A family history study evaluated first-degree relatives of 49 probands with degree relatives of probands with other somatoform disorders and affective disorder. The risk for a complicated medical history was 8.0% in the first-degree relatives of the somatization disorder probands, compared to 2.3% and 2.5% in the control groups (P < .01).
One study evaluated 43 pairs of same-sex twins, including 30 MZ pairs and 13 DZ pairs. MZ twin concordance was 77% for any tics, compared to 23% for DZ twins. For Tourette’s syndrome per se, the MZ twin concordance was 53%, compared to the DZ twin concordance of 8%. These differences are significant.
Pooled family study data from Europe show an age-corrected morbid risk for schizophrenia of 5.6% in parents, 10.1% in siblings, and 12.8% in children. It is thought that the lower rate in parents is related to a relative decrease in fertility among schizophrenic patients. Because general population figures for morbid risk for schizophrenia are around 1%, all classes of first-degree relatives have a clear increase in prevalence. The risk for offspring of two schizophrenic parents is difficult to estimate because of the small number of cases but probably runs between 35% and 45% (in the pooled data it is 46.3%). Among second-degree relatives (eg, uncles, aunts, nephews, nieces, grandchildren), half-siblings, and cousins, the risk ranges from 2% to 4%.
Mental retardation is defined by subnormal scores on standardized testing. Intelligence quotient (IQ) cutoffs of 90, 70, and 50 are commonly considered to be the boundaries for mild, moderate, and severe mental retardation.
One study evaluated 145 first-degree relatives of 46 children with obsessive-compulsive disorder (OCD). The investigators found that of the 90 parents evaluated in person, 15 (17%) received a diagnosis of OCD, compared to 1.5% of the parents of 34 children with conduct disorder who served as a control group. This 17% rate is also significantly higher than the prevalence rate of 2% in the general population. Fathers were three times as likely as mothers to receive a diagnosis of OCD. Of the 56 siblings evaluated personally, three (5%) met criteria for OCD. When data were corrected for age, the morbid risk was 35% in siblings. This result should be viewed with caution because of the magnitude of the age correction for siblings. The probands all had severe childhood-onset OCD and were referred to the investigators for treatment protocols. It is possible that childhood-onset OCD represents a more severe form of the illness. Nevertheless, this carefully conducted family study reveals an increased risk for OCD among the first-degree relatives of OCD probands.
Considerable comorbidity has been reported for alcoholism and other Axis I disorders in individuals who abuse drugs, and a relationship has been found between the type of comorbid disorder (eg, alcoholism or affective disorder) in probands and the rate of that same disorder in relatives. Relatives of opiate-dependent probands are at significantly increased risk for substance abuse, alcoholism, antisocial personality disorder, and major depression, compared to control subjects.
Early family studies of ADHD noted alcoholism and sociopathy in male relatives of children with ADHD and hysteria in female relatives. This same constellation was not manifest in the adoptive parents of adopted children with ADHD.
Genetic etiologies for some forms of Alzheimer’s disease have been found, and specific genes that influence vulnerability have been identified (Table 6-5). A review of epidemiologic studies, however, is remarkable in that it does not show high heritability of the disorder. This observation is partly attributable to multiple environmental and genetic etiologic factors. It is also related to the variable age at onset for the condition. Early-onset causes are more likely to be heritable and may be determined by single genes. Late-onset cases are more likely to be multifactorial. Important genetic factors in late-onset cases may be obscured by the fact that mortality from other causes decreases familial aggregation.
Family studies of affective disorders have continually demonstrated aggregation of illness in relatives (Table 6-2). In a study at the National Institute of Mental Health, 25% of relatives of bipolar probands were found to have bipolar disorder or unipolar illness (depression) themselves, compared to 20% of relatives of unipolar probands and 7% of relatives of control subjects. In the same study, 40% of the relatives of schizoaffective probands demonstrated affective illness at some point in their lives. These data demonstrate increased risk in relatives of patients; they also show that the various forms of affective illness appear to be related in a hierarchical way. Relatives of schizoaffective probands may have schizoaffective illness themselves but are more likely to have bipolar or unipolar illness. Relatives of bipolar probands have either bipolar or (more likely) unipolar illness.
Conclusion: Epidemiology, Etiology, & Public Health
Epidemiology places psychiatric disorders in a broad context, which is not always apparent with individual patients. This comprehensiveness is the basis of the biopsychosocial model. Goldberg suggests a version of this model that considers three kinds of factors: those that promote vulnerability (or indeed resilience), those that “release” symptoms at a particular time, and those that determine how long a particular disorder will last. Koopman adds that there is now a shift to studying complex systems that create patterns of disease. Such studies are conducted by the comprehensive monitoring of individuals as individuals and when they interact with others and their environment.
Methods in Psychiatric Genetics
A scientific revolution has occurred in the field of genetics, with the advent of molecular biological techniques. Using these techniques, researchers have located genes, in specific regions of chromosomes, for many neuropsychiatric diseases: Huntington’s disease (chromosome 4), Friedreich’s ataxia (chromosome 9), neurofibromatosis (chromosome 17), and familial Alzheimer’s disease (chromosomes 1, 14, 19, and 21). After strong evidence for inheritance of a disorder has been found through family, twin, and adoption studies, the tools of molecular biology can be used to locate the relevant gene(s) and designate the precise abnormality.
Mental Disorder, Physical Health, & Social Functioning
A survey of the point prevalence of schizophrenia within three regions of Scotland was undertaken in 1996, replicating a similar survey conducted in 1981. In comparison to the 1981 study, the patients studied in 1996 had both more positive and negative symptoms and more nonschizophrenic symptoms. Some of the symptoms encountered involved physical health.
Religion & Mental Health
Although limited investigation has suggested an association between religion (or spiritual) health and general health (including mental health), the nature and degree of this association is not clear. Several authors have found an increase in depression among larger and generally older Protestant denominations. The specific religious creeds involved; the internalization of these creeds by the members of the organization; the psychological, social, and behavioral characteristics demanded of these beliefs; and the adherence of the believers to these demands have yet to be elucidated.
Rural-Urban Differences & the Social Drift Hypothesis
Another important finding of most epidemiologic studies is that the prevalence of some mental disorders, particularly schizophrenia, has been found to be higher in urban and industrialized areas than in rural areas. A number of explanations for this finding have been suggested: social migration (the downward drift of persons and families experiencing schizophrenia to lower socioeconomic levels), inbreeding among the mentally ill, and the greater availability in urban areas of services for the chronically mentally ill. These differences may also reflect the comparative integration and stability of rural areas. Leighton and colleagues, in their study of rural Nova Scotia, found that depression (and other psychiatric disorders) were more common for all ages in “disintegrated” communities. Given the recent emphasis on the genetic basis of many psychiatric disorders, more research must be done on the degree of possible inheritance of these disorders in populations, and on the social drift hypothesis, before firm conclusions can be reached.
The Biopsychosocial Model & the Web of Causation
The late George Engel promulgated a theoretical model, based on general systems theory, of the etiology of mental disease. Research had demonstrated, and indeed continues to demonstrate, that unitary explanations are not adequate to explain disease etiology or thus indicate appropriate prevention and treatment strategies. Engel suggested an interrelatedness among biological, psychological, and social factors. Biological factors included anatomic and molecular factors and those factors related to gender, age, ethnicity, and genetics. Psychological factors related to the individual’s personality. According to Engel’s theory, social factors included family, society, culture, and environment; other authors would include religious and spiritual as well as economic factors in this group. Engel also believed that the physician’s contribution, through a psychosocial presence, to this “collaborative pathway to health” was often inseparable from that brought by the patient.