Academic journal article Social Behavior and Personality: an international journal

A Review of Genetic Factors in Depressive Affects

Academic journal article Social Behavior and Personality: an international journal

A Review of Genetic Factors in Depressive Affects

Article excerpt

This paper contains a review of genetic factors in depressive affects. A large number of research findings have been reported for this purpose, the most important of these being the twin study. Monozygotic and dizygotic twins have been differentiated. It has been found that monozygotic twins have a higher concordance rate for affective illness than do dizygotic twins. Moreover, bipolar and unipolar illness were found in the relatives of unipolar patients only. Thus affective illness in the first degree of relatives of bipolar patients was more than 30%. Genetic transmission was also found in linkage relationship. Chromosomal studies have also been reported. Phenotypic variations have also been found responsible for affective illness. In conclusion, a better clinical, biochemical and therapeutic investigation has been suggested for better understanding of genetic factors in affective illness.

The tremendous development of biological sciences and the establishment of genetics as a separate discipline in the late 20th century have revolutionized the thought process of psychologists to believe that human personality characteristics and behavior, even metabolic changes and diseases, are also determined to a great extent - by the genetical code of the species. In recent years, a considerable number of studies have been conducted to investigate the influence of genetical factors in affective illness and its various subtypes of depressive and manic syndromes (Mendlewicz, Linkowski & Wilmotte 1980; Mendlewicz & Rainer 1977). This paper contains a review of genetic factors in depressive affects.

The first investigation into the relationship between genetic origins of depressive symptoms was conducted in a study on twins. Rosanoff, Handy, and Rosanoff-Plesset (1934) distinguished between monozygotic and dizygotic twins. Both types of twins share a similar environment but they are genetically different. Monozygotic twins originate from the same gene. Hence they behave genetically as identical individuals. Dizygotic twins originate from two different genes. Hence they share only half of their genes and behave as siblings. Investigators argued that the study of twins allows comparison of concordance rates for a trait. Thus monozygotic twins have a higher concordance rate for affective illness than do dizygotic twins.

Kallman (1954) found that twin study is most appropriate for the investigation of human traits through the observation of the developmental process. Da Fonseca (1959) reported similar findings and concluded that both physical and mental development in twins provide empirical findings for explaining a large number of symptoms of affective disorder. Harvald and Hauge (1965) supported these findings in their twin study and concluded that the comparison of developmental rates for a trait can be carried out empirically in a twin study which provides a real situation for understanding the affective symptoms of such psychological diseases as depression, manic-depressive reaction, schizophrenia and other bipolar illnesses.

The findings from the twin study conducted by Price (1968) showed that the concordance rates in monozygotic twins vary between 50% and 92.5% as compared to 0-38.5% in dizygotic twins. The mean of concordance rates in monozygotic twins was 69.3% and that of dizygotic twins was 20%. These results strongly support the presence of genetic factors in the etiology of bipolar illness.

Furthermore, Price (1968) observed that identical twins reared apart from early childhood were characterized by bipolar illness and were diagnosed as affectively ill. It was also found that 8 out of 12 pairs were concordant for the diseases. These findings suggest that the predisposition to bipolar illness usually expresses itself regardless of the early environment.

These findings on twin and adoption studies on bipolar illness have shown that this illness tends to be familial. Kallman (1954), for example, showed that the lifetime risk for bipolar illness is significantly higher in twins (23. …

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