Genetics of neurotic depression

Molecular studies of major depressive disorder: the epigenetic perspective

Major depressive disorder (MDD) is a common and highly heterogeneous psychiatric disorder encompassing a spectrum of symptoms involving deficits to a range of cognitive, psychomotor and emotional processes. As is the norm for aetiological studies into the majority of psychiatric phenotypes, particular focus has fallen on the interplay between genetic and environmental factors. There are, however, several epidemiological, clinical and molecular peculiarities associated with MDD that are hard to explain using traditional gene- and environment-based approaches. Our goal in this study is to demonstrate the benefits of looking beyond conventional 'DNA+environment' and 'DNA x environment' aetiological paradigms. Epigenetic factors - inherited and acquired modifications of DNA and histones that regulate various genomic functions occurring without a change in nuclear DNA sequence - offer new insights about many of the non-Mendelian features of major depression, and provide a direct mechanistic route via which the environment can interact with the genome. The study of epigenetics, especially in complex diseases, is a relatively new field of research, and optimal laboratory techniques and analysis methods are still being developed. Incorporating epigenetic research into aetiological studies of MDD thus presents a number of methodological and interpretive challenges that need to be addressed. Despite these difficulties, the study of DNA methylation and histone modifications has the potential to transform our understanding about the molecular aetiology of complex diseases.

The epidemiology of mood disorders

This review provides an overview of the epidemiology, risk factors, and genetic epidemiology of mood disorders in adults and children. The magnitude and impact of mood disorders in the community outweighs that of most other chronic diseases. Although there is substantial knowledge regarding the sociodemographic risk factors for mood disorders, our understanding of the pathogenesis and classification still is evolving. Comorbidity of mood disorders with anxiety disorders and substance abuse has been documented widely. Whereas substance abuse and mood disorders seem to be independent etiologically, anxiety and mood disorders result from partially common etiologic factors. The results of family, twin, and adoption studies reveal that a positive family history is the most potent risk factor for mood disorders, particularly bipolar disorder. However, the specific factors that are transmitted in families still are unknown. The two areas that will inform future genetic research include phenomenologic studies that refine the validity of the current phenotypic classification of mood disorders, and application of study designs to elucidate specific factors that may explain the familial transmission of these disorders.

Nature, nurture and depression: a twin study

We studied a series of twins systematically ascertained through 214 probands (84 monozygotic, 130 dizygotic) who had had one or more episodes of hospital-treated major depression. A variety of definitions of depression were applied to the co-twins all of which resulted in (a) markedly higher rates of disorder than are found in the general population, (b) significantly higher monozygotic than dizygotic concordance. The results of applying a simple additive model in which depression is considered as a threshold trait suggested that both genetic factors and shared family environment make substantial and significant contributions to the familiality of depression.

The impact of the endogenous subtype on the familial aggregation of unipolar depression

The endogenous/non-endogenous distinction of unipolar major depression is widely accepted, as is the family study approach to the validation of diagnostic distinctions. Rates of affective disorders were examined in 689 first-degree relatives of 184 patients with unipolar major depression and were compared with 312 first-degree relatives of 80 healthy controls. Only unipolar depression and alcoholism were more common in families of depressed probands compared with families of healthy controls. As a variety of diagnostic definitions of endogenous depression have been proposed, probands and relatives were diagnosed in a polydiagnostic manner. None of the five diagnostic definitions of endogenous depression was able to identify patients with an increased familial risk of unipolar depression.

The genetics of neurotic-reactive depression: a reanalysis of Shapiro's (1970) twin study using diagnostic criteria

The present study explored the role of genetic factors in the development of neurotic depression. Case studies of 16 monozygotic (MZ) and 14 same-sex dizygotic (DZ) twins from Robert Shapiro's 1970 study of non-endogenous depression were rediagnosed by two raters blind to the zygosity and identity of each twin. Diagnoses were made using Research Diagnostic Criteria (RDC) and George Winokur's 1985 criteria for neurotic-reactive depression. When neurotic depression was operationally defined using Winokur's criteria plus RDC major or definite minor depression, the concordance rate for MZ twins was significantly greater than that for DZ twins. Our results contrast with Shapiro's negative findings, probably due to our use of formal diagnostic criteria and Shapiro's requirement that cotwins be hospitalized to be considered concordant. The present results suggest that genetic factors play a role in the etiology of at least some forms of neurotic depression.

The genetics of depression and manic-depressive disorder

Depressive disorders are more common in the relatives of depressed probands than in the population at large, and there is compelling evidence that the familial aggregation of bipolar disorder and severe unipolar depression is at least partly due to genetic factors. However, the evidence concerning 'non-endogenous' depression is less clear, and family environment probably plays a stronger role. Much current research is focused on two areas: firstly, the mode of inheritance of manic-depressive illness, with the use of molecular biological techniques to detect and localise major genes; and secondly, the ways in which familial predisposition and environmental insults combine to produce depressive disorder.

Twins' responses to pleasant, unpleasant, and life events

Pairs of monozygotic (n = 41) and same-sex dizygotic (n = 29) twins were administered the Pleasant Events Schedule, the Unpleasant Events Schedule (Lewinsohn & Amenson, 1978), and the Life Experiences Survey (Sarason, Johnson, & Siegel, 1978). These provided indices of both the frequency of and the emotional response to mood-related events. Monozygotic twins resembled one another more than dizygotic twins on all subscales of these measures, and the greater similarity was statistically significant for most of the subscales. This suggests that there may be a genetic influence on affect, which is expressed through both the frequency of engagement in and the emotional response to mood-related events. The results are discussed in the context of studies of genetic influences on subclinical levels of depression and other emotions.

The Camberwell Collaborative Depression Study. II. Investigation of family members

Out of a consecutive series of 130 potential probands with recent onsets of depression, 124 were deemed 'in scope' for a family interview study of social and genetic influences on depression. We were able to interview first-degree relatives of 83 probands (67% of those families 'in scope'). Unexpectedly, interviewed first-degree relatives had, on average, a significantly lower occupational status than the depressed probands. However, the rates of depression among the first-degree relatives were high. Based on a PSE-Catego classification, 17.2% of 244 relatives were current 'cases' of depression at the time of interview. This was significantly greater than the estimated population prevalence. Using a Past History Schedule in combination with the PSE, the lifetime prevalence of depressive illness, expressed as the proportion who had ever fulfilled PSE-Catego case criteria, was 38.9%. High rates of psychiatric treatment were also found in family members. The lifetime prevalence of any form of hospital treatment for depression in 315 first-degree relatives was 15.5%. This gives an age-corrected morbidity risk to age 65 years of 24.6%, as compared with a population estimate of 8.9%. In common with previous studies, significantly higher rates of depression were found among female than among male first-degree relatives for broader categories of disorder, but there was a small and nonsignificant excess of men among those relatives who had received in-patient treatment for depression. This apparent lessening of sex differences with more severe categories was not supported by an examination of 'lifetime ever' depressive symptoms, where severity was expressed as highest ever PSE-Catego-ID level.(ABSTRACT TRUNCATED AT 250 WORDS)

The Camberwell Collaborative Depression Study. III. Depression and adversity in the relatives of depressed probands

The relationship between life events and depressive disorder was assessed in 83 families ascertained through depressed probands. Contrary to expectation and to previous suggestions, we found no inverse relationship between the presence of familial loading and reactivity to stress. Thus the relatives of probands whose onset of depression followed life events or chronic difficulties had slightly higher lifetime rates of depression than the relatives of probands whose onset was not associated with adversity. There was only a weak and non-significant relationship between recent life events and current disorder among relatives, and no apparent tendency for life-event-associated depression to 'breed true' within families. Comparison with a community sample showed that the first-degree relatives of depressives had significantly elevated rates both of current depression and of recent threatening life events. This finding still held when proband-associated life events were discounted, suggesting that both liability to depression and propensity to experience life events are familial.

Psychiatric morbidity among relatives of different subgroups of neurotic depression

The morbidity risk for affective disorders was calculated among the relatives of subgroups of reactive-neurotic depressive patients. The patients were divided into reactive and neurotic depressives. The parents of the neurotic subgroup had a significantly lower morbidity risk of affective disorders in comparison with the parents of the reactive subgroup. The role of genetic and environmental factors in the etiology of reactive-neurotic depression was discussed.

Hazard, heredity and depression. A family study

The relationship between proband characteristics and familial aggregation of depression was assessed in an interview study of 83 families ascertained via probands who had a recent onset of depression. Contrary to expectations and to previous reports in the literature there were no differences between the frequencies of depression in the first degree relatives of probands who had or had not experienced adversity prior to the onset of their illness. Depression was actually slightly more common among the first degree relatives of probands who had experienced a threatening life event compared with the relatives of those who had not. Early onset of depression (before 32 yr) and a neurotic pattern of symptoms in probands were associated with significantly higher rates of current illness in relatives. However, both these differences disappeared when lifetime prevalence or morbid risk to age 65 were considered. Indeed the morbid risk of severe depression in the relatives of endogenously depressed probands was nearly twice that in the relatives of neurotic probands.

Family (genetic) studies in neurotic depression

Neurotic depression may be defined as a depression that occurs in the context of a long standing history of personality difficulties or neurotic symptoms. Two types of conditions fit this definition: (1) depressions secondary to personality disorder, neuroses or substance abuse; and (2) primary depressions with a family history of alcoholism. Depressions so defined show familial relationships with secondary depression, anxiety disorders, alcoholism, and depressions with personality disorders. The data suggest that these cluster in the same family and are related to the definition of neurotic depression given above. Whether these familial relationships are genetic awaits further research.

Similarity of monozygotic and dizygotic twins in level and lability of subclinically depressed mood

Ninety-two adult twin-pairs were recruited through advertisements in the local media. Twin zygosity was determined by use of the self-report inventory developed by Nichols and Bilbro (1966). The level and lability of subclinical depression were assessed. Mood level was assessed by the Beck Depression Inventory and by the MMPI D, D30, and DR Scales. Mood lability was assessed by daily administrations over a 2-week period of the Depression Adjective Check List (DACL) and the Wessman-Ricks Elation-Depression Mood Scales. Monozygotic twins resembled one another more than dizygotic twins in most measures of both level and lability of mood, which provides modest evidence for a genetic influence on subclinical levels of depression. Implications of these findings for the continuity hypothesis of depression are discussed.

The genetics of depression. A family study of unipolar and neurotic-reactive depressed patients

Sixty unipolar (23 male and 37 female) patients and 67 patients (25 male and 42 female) suffering from a neurotic-reactive depressive disorder, consecutively admitted to the Department of Psychiatry of Umeå University have participated in a family study aimed at identifying morbidity risks for psychiatric illnesses among first degree relatives (n = 437). Besides the classification of affective disorders used in Umeå for research purposes the patients have been classified, according to the ICD-9, DSM-III, age at onset (below or above 40 years), and the Winokur's classification of primary affective disorders. However, only the findings regarding the Umeå classification and the Winokur's classification are given in the present article. Of the patients 90% fulfilled Kendell's criteria for depression at the time of the investigation whereas the others were in a phase of remission when studied. The diagnosis of secondary cases were made without knowledge of the diagnoses of the probands. Among relatives of unipolar probands only two secondary cases of bipolar affective disorder were found--one among parents, and one among siblings (MR% 1.1 and 0.6 respectively). The overall morbidity risk for affective disorders (MR% 22.8 among parents and 15.5 among siblings) proved to be higher than in previous studies. In the families of neurotic-reactive patients the morbidity risk for bipolar affective disorders was also very low (MR% 1.0 among parents and 0.7 among siblings), whereas the overall MR% for affective disorders proved to be surprisingly high (12.1 among parents and 6.7 among siblings). No increased risk for schizophrenia or alcoholism was found among the relatives of either group. When the relatives were divided according to their sex no clear-cut difference in morbidity risk emerged when fathers and brothers were compared with mothers and sisters but alcoholisms occurred more frequently in male relatives. Preliminary findings in second degree relatives suggest that secondary cases of affective disorders might occur among second degree relatives of patients classified as suffering from "sporadic depression" according to Winokur's classification.

Some recent developments in psychiatric genetics

The methods and results of some recent family, twin and adoption studies of childhood behaviour disorders, crime, alcoholism, psychopathic personality and neurosis are briefly described. The data of Slater (1938) on the parents and children of manic-depressives are reanalysed. Bipolar affective illness were more frequent in the families of bipolar than unipolar probands. There was no support for sex-linked inheritance in either group or for further genetic subdivision of the unipolar group according to age of onset or alcoholic or psychopathic family history. It is suggested that for the time being we may have to be satisfied with three broad and aetiologically overlapping clinical types of depression: bipolar, unipolar and reactive.