The components of the decline in mortality from ischaemic heart disease in Finland were studied by analysing the changes in incidence and prognosis between 1972 and 1981. Using personal identification numbers, hospital discharge records and death certificates were linked for all men and women aged 40-64. During this period mortality decreased 15.9% in men and 23.5% in women, incidence 14.2% in men and 19.3% in women, being greatest among 40-49 year olds living in urban areas, and case fatality 7.3% in men and 10.3% in women, owing primarily to a decrease in patients dying of ischaemic heart disease without being admitted to hospital; survival was also better among patients admitted to hospital. Factors explaining these changes remain unknown because data on risk factors and factors influencing prognosis are limited and largely ecological.
Cites: Circulation. 1984 Sep;70(3):345-96744538
Cites: Circulation. 1984 Sep;70(3):331-66744536
Cites: N Engl J Med. 1984 Nov 1;311(18):1144-76482932
Cigarette smoking and alcohol use habits in Finland and Sweden were studied using data from the Finnish and Swedish studies on like-sexed adult twin pairs aged 18-47 (total of 20 056 pairs). Finnish men were heavier consumers of tobacco and alcohol than Swedish men. When heavy consumers (greater than 500g of alcohol/month and greater than 20 cigarettes/day) were considered, the prevalence rate was 9.7% in Finnish men and 5.1% in Swedish men. This difference might account for the higher morbidity in Finland than in Sweden from many smoking- and alcohol-associated diseases. Genetic factors in smoking and alcohol use were assessed by comparing observed and expected coincidence rates, and by multivariate analyses. Genetic and familial effects were defined as an excess coincidence in monozygotic (MZ) pairs compared to dizygotic (DZ) pairs, and by an increased DZ coincidence rate compared to that expected. Significant genetic and familial effects were observed for cigarette smoking, and for smoking more than one pack of cigarettes a day. Significant familial effects for alcohol use was observed, and a significant genetic effect was obtained for men. A significant genetic effect could not be observed for the combined heavy use of alcohol and heavy smoking. The genetic and familial effects seemed to be mostly independent of country and sex.
Two large-scale studies of adult like-sexed twin pairs are ongoing in Sweden and Finland. Both studies comprise an unselected series that has been studied in a comparable fashion. Zygosity determination and health questionnaire data-gathering were carried out in 1973 for the Swedish study and in 1975 for the Finnish study for the comparable age groups. Data on hospital usage, cancer incidence and mortality are collected by record-linkage from the respective national registries. Cross-national twin studies can permit testing of hypotheses of the relationships between genetic and cultural factors and major chronic diseases and their risk factors.
Kinships composed of twin parents, their spouses and children, offer a robust and flexible sampling design for research in genetic epidemiology. Families-of-twins designs circumvent some of the sampling problems that arise when independent data sets are combined, and these designs provide unique evaluations of maternal influences, assortative mating and X-linkage. Unfortunately, empirical studies of families of twin parents have been limited by relatively small samples and by the self-selection biases intrinsic in ascertainment of families from volunteer twin registries. A large and representative cohort of monozygotic and dizygotic twin parents, drawn from a population-based twin registry, provides the optimal sampling frame for twin-family research. This paper reviews the sampling considerations underlying the initial family study based on the Finnish Twin Cohort and evaluates the representativeness of the sampled twins. Spouses and adult children (over 18 years) of 236 pairs of twins, about equally divided by gender and zygosity, were evaluated by a postal questionnaire. Individual response rates exceeded 86% and in 464 of the 472 nuclear families (98.3%), at last one member of the twin's family completed the questionnaire. The sampled twins, selected for fecundity to maximize statistical power of the obtained data, were broadly representative of non-selected twins drawn from the Cohort, with whom they were matched on age, gender, and zygosity. Such results suggest that the Finnish Cohort has excellent potential for extended twin-family research designs.
This study is based on data from 165 adult twin pairs separated at 10 years or less. Information on personality factors: extraversion (E) and neuroticism (N) (EPI scale short from), life satisfaction (LS) (Allardt) and stress of daily activities (SDA) was obtained as part of the questionnaire study carried out in the entire Finnish Twin Cohort in 1975. Later in 1979 a questionnaire sent to the twins reared apart yielded a scale (range 7-30 points) measuring the environmental dissimilarities after separation (reliability 0.83). The effect of separation on personality factors by analysis of variance of individual data was studied. Sex, zygosity and age-at-separation were included in the models. The overall explanatory rates were low (2.1-4.4%). The definitive study group was formed by selecting those pairs with a dissimilarity score greater than 15. The following intraclass correlations were obtained.
Within the Finnish Twin Cohort of like-sexed adult twin pairs, a subgroup of pairs separated at an early age has been identified. In 165 pairs, both cotwins responded to questionnaires in 1975 and 1979. An environmental dissimilarity score was formed which consists of items on whether the twins had lived after separation in the same community, attended the same school, were on the same grade at school, how often the cotwins met, how often they met common friends and relatives and whether they attended the same clubs etc, or not. To validate the zygosity diagnosis obtained by questionnaire in 1975, those pairs whose zygosity was unknown as well as those with the least contact after separation were contacted for blood sampling (11 bloodgroups). Of 15 pairs with no zygosity diagnosis, 10 responded (1 no address,2 abroad,2 refused). Six pairs were classified MZ and 4 DZ. In 12 MZ and 8 DZ pairs undergoing bloodgroup determination, the classification of only one pair changed from DZ to MZ. The following intraclass correlations for height and weight were found.
Data on alcohol use and smoking habits was available from the 1975 questionnaire of the entire cohort. Prior to pairwise analyses, the data of individuals was compared to that of age-sex matched groups of pairs reared together. The early separated twins had a higher alcohol consumption, while for smoking only slight differences were observed compared to twins reared together. Probandwise concordance rates were computed from smoking status (ever smoker/never smoker), alcohol use (user/nonuser) and "heavy" drinking (half-bottle of spirits on one occasion at least once a month). The following results were obtained in those pairs with the environmental dissimilarity score greater than 15: (table; see text)
To evaluate genetic influences on the use and abuse of alcohol, we compared questionnaire measures of the frequency, quantity, and density of social drinking, and the frequency of alcohol-induced passouts self-reported by 879 monozygotic (MZ) and 1940 dizygotic (DZ) pairs of twin brothers, aged 24-49 yr. The measures of frequency, quantity, and density (heavy drinking once or more a month) significantly intercorrelate, and the self-reported alcohol consumption by this sample is satisfactorily stable and consistent with nationwide sales figures. None of the drinking measures was associated with twin type (zygosity), and only density correlated with age. Similarity of drinking habits among twin brothers was evaluated as a function of their genetic resemblance and age, the frequency of their social contact with one another, and the interactions of these terms. The effects were estimated from hierarchical linear regressions of a double-entry data matrix from which each twin's drinking was predicted from that of his twin brother, and that pair's age, zygosity, cohabitation status, and frequency of social contact. Significant genetic variance was found for each of the drinking measures with heritability estimates ranging from 0.36 to 0.40. Co-twins in more frequent social contact with one another reported greater similarity in their use of alcohol, but heritable variance remained after the effects of age and social contact were removed from both mean levels and co-twin resemblance. Reported frequency of passouts yielded significant, but equivalent, correlations in both MZ and DZ twins and no evidence of genetic influence.
Some health related psychosocial correlates of the Eysenck neuroticism scale were examined in a questionnaire study of 1501 monozygotic (MZ) and 3455 dizygotic (DZ) male twin pairs representing the adult male twin population in Finland. In analyses of the individuals, 34% of the variance in neuroticism was associated to: psychological variables (stress of daily activities, life satisfaction, quality of sleep, and extroversion - the explanatory rate of this variable set was 30%), psychotropic drugs (5%), alcohol use (4%), and smoking (2%). Neuroticism was also associated to social, life change, and medical variables. In pairwise analyses, the heritability estimate (h2) was 0.54 for pairs living together and 0.39 for pairs living apart. It seems that heritability estimates are confounded by the closer intrapair relationship between members of MZ than DZ pairs. In pairwise analyses, 23% of the intrapair difference of neuroticism in MZ pairs was associated to intrapair differences in the aforementioned variables. The following explanatory rates were found: psychological variables, 21%; psychotropic drugs, 2%; alcohol use, 2%; and smoking, 1%. Neuroticism of pairs discordant for background variables showed similar intrapair differences as between individuals in the following variables: service vs farming work, use of alcohol, use of antacids, hypertension, heavy physical work, quality of sleep, changes of workplace for negative reasons, smoking, and use of tranquillizers. It appears that in Finland environmental factors explain at least 61% of the variability in neuroticism, and that factors determining neuroticism are also associated to health related behavior such as smoking, use of alcohol and psychotropic drugs.