monozygotic (MZ) twins (who are similar to clones as they have identical genes) and dizygotic (DZ) twins is significantly greater than one, the disorder has a genetic component. Because there is often a bias in reporting disorder, it is preferable to derive probands and their co-twins from twin registers wherever possible (Puri and Tyrer 1998).

Even with twin studies, the effect of environment cannot be completely separated since there is a tendency, fortunately exhibited less now than formerly, for monozygotic twins to be treated as though they were the same person and to identify psychologically with each other to a greater extent than dizygotic twins. Adoption studies overcome this effect, and when they are carried out with monozygotic twins, are seen to their best advantage. Other studies include adoptee approaches in which one or both of the biological parents has the disorder but the adoptive parents have not, so the rates of disorder in the adoptees can be compared with a control population, and adoptee family studies in which the adoptee is the proband and the rate of disorder determined in the biological and adoptive parents.

The results of these studies in general, show that there is a strong genetic contribution to bipolar mood disorder and schizophrenia with MZ DZ ratios of greater than 3 (Hauge et al. 1968, Gottesman and Shields 1976) but this falls far short of that shown by a disorder such as Huntington’s chorea. A more common finding is that illustrated by personality disorder, in which twin studies suggest that most personality traits are equally contributed to by genetic and environmental factors (Livesley et al. 1998) and several models have been postulated for the interaction between these (Kendler and Eaves 1986). Now that the human genome is close to being identified, the techniques of molecular genetics are being used increasingly to identify specific genes associated with psychiatric disorder, but to date, only one clear disorder has been identified, fragile X syndrome, which affects males mainly and which has clear locus on the X chromosome (Sutherland 1979). However, a range of other disorders has been shown to be associated with chromosomal abnormalities, and approximately 40 percent of the causes of severe mental handicap (Down’s syndrome, phenylketoneuria, tuberose sclerosis, Hurler’s syndrome, Lesch-Nyhan’s syndrome and Tay Sach’s disease) are known to be caused by identifiable chromosome abnormalities that are potentially preventable by genetic counselling (Weatherall 1991).

1.2 Environmental Factors Before and During Birth

The time immediately before, during and shortly after birth is a very vulnerable one for the fetus or new-born infant. It is at these times that anoxia can lead to brain damage. The most obvious manifestation of this is loss of brain cells leading to learning disability in adult life, and better obstetric care and supervision of babies with low birth weight reduces this risk (Illsley and Mitchell 1984). There have also been a number of studies suggesting that the development of other mental illness, particularly schizophrenia and related disorders, is linked to obstetric difficulties (Geddes and Lawrie 1995), but there is some doubt about the methodology of some of these studies. More careful matching of cases and controls in a larger sample, however, has failed to replicate these findings, apart from prolonged labor and emergency Caesarian section being more common in schizophrenic probands (Kendell et al. 2000).

There is also evidence that infectious diseases, particularly when contracted before birth, may be associated with mental disorder. Schizophrenia is more common in those born in the winter months (Hare et al. 1973) and the case has been made, not altogether satisfactorily, that this could be a consequence of maternal influenza in the winter months (Adams et al. 1993). Another infectious disease linked to mental illness is rubella, which is associated strongly with learning disability (due to microcephaly), if infection is contracted in the first trimester of pregnancy.

1.3 Early Years of Development

The hypothesis that mental illness is a consequence of problems in early development has been active for many years and is one of the fundamental components of psychoanalysis. This argues that psychological conflicts encountered in early development that remain unresolved are likely to surface later in life in distorted form that psychoanalysis can succeed in decoding. This is perhaps best encapsulated in the phrase ‘give us a child to the age of five and let who will have him thereafter.’ Another approach initiated by the work of John Bowlby is the possibility that the earliest stages of the infant’s relationship with its mother can also lead to problems that arise again in adult life. This has led to the growth of attachment theory (Bowlby 1988) and has also stimulated psychoanalytical approaches to treatment.

These difficulties are often not associated with overt psychological trauma, or, if they are, it is usually within the bounds of everyday experience. More severe trauma is associated with a different range of pathology. There are now many conditions which have been shown to be associated with severe psychological trauma in the early years of life, including borderline personality disorder, post-traumatic stress disorder, recurrent depressive episodes and a range of problems of sexual dysfunction. However, research into the subject has come in for some criticism, as data are almost entirely retrospective and subject to significant bias. This has been accentuated by the high profile of the multiple personality disorder, and its relationship with past childhood abuse, principally sexual abuse. Often, such abuse is unknown to the sufferer at first, but is evoked by assessment and treatment under hypnosis. There have been many claims that this form of assessment is suspect and creates what is commonly known as the ‘false memory syndrome’ (Brandon et al. 1998).

Depressive illness in adult life is also more likely to occur in those who have suffered the loss of a parent through separation, divorce or death (Harris et al. 1986). This is postulated to be due to increased vulnerability to adversity after adverse early experiences. The long gap between initial loss and the onset of depression has been studied by life events researchers, and the concept of ‘brought forward time’ introduced to compare it with the immediate response to a major life event.

2. Late Causes

2.1 Later Environmental Causes

There are a host of environmental causes of mental illness from late adolescence onwards that, unlike the previous ones described earlier, are determined to a much greater extent by the individual concerned. The group of conditions showing this characteristic most prominently, are the substance misuse disorders, as absence of indulgence can never lead to disorder. Although there are likely to be genetic factors that influence the extent that people become addicted to a substance (Kendler et al. 1995) by far the most important factor is repeated exposure and this is primarily an environmental issue. Alcohol is the most important of the substance misuse disorders, accounting for one third of all mental disorders and having harmful effects on around 10 percent of the population per year (Kessler et al. 1994), a staggering figure however it is interpreted.

Other important environmental causes are infections. These include viral, protozoal and bacterial organisms, and most recently, prion infections, such as the human form of bovine spongiform encephalopathy (BSE), and mental disorder is created when they affect the brain. The acquired immune deficiency syndrome (AIDS), neurosyphilis and viral encephalitis are the most important. Trauma to the brain is also an important cause of personality change and functional handicap, including dementia. Whenever the oxygen supply to the brain is significantly impaired, there is the danger of neuronal death and consequent organic mental illness, primarily dementia. Similar problems can be created by metabolic disturbances but these are more likely to be reversible. Thus a range of medical illnesses; hypertension, atherosclerosis, renal failure, hepatic failure, thyrotoxicosis, myxodema, sarcoidoisis, autoimmune diseases and Cushing’s disease (or any medical illness treated with steroids) may all be associated with mental disorder, of which anxiety, depression and dementia are the most common.

A more common environmental factor influencing the onset and nature of many common mental disorders is social deprivation. Epidemiological studies have consistently shown that almost all mental illness is more common in those of lower than higher social classes ((Hollingshead and Redlich 1958, Kessler et al. 1994). The reasons for this are much more difficult to unravel, but include specific aspects of deprivation ( poorer material circumstances—greater crime, traffic pollution, sub-standard housing, unemployment), less control over direction in life and a higher rate of adverse life events (Boulton 1998).

2.2 Recent Stress as a Precipitant of Mental Disorder

The notion that stress is the cause of much mental (and physical) disorder is a very old one. It has been researched heavily in recent years by those interested in the effect of life events on mental illness. Although some of the early causes of mental illness might be perceived as stressors that create mental illness, the general notion of stress as a recent precipitant is rather than a distant one. Early experiences may create a vulnerability to mental illness that is then activated by a stressful experience. These are often combined in the stress–diathesis model of mental illness, which places mental illness and stress on separate scales: low stress being associated with no mental illness; greater levels of stress creating illness in those who have a vulnerable diathesis, and very severe stress which may create symptoms of mental illness in almost anybody.

There are three specific mental illnesses which are defined as stress related: acute stress disorders, adjustment reactions and post-traumatic stress disorder. All of these present primarily with symptoms within the neurotic spectrum (e.g., anxiety, panic, depression, irritability, social withdrawal), and satisfy the common definition that they would not have occurred in the absence of a psychosocial stressor. Acute stress disorders can occur in almost anybody when under intolerable pressures (e.g., car accident) but resolve rapidly when the natural processes of restitution take place (usually within 24 hours). Adjustment disorders are longer-lasting, either because the stress is persistent (e.g., stress in a relationship), or because it is more intense. Post-traumatic stress disorder is associated with stress that is beyond the range of normal experience (e.g., earthquake, observing homicide) and which is associated with specific symptoms, including flash-backs of the traumatic event, nightmares, extreme avoidance of situations that evoke memories of the event, as well as the range of symptoms shown in adjustment disorders with generally greater intensity ( particularly depressive symptoms).

However, although these conditions are defined by the nature of the stressful experiences preceding them, there are many others in which stress is a provoking factor. These are specific codes for stressful events in both the DSM and ICD classifications (American Psychiatric Association 2000, World Health Organization 1992) and in a full diagnostic summary the nature of any associated stresses should be noted. In research work, stresses are often quantified into life events, whose intensity depends both on their nature and the extent of their (contextual) threat (Brown and Harris 1978) and there have been numerous studies that show that the onset of almost all mental illnesses is accompanied by a greater rate of life events than those without such illness. It is difficult to know to what extent, however, these could be regarded as causes of the illness in the true etiological sense, and it is more common to regard them as triggers or provoking factors. Thus, for example, it has been shown that exposure to high levels of critical expressed emotion in patients with schizophrenia is more likely to provoke relapse than if more normal expression of emotion is shown (Vaughn and Leff 1976) and interventions to reduce such emotion in families may have a beneficial effect (Pharoah et al. 2000). Even with this evidence, it is not suggested that critical expressed emotion is the cause of schizophrenia; it is the specific combination of a specific type of stress and its relationship to a particular illness that makes its effects shown. This ‘Achilles heel’ phenomenon, the activation of an illness by a particular combination of circumstances, is very common in mental illness, and gives support to the stress–diathesis model for many of the most common conditions encountered, particularly those in primary care.

The multifactorial nature of causation of mental illness is illustrated in the following case report, based on a real patient but with some important elements distorted to prevent identification.

Mrs A came as a refugee from a country in Sub-Saharan Africa where three members of her family were killed in front of her by rebels involved in fighting a civil war. She had become withdrawn and depressed after this, but was persuaded to flee the country by relatives and came to another country (the UK), where at the time she was being seen clinically, her application to stay in the country was being considered. Her relatives were also concerned that at times she had become more seriously disturbed and believed that her mind had been taken over by alien beings that had entered her body after a native witch doctor in her country had cursed her.

On assessment, she was shy but cooperative and keen to please. Her family history revealed that her mother had been unwell after one of her children was born and believed her body had been possessed by spirits that were preventing her from looking after her baby. A niece had also killed herself by walking into a swamp when unwell and allegedly possessed. During her childhood she did well at school but had times when she lost confidence in her own abilities and had always been more anxious than her brothers and sisters. In general, she had always had low self-esteem. Mental state examination revealed that she was persistently anxious with episodes of panic, particularly at night and when her husband was away from home (he worked variable hours). She also had vivid nightmares of her parents being killed in front of her by men wielding machetes, and was unable to have any sharp knives in her kitchen because they aroused such high levels of anxiety. She also had periods of quite deep depression when she felt that life was such a struggle that it would be easier to take her own life than continue to fight. Direct questioning about her alien experiences revealed she still believed that she had been cursed, as indeed had her whole family, and that twitching movements of her hands and arms indicated that she was still under external control. She was also very anxious that her application to remain in the country as a refugee might not be granted and kept asking the services to intervene on her behalf so she could stay.

A diagnosis of post-traumatic stress disorder, comorbid generalized anxiety disorder and recurrent depressive episode was made, and an unspecified diagnosis in the schizophrenia group, probably persistent delusional disorder, was also made.

In considering the causes of this complex problem, which is representative of many others who present to psychiatric services, the following etiological factors were considered:

(a) the family history of possession and being cursed, which could have a cultural explanation, but which might be better explained by a family history of schizophrenia, which Mrs A would be then more likely to have, because of its genetic component;

(b) the extreme stress occasioned by seeing members of her family killed in front of her (one of the characteristic features of post-traumatic stress disorder);

(c) her lifelong tendency of low self-esteem and tendency to be anxious; and

(d ) her current anxiety about the real possibility of being asked to leave the country if she did not achieve refugee status.

The etiology of these problems can be described in the form of a tree, in which the main trunk indicates her fundamental diatheses, her possible tendency to develop schizophrenia and the likelihood that she has some of the features of personality disturbance in the anxious fearful group (cluster C) (a mixture of genetic and constitutional factors). The branches include the relatively recent experiences of seeing her family killed, and the most recent, more characteristic of an adjustment disorder, indicate the stress of waiting to hear whether she would be allowed to stay in the country.

In constructing this tree, we need to be aware that there is a natural tendency for people to attempt to find causal explanations for everything in life, and sometimes these may be quite wrong. However, most of them have face validity, because in the search to make sense of a chaotic world, success in finding explanations make it more bearable and also easier to recall—a phenomenon nicely described as ‘effort after meaning’ by one of the earlier researchers on the subject (Bartlett 1932). Sometimes it is more accurate to say that the cause of a particular mental illness is unknown (idiopathic) but it makes us more authoritative to pick on a trunk, branch or leaf of the etiology tree and give a suitable explanation.

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