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.
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.
In a specific case, the magnetic field generated in a building by a nearby power line is usually easy to calculate, although the accuracy of these calculations is sensitive to the quality of source information. To be able to study public health dimensions of magnetic field exposure (e.g., risk of cancer), it is necessary to evaluate the size and exposure of the population at risk. Relatively little quantitative information on public exposure to power-frequency magnetic fields of high-voltage power lines is available. This report describes residential exposure to magnetic fields from 110 kV, 220 kV, and 400 kV power lines in Finland at the national level, including 90% of the total line length in 1989. A geographical information system (GIS) was used to identify the buildings located near the power lines. After determining the distances between the lines and the buildings, historical data on load currents of these lines were used to calculate the magnetic fields. The residential magnetic field histories were then linked to the residents by means of a computerized central population register. The data obtained on personal exposure have also been utilized in a nationwide epidemiological study on magnetic field exposure of power lines and risk of cancer. The methods of exposure assessment and results of the number of buildings near 110 kV, 220 kV, and 400 kV power lines, their average annual magnetic fields, and personal exposure to magnetic fields from these lines are described. We found that 15,600 residents lived in an average residential magnetic field > or = 0.1 microT caused by power lines in 1989. The number of these residents increased fivefold during 1970-1989. We estimated that 0.3% of the population was exposed in their residences to an annual average magnetic flux density from 110 kV, 220 kV, and 400 kV power lines higher than 0.1 microT, the level that the background magnetic flux density in general does not exceed in Finnish homes. Thus, the problem of magnetic field exposure generated by high-voltage lines concerns only a relatively small fraction of the total population in Finland. However, the size and exposure of the population at risk remain somewhat arbitrary in practical multisource situations, as the biological interaction mechanism, the concept of harmful dose, and, in particular, the significance of the duration of exposure are unknown.
The relative roles of genetic and environmental factors in bruxism are not known. 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 bruxism. There was a significant gender difference both in childhood (P = 0.001) and adult (P = 0.007) bruxism. Females compared to males reported childhood bruxism 'often' 5.2% vs 4.1% and 'sometimes' 17.4% vs 17.3%, and as adults 'weekly' 3.7% vs 3.8% and 'monthly' 3.9% vs 4.6%, respectively. Bruxism in childhood and adulthood is highly correlated (0.86 in males and 0.87 in females). The proportion of total phenotypic variance in liability to bruxism attributed to genetic influences in childhood bruxism was 49% (95% CI 37-60%) in males and 64% (55-71%) in females, and for adults 39% (27-50%) among males and 53% (44-62%) among females. The correlation between the genetic effects on childhood bruxism and the genetic effects on adult bruxism was estimated in a bivariate model to be 0.95 (95% CI 0.94-0.96) in males and 0.89 (0.88-0.90) in females. Bruxism appears to be quite a persistent trait. There are substantial genetic effects on bruxism both in childhood and as adults, which appear to be highly correlated.
The relative roles of genetic and environmental factors in sciatica were studied in the nationwide Finnish twin panel consisting of 9365 adult pairs of the same gender. Morbidity was analysed from two sources of data: the life-long cumulative incidence was measured by a postal questionnaire, and the rate of hospital admission during a 14-year period was measured by record-linkage of the twin panel and the nationwide hospital registry. Altogether 2220 individuals reported sciatica diagnosed by a doctor and 304 were admitted to hospital with a diagnosis of sciatica. The proportion of concordant pairs (calculated from affected pairs) was 17.7% for monozygotic and 12.0% for dizygotic pairs in the life-long cumulative incidence of reported sciatica, and correspondingly 4.6% and 1.9% for those admitted to hospital (a 14-year period) because of sciatica. The estimated heritability was 20.8% for those with reported sciatica and 10.6% for those admitted to hospital. The results show that environmental factors account for more than 80% of the etiology of sciatica, and more than 90% in the case of patients admitted to the hospital. Genetic factors, however, were relatively more significant in individuals under 40.
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.
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.
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.
To investigate the risk of cancer in association with magnetic fields in Finnish adults living close to high voltage power lines.
Nationwide cohort study.
383,700 people who lived during 1970-89 within 500 metres of overhead power lines of 110-400 kV in a magnetic field calculated to be > or = 0.01 microT. Study subjects were identified by record linkages of nationwide registers.
Numbers of observed and expected cases of cancer, standardised incidence ratios, and incidence rate ratios adjusted for sex, age, calendar year, and social class--for example, by continuous cumulative exposure per 1 microT year with 95% confidence intervals from multiplicative models for all cancers combined and 21 selected types.
Altogether 8415 cases of cancer were observed (standardised incidence ratio 0.98; 95% confidence interval 0.96 to 1.00) in adults. All incidence rate ratios for both sexes combined were non-significant and between 0.91 and 1.11. Significant excesses were observed in multiple myeloma in men (incidence rate ratio 1.22) and in colon cancer in women (1.16).
Typical residential magnetic fields generated by high voltage power lines do not seem to be related to the risk of overall cancer in adults. The previously suggested associations between extremely low frequency magnetic fields and tumours of the nervous system, lymphoma, and leukaemia in adults and breast cancer in women were not confirmed.
Cites: Br J Ind Med. 1985 Mar;42(3):211-23970890
Cites: Br J Ind Med. 1985 Aug;42(8):546-504016006
Cites: Cancer Res. 1986 Jan;46(1):239-442998606
Cites: Br J Cancer. 1986 Feb;53(2):271-93456788
Cites: Am J Epidemiol. 1987 Apr;125(4):556-613548332
Cites: Ann N Y Acad Sci. 1987;502:43-543310802
Cites: Am J Epidemiol. 1988 Jul;128(1):10-203381818
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.
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.
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.
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.
Cites: Am J Epidemiol. 1988 Jul;128(1):21-383164167
Cites: BMJ. 1993 Oct 9;307(6909):891-58241850
Cites: Am J Epidemiol. 1979 Mar;109(3):273-84453167
Cites: Am J Epidemiol. 1980 Mar;111(3):292-67361752
Cites: Am J Epidemiol. 1980 Apr;111(4):461-27377191
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.
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.