Some factors associated with concordance and discordance with respect to schizophrenia in monozygotic twins

Environmental and Hereditary Factors in the Schizophrenias of Old Age (“Late Paraphrenia”) and their Bearing on the General Problem of Causation in Schizophrenia

The paraphrenias raise a number of problems common to many other disorders in the field of psychiatry, and their solution might therefore advance knowledge in a number of directions. The relationship between paraphrenic, paranoid and schizophrenic illness has long been disputed, and no view at present commands general acceptance. It has seemed to us that these controversies have often turned upon unacknowledged assumptions as to whether clinical, prognostic or genetic criteria, or all of these, were to be employed to decide the issue.

Genetics of Schizophrenia: Overview of Methods, Findings and Limitations

Genetics constitute a crucial risk factor to schizophrenia. In the last decade, molecular genetic research has produced novel findings, infusing optimism about discovering the biological roots of schizophrenia. However, the complexity of the object of inquiry makes it almost impossible for non-specialists in genetics (e.g., many clinicians and researchers) to get a proper understanding and appreciation of the genetic findings and their limitations. This study aims at facilitating such an understanding by providing a brief overview of some of the central methods and findings in schizophrenia genetics, from its historical origins to its current status, and also by addressing some limitations and challenges that confront this field of research. In short, the genetic architecture of schizophrenia has proven to be highly complex, heterogeneous and polygenic. The disease risk is constituted by numerous common genetic variants of only very small individual effect and by rare, highly penetrant genetic variants of larger effects. In spite of recent advances in molecular genetics, our knowledge of the etiopathogenesis of schizophrenia and the genotype-environment interactions remain limited.

Genetic risk of neuropsychological impairment in schizophrenia: a study of monozygotic twins discordant and concordant for the disorder

We used a paradigm involving monozygotic (MZ) twin pairs discordant for schizophrenia (n = 20) and concordant for schizophrenia (n = 8), as well as normal MZ twin pairs (n = 7) in order to study cognitive measures of genetic risk in schizophrenia. A comparison between the unaffected twins from the discordant sample and the normal twins indicated subtle attenuations in some aspects of memory and executive functioning in the unaffected group and thus provided evidence for cognitive markers of a genetic component in schizophrenia. A comparison of the affected twins from the discordant pairs and the concordant twins yielded virtually no differences, suggesting that a distinction between familial and sporadic cases is not valid in this sample. Large differences between unaffected and affected members of discordant pairs on a wide variety of variables, including IQ, attention, memory, and executive function, highlighted the magnitude of disease-specific factors.

Family history and birthweight in monozygotic twins concordant and discordant for psychosis

In a sample of monozygotic twins, intrapair differences in reported birthweight were larger in those pairs discordant for later psychosis, compared to pairs concordant for psychosis. A trend towards less family history of psychiatric disorder was also found in the discordant pairs.

Family history and schizophrenia: characteristics of groups with and without positive family histories

Social and demographic characteristics were examined retrospectively in a sample of 475 hospitalized schizophrenics to test the hypothesis that they can be meaningfully distinguished by the presence or absence of psychiatric disorders in their relatives. Cases with a positive family history of psychiatric disorders (FHP cases) were significantly more likely to have been born in the United Kingdom and to have had older mothers. Those who had relatives with psychiatric disorders other than schizophrenia were significantly more likely to have been diagnosed as schizo-affective. The findings are thought to reflect a constitutional trait in parents of FHP cases leading to delayed child bearing. They also support the 'environmental stress' theory of immigrant psychosis and the hypothesized genetic link between schizo-affective and affective disorders.

Paraphrenia: paranoid states of late life. II. American research

In Part I of this study, a review of the European literature on paraphrenia demonstrated that the disorder affects a significant number of older persons and is probably part of the schizophrenic spectrum. Part II presents the current research evidence and issues concerning paraphrenia, a disorder commonly misdiagnosed or overlooked in the United States. Recommendations are made for a rigorous investigation of this group of patients that American psychiatry has not studied adequately. Comparisons of paraphrenic and schizophrenic patients undoubtedly will provide new insights into both the process of schizophrenia and the process of aging.

Can schizophrenia with premorbid asociality be genetically distinguished from the other forms of schizophrenia?

Sufficient data exist to establish a genetic basis for some forms of schizophrenia. However, genetic factors may not account for all the variance, and subtle forms of central nervous system (CNS) damage may have etiological significance for some schizophrenic subtypes. One such subtype may be chronic schizophrenia with premorbid asociality (SPA). To test this hypothesis, the risk of schizophrenia among relatives of probands who did or did not meet the criteria for SPA was examined. The incidence of schizophrenia in the relatives of SPA probands was lower than that in the relatives of non-SPA probands. This difference approached but did not reach statistical significance. Because most studies have found a higher familial genetic loading in chronic forms of schizophrenia, the apparently lower incidence of disorder in relatives of chronic schizophrenics with premorbid asociality seems to be a heuristic lead worth pursuing.

Dermatoglyphics in schizophrenia: the relevance of positive family history

In the present study dermatoglyphic features were studied in schizophrenics with and without positive family history of schizophrenia. It was found that the difference between normals and schizophrenics was further exaggerated in those schizophrenics with a positive family history for schizophrenia. The implications of the findings and the need for further work are highlighted.

Scope and methodology of twin studies

The use of twins as a research tool is still proving its worth both by the number of scientists engaged in twin research and by the significance of their results. Old, familiar research designs are finding new applications, and new research designs are appearing. Of greatest current interest are the epidemiological studies made possible by the assembly and the aging of large numbers of twins in twin registries. As an outgrowth partly of the twin registries, partly of conceptual and mathematical progress, new methods have emerged for diagnosis of twin types and for analysis of twin data. One line of development started with the questionnaire method of zygosity diagnosis and has given rise most recently to zygosity diagnosis by principal component analysis. Another line started with probability calculations and has led to the use of generalized distance and noncentral chi-square. The appropriateness of these methods in different contexts needs to be critically considered. Also of importance are the psychologists' new methods of extracting genetic “factors”. The greatest weakness of twin studies, long recognized, is their dependence on the assumption that DZ pairs provide an adequate control on the environmental differences within MZ pairs. This may be valid with respect to environmental influences that are highly self-selected. It is debatable for self-selected influences that differ among families, and clearly untenable for most influences imposed by the social environment peculiar to twins.

Chronological parameters, twin studies, and mental diseases

Genetics deals with ordered and directed biological change in time; psychiatry with the development or the breakdown over the human life span of thought, feeling, and social adaptation. With the growing acknowl-edgement of the contribution of the genotype to mental and emotional uniqueness, it is appropriate to con-sider chronological parameters of mental disease in a genetic framework. These parameters include age of onset of illness (in turn affecting clinical characteristics), sequence of morbid signs and symptoms, length of illness, periodicity of illness, and temporal relation of clinical episodes to other biological events. Data are reviewed from twin and family studies, retrospective and ongoing, that relate such time phenomena to genetic factors in psychiatric disorder. Among the conditions to be considered are schizophrenia, manic-depressive psychosis, Huntington's chorea, karyotype abnormalities, presenile and senile disease, and the psychobiological ageing process itself.

Twenty-one psychiatric cases and their MZ cotwins. A thirty years' follow-up

In 1941, I published a psychiatric study of 69 same-sexed pairs of twins. The index cases were derived from 8596 consecutive admissions to three mental hospitals and one psychiatric unit of a general hospital in South Sweden, every patient being checked for twin birth in the official birth registers. There was no pair with more than one index case. Upon examination, 21 pairs were considered more or less certainly MZ, and 48 DZ. The degree of certainty of the zygosity diagnosis was expressed by a special formula (Essen-Möller, 1941b).

Of the 21 index cases, 7 (N. 1-7 of the monograph) were at that time judged schizophrenic. The later course revaled that one more index case (N. 12) was a schizophrenic and should have been included into this diagnostic group, which I shall have to concentrate upon in this brief presentation.

Out of the 8 cotwins of the schizophrenic index cases, 5 had presented symptoms of mental disorder up to the time of my investigation, which took place almost thirty years ago. This corresponds so far to a concordance rate of 62%. However, all of the cotwin disorders were relatively mild and transient in nature and consisted mainly of depressive or anxiety states. Even if some of the disordered cotwins had spent some time in a nursing home or in a psychiatric ward of a general hospital, none of them had been admitted to a mental hospital. And, although several of the clinical pictures contained some single trait suggestive of schizophrenia — such as ideas of reference (N. 2 and 7) or hallucinations (N. 5) — in no case a proper diagnosis of schizophrenia could be made. The cotwin who came closest to this diagnosis was a man aged 35 (N. 1), who gave much thought to telepathic phenomena and the like; yet, he was comparatively open-minded and accessible to discussion of his ideas, and he had never been incapacitated by them. Thus, at the time of the first investigation, the correct rate of concordance for schizophrenia in fact was zero. This finding was the more striking as the two other samples published up to that time, those of Luxenburger (1928) and Rosanoff (1934), showed rates of concordance at about 70%, although Luxenburger (1934) later corrected his figure to 33%, for diagnostic reasons. Personally, I was inclined to attribute my zero finding to chance, the number of pairs being small, and also to the relatively short time of observation.

Causal explanations in psychiatry: a critique of some current concepts

The rules known as Koch's postulates have served as invaluable guides to the discovery of the specific causes of various infectious diseases. It may safely be assumed that their influence has also been great on the methods of study in the field of non-infectious diseases. For example, with slight modification Koch's postulates may be applied to the study of diseases caused by poisons. But can they be modified and applied with profit in psychiatric research? This is an important problem, and it cannot be discussed without reference, explicit or implicit, to philosophical assumptions. In this paper some consequences of the philosophy of science of Sir Karl Popper will be tentatively explored.

Schizophrenia in twins: 16 years' consecutive admissions to a psychiatric clinic

Recent developments in the vexed questions of the relative importance to be attributed to genetic and environmental factors in the aetiology of schizophrenia, and the manner in which they interact to produce a phenotypic psychosis, are highlighted by David Rosenthal's series of critical papers (1959–1962) on twin and family studies and the book edited by him chronicling the lives of a set of monozygotic quadruplets all concordant for schizophrenia (1963). In his thorough and open-minded critique Rosenthal argues that previously reported concordance rates for monozygotic (MZ) twins have been misleadingly high. To this point we shall return in a moment. Rosenthal finally concludes that “the best information we now have with respect to the whole broad question of heredity and environment in schizophrenia, is to be found mainly in the five major studies of twins.” Unlike some who have pointed out weaknesses in the studies, he believes that “our task is to determine their source, extent and implications, not to dismiss them offhandedly because they contain errors” (1962a, p. 132).

Schizoidness in twins

Discordant schizophrenic monozygotic twin pairs were examined in order to clarify the view interpreting schizoid disorders as attenuated or incomplete expressions of schizophrenic heredity. The aggregate observations indicate that typical schizophrenia can be paired with all types and degrees of schizophrenic or schizoid illness, including clinical normality. These intra-pair combinations seem to occur more or less at random. The reviewed schizoid states showing evidence of schizophrenic psychopathology represent one of the developmental phases of schizophrenic process. Yet the psychopathologic connection with schizophrenia is not evident in all deviations and non-deviant personality patterns. Thus the seeming continuum of schizophnic psychosis — schizoid disorder — neurotic character — normal personality may consist of two discrete series: one with underlying schizophrenic psychopathology, and the other independent of the psychotic process. This division might reflect a threshold effect, dependent upon a switch mechanism.