The contribution of hereditary factors in basal cell carcinoma of the skin has not been well defined at the population level. We aimed to assess the hereditary component in basal cell carcinoma by comparing its occurrence in monozygotic and dizygotic twin pairs. The Finnish Twin Cohort, comprising 12,941 adult, like-sex twin pairs with established zygosity and resident in Finland in 1975, was linked with the Finnish Cancer Registry. We identified 335 twin pairs in which at least one twin had basal cell carcinoma diagnosed between 1953 and 1996. Standardized incidence ratios, concordances, tetrachoric correlations and pairwise relative risks were computed by standard methods. Components of variance in liability were estimated by structural equation modelling. There was an elevated risk of basal cell carcinoma for the co-twin of a diseased twin, but no difference in risk by zygosity. During the prospective follow-up in 1976-96, the probandwise concordance was 7.7% in monozygotic and 7.0% in dizygotic pairs. Model fitting indicated that genetic factors were not needed to account for the distribution of basal cell carcinoma in twin pairs. These results confirm the major role of environmental factors in the aetiology of basal cell carcinoma.
Sleeptalking is usually benign but chronic cases in adults may relate to psychopathology. We hypothesize substantial genetic influences in the liability to sleeptalking and an association between sleeptalking and psychiatric disorders. In 1990 a questionnaire sent to the Finnish Twin Cohort yielded responses from 1298 monozygotic and 2419 dizygotic twin pairs aged 33-60 years. We used structural equation modelling to estimate genetic and environmental components of variance in the liability to sleeptalking. Register data on hospitalization and long-term antipsychotic medication were used to assess psychiatric comorbidity. The occurrence of childhood and adult sleeptalking was highly correlated. A gender difference was only seen in adults, with sleeptalking being more common in males than in females. The proportion of total phenotypic variance in liability to sleeptalking attributed to genetic influences in childhood sleeptalking was 54% (95% CI, 44-62%) in males and 51% (43-58%) in females, and for adults it was 37% (27-46%) among males and 48% (40-56%) among females. An association with psychiatric comorbidity was found only in adult sleeptalking, and it was highest in those with adult-onset sleeptalking (odds ratio, 3.77; 95% CI, 2.32-6.17). Sleeptalking is quite a persistent trait, also being common in adults. There are substantial genetic effects on sleeptalking both in childhood and as adults, which appear to be highly correlated. In adults psychiatric comorbidity is about twice as common in those with frequent sleeptalking, compared to those with infrequent or no sleeptalking, but most cases of sleeptalking are not associated with serious psychopathology.
Like other atopic diseases, hay fever is known to cluster in families. This clustering is due either to effects of a shared family environment or to genetic inheritance. By comparing the occurrence of hay fever among monozygous (MZ) and dizygous (DZ) twin pairs, we were able to estimate the contribution of genetic and environmental factors in the development of hay fever.
A questionnaire mailed to a nationwide sample of 2483 families with 16-year-old twins furnished data for the cumulative incidence of physician-diagnosed hay fever among these adolescents and their parents.
Among the 1765 twin pairs with data available for analysis, hay fever was reported for 14.1% of boys (95% CI=12.4-15.8%) and 10.0% of girls (95% CI=8.6-11.4%). The MZ twin pairs (probandwise concordance rate=60.3%, 95% CI =52-68%) were significantly more concordant for hay fever than were DZ twin pairs (31.5%, 95% CI=26-36%). Genetic factors accounted for 74-82% of the interindividual variability in liability to hay fever, variation in shared family environment for 7% at most, and unique (individual) environment for 18%.
Familial occurrence of hay fever is mainly due to genes predisposing to the trait. Environmental exposures shared in common by family members but varying between families appear to account for at most a modest proportion of the variability in risk of developing hay fever.
In 1975 and again in 1981, all adult twins in the population-based Finnish Twin Cohort were administered postal questionnaires yielding data on self-reported frequency and quantity of alcohol use. The longitudinal results provide information on the age-to-age stability of social drinking patterns among 13,404 (twin) individuals aged 18 to 43 at baseline; model-fitting the cross-temporal consistency of the twins' reported alcohol use yields unique estimates of the contribution of genetic and environmental factors to their individual age-to-age stabilities. Mean consumption levels did not change between 1975 and 1981. Patterns of social drinking were more stable in older (aged 24-43 at baseline) than younger (aged 18-23 at baseline) adult twins, and were more stable among men than women. Heritabilities were significant at both baseline and follow-up for all three alcohol measures in both genders and both age groups, with a median magnitude of 0.48. Both longitudinal genetic and environmental covariances were significant, and both were generally higher among older pairs. Genetic covariances (median magnitude = 0.68) were significantly higher than environmental covariances (median = 0.36). Analyses of absolute changes in alcohol use revealed heritable influences on the disposition to change. We conclude that genes contribute to both consistency and change in patterns of alcohol use from early to midadulthood.
We investigated whether BMI predicts type 2 diabetes in twins and to what extent that is explained by common genetic factors.
This was a population-based twin cohort study. Monozygotic (n = 4,076) and dizygotic (n = 9,109) non-diabetic twin pairs born before 1958 answered a questionnaire in 1975, from which BMI was obtained. Information on incident cases of diabetes was obtained by linkage to nationwide registers until 2005.
Altogether, 1,332 twins (6.3% of men, 5.1% of women) developed type 2 diabetes. The HR for type 2 diabetes increased monotonically with a mean of 1.22 (95% CI 1.20-1.24) per BMI unit and of 1.97 (95% CI 1.87-2.08) per SD of BMI. The HRs for lean, overweight, obese and morbidly obese participants were 0.59, 2.96, 6.80 and 13.64 as compared with normal weight participants. Model heritability estimates for bivariate variance due to an additive genetic component and non-shared environmental component were 75% (men) and 71% (women) for BMI, and 73% and 64%, respectively for type 2 diabetes. The correlations between genetic variance components (r (g)) indicated that one fifth of the covariance of BMI and type 2 diabetes was due to shared genetic influences. Although the mean monozygotic concordance for type 2 diabetes was approximately twice the dizygotic one, age of onset of diabetes within twin pair members varied greatly, irrespective of zygosity.
A 28-year follow-up of adult Finnish twins showed that despite high trait heritability estimates, only a fraction of covariation in BMI and incident type 2 diabetes was of genetic origin.
We studied the cumulative incidence, concordance rate and heritability for diabetes mellitus in a nationwide cohort of 13,888 Finnish twin pairs of the same sex. The twins were born before 1958 and both co-twins were alive in 1967. Data on diabetes were derived through computerized record linkage from death certificates, the National Hospital Discharge Register and the National Drug Register. Records were reviewed in order to assign a diagnostic category to the 738 diabetic patients identified. Of these patients 109 had Type 1 (insulin-dependent) diabetes, 505 Type 2 (non-insulin-dependent) diabetes, 46 gestational diabetes, 24 secondary diabetes, 38 impaired glucose tolerance and 16 remained unclassified. The cumulative incidence of diabetes was 1.4% in men and 1.3% in women aged 28-59 years and 9.3% and 7.0% in men and women aged 60 years and over, respectively. The cumulative incidence did not differ between monozygotic and dizygotic twins. The concordance rate for Type 1 diabetes was higher among monozygotic (23% probandwise and 13% pairwise) than dizygotic twins (5% probandwise and 3% pairwise). The probandwise and pairwise concordance rates for Type 2 diabetes were 34% and 20% among monozygotic twins and 16% and 9% in dizygotic twins, respectively. Heritability for Type 1 diabetes was greater than that for Type 2 where both genetic and environmental effects seemed to play a significant role.
Environmental factors are needed to explain the observed increase in the prevalence of asthma during recent decades, despite the existence of a recognised genetic component in asthma. A co-twin case-control study was undertaken to examine possible social risk factors for asthma.
Asthma diagnoses were based on register data of reimbursed asthma medication. During 17 years follow up of the Finnish twin cohort, 262 twin pairs discordant for incident asthma were identified. Conditional logistic regression for 1-1 matched data was used for risk calculation.
The atopic twin had an increased risk of asthma compared with the non-atopic co-twin (RR 2.91, 95% CI 1.81 to 4.68). The more educated twin had a decreased risk of asthma compared with his/her twin sibling with less education (RR 0.45, 95% CI 0.23 to 0.86), and the twin who participated in conditioning exercise had a decreased risk of asthma compared with the more sedentary co-twin (RR 0.55, 95% CI 0.34 to 0.88).
In addition to allergic diseases, educational level and physical activity are associated with adult onset asthma, which indicates a role for factors associated with life style.
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This study examined the change in heritability of adult body height across birth cohorts in Finland.
In 1981, cross-sectional questionnaires were completed by 10,968 twin pairs born before 1958. The effect of genetic factors was estimated via genetic modeling.
Heritability increased from the cohort born before 1929 (0.76, 95% confidence interval [CI] = 0.65, 0.88 in men; 0.66, 95% CI = 0.55, 0.77 in women) to that born in 1947 through 1957 (0.81, 95% CI = 0.73, 0.87 in men; 0.82, 95% CI = 0.75, 0.89 in women).
Heritability of height increased across Finnish birth cohorts born in the first half of this century and leveled off after World War II. Environmental factors, compared with genetic factors, appear to be more important among women than men.
Leptin is involved in the regulation of body weight, but the relative role of genetic and environmental influences on inter-individual variation in leptin levels is unknown.
To investigate the genetic and environmental contributions to the association of body mass index (BMI) with serum leptin levels, 58 monozygotic (MZ, 27M, 31F), and 74 like-sexed dizygotic (DZ, 32M, 42F) Finnish twin pairs aged 50--76 y were studied.
Serum leptin levels, weight, height, hip and waist measurements.
Women had higher mean leptin levels (16.8+/-9.5 ng/ml), and more overall variability in leptin levels than men (6.4+/-3.5 ng/ml; P
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.
This study identifies, in genetically informative data, familial and socioregional environmental influences on abstinence from alcohol at age 16.
Data are from FinnTwin 16, a population-based study of five consecutive birth cohorts of Finnish twins (N = 5,747 twin individuals), yielding 2,711 pairs of known zygosity. Measures of alcohol use, embedded into a health-habits questionnaire, were taken from earlier epidemiological research with nontwin Finnish adolescents. The questionnaire was administered sequentially to all twins as they reached age 16. Separate questionnaires, including measures of alcohol use and screening questions for alcohol problems, were received from 5,243 of the twins' parents.
Abstinence from alcohol to age 16 exhibits very significant familial aggregation, largely due to nongenetic influences. Abstinence rates are influenced by socioregional variation, sibling interaction effects and parental drinking patterns. Sibling and parental influences are greater in some regional environments than in others: the relative likelihood that a twin abstains, given that the co-twin does, or that both parents do, is shown to be modulated by socioregional variation.
Environmental contexts affect the likelihood of maintaining abstinence from alcohol to midadolescence, and socioregional variation modulates influences of siblings and parents. The results illustrate how genetically informative data can inform prevention research by identifying target variables for intervention efforts.
The problems of differentiation between environmental and genetic influences on the development of multiple sclerosis are well known. Twin studies may provide valuable information on this question. However, most published twin series are selected and no through clinical twin studies based on epidemiologic series have been carried out. In this study, all available same-sex twin pairs with clinically definite multiple sclerosis derived from the Finnish Twin Cohort of 15815 pairs were studied by clinical evaluation, magnetic resonance imaging, and visual and auditory evoked responses. The mean length of follow-up of the pairs after the onset of symptoms of multiple sclerosis was 20 years. Two of the seven monozygotic pairs were concordant; one was definitely so, and in the other, the co-twin of the index case had, in addition to clinical findings, white matter changes suggestive of multiple sclerosis in magnetic resonance imaging and abnormal visual evoked responses. All six dizygotic pairs were discordant. The frequency of the HLA antigen DR2 in probands (69%) was significantly increased, but the distribution among the healthy subjects and patients showed nonsignificant differences. The results indicate a genetic influence on the susceptibility to multiple sclerosis, although still unknown genetic determinants are possible involved.
To investigate the risk of cancer in children living close to overhead power lines with magnetic fields of > or = 0.01 microteslas (microT).
The whole of Finland.
68,300 boys and 66,500 girls aged 0-19 years living during 1970-89 within 500 m of overhead power lines of 110-400 kV in magnetic fields calculated to be > or = 0.01 microT. Subjects were identified by record linkages of nationwide registers.
Numbers of observed cases in follow up for cancer and standardised incidence ratios for all cancers and particularly for nervous system tumours, leukaemia, and lymphoma.
In the whole cohort 140 cases of cancer were observed (145 expected; standardised incidence ratio 0.97, 95% confidence interval 0.81 to 1.1). No statistically significant increases in all cancers and in leukaemia and lymphoma were found in children at any exposure level. A statistically significant excess of nervous system tumours was found in boys (but not in girls) who were exposed to magnetic fields of > or = 0.20 microT or cumulative exposure of > or = 0.40 microT years.
Residentia magnetic fields of transmission power lines do not constitute a major public health problem regarding childhood cancer. The small numbers do not allow further conclusions about the risk of cancer in stronger magnetic fields.
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Based on data in the Finnish Twin Registry, which was obtained by postal questionnaire, the prevalence of chronic bronchitis among non-smoking farmers was 3.6% and among a corresponding group of non-farmers (reference subjects) 3.4%. The six-year incidences of chronic bronchitis for these 2 groups were 2.7% and 0.7%, respectively. The difference in incidence between these groups was significant (p less than 0.001). The fact that the incidence among farming subjects was three times the incidence among non-farming subjects indicates that chronic bronchitis is a work-related disease among farmers. This is analogous to previous findings that symptoms compatible with chronic bronchitis occur more often among grain elevator workers than among urban dwellers. The occurrence of chronic bronchitis among both farmers and grain elevator workers probably is associated with exposure to grain dusts.
Eighteen pairs of monozygotic twins discordant for long-term occupational exposure to organic solvents were examined for disturbances of cardiovascular reflexes. All of the subjects were asymptomatic, and considered themselves healthy. No significant differences were observed between the exposed and the nonexposed twins. The finding suggests that occupational solvent exposure at these particular levels is unlikely to cause disturbances of the autonomic nervous function.
Farm environment in childhood may protect against sensitization, allergic rhinitis, and asthma.
Subjects were obtained from 10 667 Finnish first-year university students who responded to a questionnaire survey on IgE-mediated diseases. Two random samples were selected from 1631 respondents in Turku: subjects with asthma or wheezing, and subjects without asthmatic symptoms. A total of 296 subjects (72%) participated. Skin prick tests (SPT), measurements of IgE-antibodies, methacholine challenge, and bronchodilation tests were performed. Weighted occurrence of current asthma and sensitization among students from "childhood farm" and "childhood nonfarm" environments were analyzed.
Current asthma was found in 3.1% of subjects with childhood farm environment, and in 12.4% with nonfarm environment (odds ratio (OR) 0.22; 95% confidence interval (CI) 0.07-0.70). There were fewer positive SPT to birch (8.3 vs. 24.2%, OR 0.28, 95% CI 0.07-1.15) and timothy pollen (12.6 vs. 30.3%, OR 0.33, 95% CI 0.09-1.20) among subjects with childhood farm environment, but more sensitization to house-dust mite (22.0 vs. 4.9%, OR 5.43, 95% CI 1.60-18.46). Sensitization to cat (RAST class >/= 3) was less common in subjects with farm compared to nonfarm environments in childhood (1.5 vs. 13.1%; OR 0.10, 95% CI 0.02-0.47).
Farm environment in childhood protects against adult asthma and sensitization-especially to cat-the most important asthma related allergen. In contrast, sensitization to house-dust mite was more common in farming subjects.
To study twin resemblance for weight change (delta wt) and to assess the consistency of body mass index (BMI) over 6 years.
6 year follow-up based on identical mailed questionnaires in 1975 (baseline) and in 1981 (follow-up).
5967 same-sexed non-pregnant Finnish twin pairs aged 18-54 in 1975 (1106 male and 862 female monozygotic (MZ) and 2430 male and 1569 female dizygotic (DZ) pairs).
Intra-pair correlations of delta wt and BMI, estimates of genetic and environmental components of variance of delta wt and BMI.
Unadjusted mean delta wt was +2.0 (s.d. = 4.6) kg among MZ and 2.1 (4.9) kg among DZ male individuals. Corresponding values among MZ and DZ female individuals were +1.5 (4.4) kg and +1.7 (4.4) kg, respectively. Age and initial BMI together explained 8.0% of the male and 2.3% of the female phenotypic variance of delta wt. The intraclass correlations for delta wt (adjusted for age and initial BMI) for all pairs were 0.29 and 0.07 for MZ and DZ men and 0.25 and 0.05 for MZ and DZ women, respectively. The BMI of the twins increased slightly during the follow-up compared to the baseline values (23.9 (2.7) for MZ and 24.1 for DZ men and 23.0 (3.3) for MZ and 23.2 (3.42) for DZ women). The intra-class correlations for BMI at baseline (0.69 for MZ and 0.34 for DZ men and 0.67 for MZ and 0.29 for DZ women) were almost identical with the correlations at follow-up (0.67 for MZ and 0.32 for DZ men and 0.69 for MZ and 0.29 for DZ women). The intra-class correlations for both BMI and delta wt were consistently higher among pairs living together than among pairs living apart at baseline and at follow-up in both zygosity groups (MZ and DZ). Among pairs living apart at baseline, the longitudinal model for BMI showed that the correlation between genetic effects at baseline and at follow-up was very high (> 0.9 in all age groups among both genders). The correlations for environmental effects ranged from 0.50 to 0.67 during the follow-up period.
Weight changes in adults over a 6-year period appear to be determined by environmental effects rather than genetic factors. However, the genetic component in BMI is considerable and stable over time. Shared environment is likely to contribute to the resemblance of both delta wt and BMI among adult twin pairs, especially among MZ pairs.
Both hereditary and environmental factors are implicated in the aetiology of cutaneous neoplasms. Studies of twins make it possible to estimate the contribution of inherited genes to the development of disease.
To assess the importance of hereditary and environmental factors (including physical environment and lifestyles) in malignant melanoma and malignant nonmelanoma of the skin.
The Finnish Twin Cohort, comprising 25 882 adult like-sexed twins with established zygosity, was linked with the Finnish Cancer Registry to identify malignant skin cancers in a prospective follow-up from 1976 to 1997. Standardized incidence ratios were computed based on national rates.
Sixty twins were diagnosed with melanoma and 49 twins with nonmelanoma during the follow-up. The risks of these cancers did not differ from the risk in the population at large. There was only one pair where both twins had a malignant skin cancer (dizygotic male twins both with squamous cell carcinoma).
The near-total lack of concordance for skin cancer in twin pairs suggests that environmental and not hereditary effects are most important in the causation of malignant skin cancers in a white population with low levels of sun exposure.
Finland has a higher mortality overall and for major causes of death than Sweden, primarily in men. The objective of this study was to analyse mortality in migrants from Finland to Sweden.
A longitudinal study based on the Finnish Twin Cohort Study. Information about migration from Finland to Sweden, duration of stay in Sweden for the migrants, and deaths 1976-1995 was obtained from national registers. Observed numbers of deaths in migrants were compared with expected numbers based on the age standardised mortality experience of the Finnish Twin Cohort. First deaths in migrants and non-migrants of migrant discordant pairs were compared controlling for genetic and early childhood factors.
Twin pairs of the Finnish Twin Cohort Study where at least one twin had migrated to Sweden (1542 twin pairs).
Among men, migrants from Finland to Sweden showed an overall similar mortality compared with all subjects of the Finnish Twin Cohort (SMR 1.1; 95% CI 0.9 to 1.4). Mortality from non-violent causes was increased for migrants with at most 20 years in Sweden (SMR 1.9; 95% CI 1.2 to 2.6) and decreased in those with a longer stay (SMR 0.7; 95% CI 0.4 to 0.9). Similar results were obtained concerning first deaths in twin pairs discordant for migration. Among women, migrants had an increased mortality overall (SMR 1.4; 95% CI 1.0 to 1.8), from cardiovascular disease (SMR 1.7; 95% CI 1.0 to 2.7), and from violent causes (SMR 2.5; 95% CI 1.2 to 4.6) compared with all women of the Finnish Twin Cohort. In analyses of migrant discordant pairs only first deaths from cardiovascular disease tended to be more common in the migrants than in non-migrant co-twins.
Migrants from Finland to Sweden seem to have an overall mortality comparable to that prevailing in Finland suggesting no strong influence on mortality by the migration. Duration of stay seems to be associated with mortality in the migrants, at least in men, with a lower mortality after several years in Sweden.