Animal research suggests a programming effect of prenatal stress in the fetal period, resulting in disruptions in behavioural and neuromotor development. Physiological changes that mediate these effects include alterations in the hypothalamic-pituitary-adrenal axis and in testosterone levels. This human study focuses on changes related to these physiological systems after prenatal stress exposure.
We examined the potential effect of prenatal stress associated with the Chernobyl disaster in an ongoing genetic epidemiological study in Finland. One birth cohort of twins (n = 121 twin pairs) was exposed in utero to maternal stress, and their saliva cortisol and testosterone levels at age 14 were compared with twins (n = 157 twin pairs) born one year later.
Cortisol levels in both sexes and testosterone levels among females were significantly elevated after prenatal exposure to maternal stress from the second trimester onwards, compared to reference groups of non-exposed adolescents. Exposure explains 3% of variance (p
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.
A deterministic questionnaire method for zygosity determination is developed for use in epidemiological studies of adult twins. It is based on the answers of both members of a twin pair to two questions on similarity and confusion in childhood. The algorithm of the method is used to determine the zygosity status of a twin pair at two different levels of certainty. The validity of the method is tested by making blood marker determinations of 11 polymorphic marker systems fro a random sample of 104 twin pairs. The agreement between questionnaire and blood marker diagnosis was 100%, but the stricter level of certainty left 8.7% in the nonclassified group. The genetical representativeness of the sample is tested by the allele distribution of the markers as compared to the Finnish population data as well as by the distribution of the number of intra-pair differences in blood markers.
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)