Unselected Twin Research Articles

Intrapair difference in personality traits, and emotional and social adjustment in monozygotic twins.

During the last decade, there has been a growing interest in the advantages that MZ twin pairs offer for studying the effect of environmental factors on the development of emotional disturbances. Much of this research has been aimed at investigating the relationship between childhood differences and later discordance with regard to schizophrenia in MZ twin pairs. A few studies have used similar methodology to investigate the development of neurotic reactions. There has been very little work dealing with the causes of discordance in the normal personality development of MZ twin pairs. The paper presents some of the results from a larger twin project which show the relationship between childhood differences and differences in adulthood. The study examined differences in oral, obsessive, and hysterical personality traits, as well as differences in phobic fears, general neurotic symptomatology, occupational and marriage adjustment in 50 relatively unselected MZ twin pairs. The results show that many of the same childhood differences which have been reported to be associated with the discordance found in regard to schizophrenia and neuroses, are also related to differences in personality structure, emotional and social adjustment in less disturbed MZ twin pairs. Other childhood differences, however, seem to be more specifically related either to neurotic or to normal personality development, pointing to the importance of studying the relationship between specific intrapair differences in childhood and differences in various areas of later personality development.

Death-discordant twins--a new method to evaluate genetic factors in chronic diseases.

One of the most important lines of research on unselected large scale twin registries are mortality followups. Death-specific concordance rates have been calculated using different measures of concordance. These estimates are of great importance but they only reflect an "all or-none" classification of the genetic effect. It is suggested that mortality studies could be extended to, and include studies on, death-discordant twins. Such studies combine the advantages from mortality follow-ups on total twin populations with the detailed clinical investigation on subsamples. By examining the surviving cotwins with respect to various traits and supposed risk factors, an opportunity has been provided to study the genetic determination on the development of disease. This approach has been used in a study of ischaemic heart disease (IHD) and its risk factors in a representative subsample from the Swedish Twin Registry.

Materno-fetal transfer of IgG in multiple pregnancy

The concentration of the immunoglobin IgG was measured by radial immunodiffusion in paired umbilical cord and maternal sera in 30 unselected twin pregnancies. Total serum proteins, albumin, alpha-feto protein, transferrin, immunoglobins IgM IgA and IgE levels were also determined. In the majority of cases IgG concentration related more closely to that of the other twin than to birth weight and in some cases the IgG was greater in the twin of lower weight. As in singletons, mean IgG levels were higher in cord than maternal sera. The 3 cases of feto-fetal transfusion syndrome were exceptional in the large difference between IgG concentrations in recipient and donor twins, the IgG level in the donor being only 13%-51% of that in the recipient. The discrepancy was much greater than that found between the fetal produced proteins, which suggests that there may be a disturbance in materno-fetal placental transfer in this condition.

Cancer in MZ and DZ twins.

Important works on the question of hereditary influence on the occurrence of cancer with application of twin series are those by v. Verschuer and Kober (cf. Spranger and v. Verschuer, 1964), Jarvik and Falek (1961) and Harvald and Hauge (1963). Their findings are by and large consistent with most earlier reports (Schull et al, 1959) and indicate that hereditary factors do not seem to influence the development of cancer as such, but possibly play a role in the localization of the tumor. In view of the fact that (except for Harvald and Hauge's investigation) the twin series studied have been comparatively small and yielded statistically unreliable numbers of cancer of specific site, it seems to be of value to extend the data by reporting findings from the Swedish Twin Registry, comprising about 11000 unselected twin pairs.The present paper reports mortality and morbidity in cancer of different site as well as concordance rates for MZ and DZ twins. In addition, the influence of smoking habits on cancer development has been analyzed, as this environmental factor is known to be associated with certain forms of cancer, particularly lung cancer (Smoking and Health, 1964).Cancer data have been obtained from two sources, the Swedish Cancer Registry and the Registry of Causes of Death.The Swedish Twin Registry in the present report comprises 10 945 twin pairs, and covers, in principle, all same-sexed twins born in Sweden in 1886-1925, and still living in the country as unbroken pairs at the time of compilation (1961). A detailed report of the compilation procedures and demographic data is given by Cederlöf (1966).

HEREDITY OF CANCER ELUCIDATED BY A STUDY OF UNSELECTED TWINS.

In an unselected sample of 6,893 Danish twin pairs, a total of 1,038 cases of cancer were found. In the group of identical twins (1,528), 143 cancer probands had unaffected partners, 8 had partners with cancer of the same site, and 13 had partners with cancer of other localizations. In the same-sexed fraternal twins (2,609), the corresponding numbers were 292, 9, and 39. Thus the concordance rates in the two groups do not differ significantly, indicating that gene differences can only to a limited extent explain the diversity in the population with regard to the occurrence of malignant growth.