Biomedical subjects

N L Pedersen

Publications and source records attributed to N L Pedersen.

At least 91 records · Page 5Linked to original sources

PubMed1996

Origins of individual differences in anxiety proneness: a twin/adoption study of the anxiety-related scales from the Karolinska Scales of Personality (KSP).

The genetic and environmental origins of individual differences in scores on the anxiety-proneness scales from the Karolinska Scales of Personality were explored using a twin/adoption study design in a sample consisting of 15 monozygotic twin pairs reared apart, and 26 monozygotic and 29 dizygotic twin pairs reared together. The results showed that genetic factors accounted for individual differences in scores on the psychasthenia and somatic anxiety scales. The genetic determinants were not specific to each scale, but were common to both scales. Shared-rearing environmental determinants were important for individual differences in lack of assertiveness and psychic anxiety, and were common to both scales. Individual differences in muscular tension were found to be attributable to the effects of correlated environments. The most important factor explaining individual differences for all scales was the non-shared environment component. The evidence for an aetiologically heterogeneous anxiety-proneness construct emphasizes the appropriateness of a multi-dimensional approach to anxiety proneness.

Adult↗

PubMed1996

Physical and mental health related to dental amalgam fillings in Swedish twins.

In the past years increasing attention has been paid to possible adverse health effects of mercury exposure from dental amalgam fillings. To evaluate possible health effects from amalgam fillings, dental status registered by specially trained nurses was obtained from 587 subjects included in the ongoing Swedish Adoption/Twin Study of Aging (SATSA). Data on physical and mental health were collected and memory function tested. Mean age was 66 years (SD 9, range 46-89). In the entire material, 25% of the individuals had no own teeth and in the group with own teeth the median number of teeth surfaces filled with dental amalgam was 15 (range 0-65). Analyses of associations between number of surfaces filled with dental amalgam and a number of scales estimating somatic and mental health and memory functions were performed both for the entire group and for individuals having at least 12 teeth. Regardless of the sample, no negative effects on physical or mental health were found from amount of dental amalgam, even after controlling for age, gender, education and number of remaining teeth. When using a co-twin control design with twin pairs discordant for amalgam exposure, no negative health effects associated with dental amalgam were detected. This study does not indicate any negative effects from dental amalgam on physical or mental health or memory functions in the general population over 50 years of age.

Age Factors↗

PubMed1996

Quantitative genetic analyses of insulin-like growth factor I (IGF-I), IGF-binding protein-1, and insulin levels in middle-aged and elderly twins.

With the use of quantitative genetic models, the relative importance of genetic and environmental influences on serum levels of insulin-like growth factor I (IGF-I), IGF-binding protein-1 (IGFBP-1), and insulin was evaluated in 248 pairs of middle-aged and elderly Swedish twins reared apart and reared together. Heritability estimates (the relative influence of genetic effects) were 48% for insulin, 63% for IGF-I, and 36% for IGFBP-1. There was no indication of differences in heritability estimates for IGF-I, IGFBP-1, and insulin across age and gender groups. Nonshared environmental influences, unique to individuals, explained the remaining variance in the measures. The genetic influences on IGF-I levels were independent of the genetic influences on insulin and IGFBP-1 levels. However, a small, but significant, proportion of the genetic variation in IGFBP-1 was in common with genetic influences for insulin. Furthermore, genetic effects explained 36% of the phenotypic correlation between IGFBP-1 and insulin, whereas the phenotypic associations between IGF-I and both IGFBP-1 and insulin were entirely attributable to environmental effects. Finally, the phenotypic association between IGF-I and IGFBP-1 was mediated wholly by environmental influences in common with insulin.

Aged↗

PubMed1995

A pilot Swedish twin study of affective illness including hospital- and population-ascertained subsamples: results of model fitting.

We investigated the heritability of liability to affective illness (AI) in twins ascertained through psychiatric hospitalization for AI from the Swedish Psychiatric Twin Registry and from the general population Swedish Twin Registry. Lifetime diagnoses were assessed by mailed questionnaire containing, in self-report format, DSM-III-R criteria for mania and major depression (MD). Jointly analyzing both subsamples using Mx, and assuming a multifactorial threshold model, the best-fitting twin model using narrow diagnostic criteria suggested that the liability to AI could be explained by additive genetic effects, with an estimated heritability of liability of 64%, and individual-specific environment. Using broad criteria, results were similar except that the estimated broad heritability of liability was higher (83%) and due largely to dominance genetic effects. Fitting sex-dependent models suggested that the same genetic and environmental factors influenced liability to AI in men and women to the same degree, although women had a lower threshold of manifestation. These results suggested that in Sweden, AI is a highly heritable syndrome and family resemblance is due largely or entirely to genetic factors.

Adult↗

PubMed1995

Heritability of cognitive abilities in adult twins: comparison of Minnesota and Swedish data.

Cross-sectional reports suggest heritability of cognitive ability increases throughout adulthood. To investigate this hypothesis, quantitative genetic analyses were conducted on four measures of cognitive ability (verbal, spatial, perceptual speed, memory). Data from Minnesota and Swedish twin studies of aging were compared. Heritability estimates and the factor structure of cognitive abilities could be equated across younger twins (age, 27-50) and middle-aged twins (age, 50-65) from both studies, suggesting stability of heritability during adulthood. The heritability of 81% for a general cognitive factor confirmed earlier findings of high heritability in younger and middle-aged samples. Older Swedish twins (age, 65-85) demonstrated significantly lower heritability estimates for cognitive abilities (54%) and a significantly different factor structure of cognitive ability.

Adult↗

PubMed1995

Dimensions of occupations: genetic and environmental influences.

This study investigates the dimensions of occupation, and distances between occupational categories, by using intra-pair differences in adult occupational position for identical twins reared apart. Status and farm dimensions of occupation were identified. The results validate the use of occupational status as a dimension of occupational position. The causes of individual differences for the derived status dimension were also evaluated, based on groups of identical and fraternal twins reared apart or together. Genetic effects accounted for a substantial amount of the variance in occupational status for men, while shared and non-shared environmental effects were of about equal importance. For women, genetic effects were less important, and shared and non-shared environmental effects accounted for more of the variation. The results confirm that genetic effects are important sources of the familial resemblance often found for occupational status for men.

Adoption↗

PubMed1995

A twin study of generalized anxiety disorder and major depression.

Previous analyses with a sample of female twins sampled from the general population in Virginia have suggested that generalized anxiety disorder (GAD) and major depression (MD) share their genetic determinants but have partly different environmental determinants. The goal of this report is to examine whether these findings apply to samples that include male as well as female twins and contain high proportions of subjects who had been hospitalized for MD. The subjects were ascertained through two different sources: (i) index probands were ascertained through the Swedish Psychiatric Twin Registry for a diagnosis of unipolar or bipolar affective illness; (ii) control twin probands were ascertained through the Swedish Twin Registry. Subjects were sent questionnaires for the assessment of lifetime history of GAD and MD. Positing multinormal distribution of the liability for GAD and MD, we fitted bivariate models to examine the sources of comorbidity. The full model included additive genetic effects, shared environment and individual-specific environment, as well as scalar and non-scalar sex limitations and different thresholds across genders. The best-fitting model included: (i) a genetic correlation of unity; (ii) no common environment; (iii) an individual-specific environmental correlation of 0.28; (iv) different thresholds across genders, but neither scalar nor non-scalar sex-limitations. A model that included additive and dominant genetic effects and individual-specific environment, with correlation of unity for both additive and dominant genetic effects, provided an equivalent fit. These analyses confirm that GAD and MD share the same genetic factors but that their environmental determinants are mostly distinct. Moreover, the present report supports the feasibility of combining clinical ascertained and general-population samples into a single bivariate analysis.

Adult↗

PubMed1995

Traits and metatraits: their reliability, stability, and shared genetic influence.

Metatraits measure individual differences in construct relevancy, whereas traits measure individual differences in construct extremity. Twenty-four traits and metatraits were examined in this study using 157 pairs of identical twins reared together, 95 pairs of identical twins reared apart, 211 pairs of fraternal twins reared together, and 228 pairs of fraternal twins reared apart obtained from the Swedish Adoption/Twin Study of Aging (see N. L. Pedersen et al., 1991). Reliability and stability analyses of the metatraits revealed generally lower reliability and stability across time compared to traits. Quantitative genetic analyses of the relationship between traits and metatraits indicated that approximately 69% of the metatrait's genetic variance is shared with the trait, with 31% of its genetic variance unique to the metatrait. These results suggest that metatraits provide a useful additional view of personality.

Adoption↗

PubMed1995

Genetic influence in headaches: a Swedish twin study.

The heritability of liability to self-reported migraine and nonmigrainous headaches was examined in two large cohorts from the Swedish Twin Registry consisting of 6448 (the older cohort) and 12,884 (the younger cohort) like-sexed twin pairs. Higher concordance rates were consistently found for lifetime migraine among the monozygotic twins than in the dizygotic twins, as well as for migraine headaches of the recurrent disabling type. In addition, a higher concordance rate was found among the monozygotic twins than in dizygotic twins in a "mixed" group of possible tension-type or mild migraine headaches (or both). The results of structural equation model-fitting analyses showed that genetic effects for migraine headaches were stronger for the females (estimates ranging from 49% to 58%) than for the males (39% to 44%) in the two cohorts. Unique nonshared environmental effects were greatest for the "mixed" group in both sexes (estimates ranging from 60% to 69%). The results are discussed in view of similar large-scale twin studies examining the heritability of liability to migraine.

Adolescent↗

PubMed1995

Apolipoprotein epsilon 4 allele in Swedish twins and siblings with Alzheimer disease.

Allelic frequencies of apolipoprotein epsilon 4 were compared in 13 dizygotic twin pairs and 13 sibling pairs in which at least one member has Alzheimer disease (AD). Among discordant pairs of twins and siblings, frequencies were significantly greater in affected than intact partners. There was no significant difference in allelic frequencies between twins with a positive family history and twins with a negative family history. The epsilon 4 allele was more common in the sibling sample selected for family aggregation of AD than the twin sample. Several lines of evidence indicate that while the epsilon 4 allele appears to be one risk factor for AD, other etiological factors must be considered as well.

Aged↗

PubMed1994

Helicobacter pylori infection: genetic and environmental influences. A study of twins.

OBJECTIVE: To investigate the importance of genetic effects for acquiring Helicobacter pylori infection. DESIGN: Cross-sectional study on monozygotic and dizygotic twins, reared apart and reared together. SETTING: Twins from a subregistry of the Swedish Twin Registry, which includes entries for about 25,000 twin pairs who were born in Sweden. MEASUREMENTS: Helicobacter pylori status was assessed as the presence of anti-H. pylori IgG in 269 pairs of twins, including 36 monozygotic twin pairs reared apart, 64 monozygotic twin pairs reared together, 88 dizygotic twin pairs reared apart, and 81 dizygotic twin pairs reared together. RESULTS: The probandwise concordance rate for H. pylori infection was higher in monozygotic twin pairs (81%) than in dizygotic twin pairs (63%) (P = 0.001). Probandwise concordance rates for H. pylori infection among 124 pairs of twins reared apart were 82% and 66% for monozygotic and dizygotic twins, respectively (P = 0.003). The correlation coefficient was 0.66 for monozygotic twins reared apart, and it provides the best single estimate of the relative importance of genetic effects (heritability) for variation in the acquisition of H. pylori infection. The heritability estimate from model-fitting analyses was 0.57, a similar result. The remaining variance was accounted for by shared rearing environmental (20%) and nonshared environmental factors (23%). The latter contribute to differences, not similarities, among family members. CONCLUSION: This twin study showed that genetic effects influence the acquisition of H. pylori infection because of greater similarities within the monozygotic twin pairs. Further, sharing the same rearing environment also contributes to the familial tendency for acquiring H. pylori infection.

Chi-Square Distribution↗

PubMed1994

Variability and stability in cognitive abilities are largely genetic later in life.

The powerful quantitative genetic design of identical and fraternal twins reared apart (112 pairs) and matched twins reared together (111 pairs) was employed to assess the extent of genetic influence on individual differences in cognitive abilities during the last half of the life span. General cognitive ability yielded a heritability estimate of about .80 in two assessments 3 years apart as part of the Swedish Adoption/Twin Study of Aging. This is one of the highest heritabilities reported for a behavioral trait. Across the two ages, average heritabilities are about .60 for verbal tests, .50 for spatial and speed-of-processing tests, and .40 for memory tests. For general cognitive ability, the phenotypic stability across the 3 years is .92 and stable genetic factors account for nearly 90% this stability. These findings suggest that general cognitive ability is a reasonable target for research that aims to identify specific genes for complex traits.

Aging↗

PubMed1994

Genetic and environmental influences on pulmonary function in aging Swedish twins.

BACKGROUND: In addition to their value in assessing pulmonary health and disease, spirometric variables have been shown to be powerful predictors of time until death in aging populations. The sources of variability in these spirometric values are consequently of relevance to basic gerontological research, and also of potential value in clinical application. The objective of this study was to estimate genetic and environmental sources of variance in pulmonary function. METHODS: The study involved 230 Swedish twin pairs (mean age = 64.9 years), of which number 37 monozygotic (MZ) pairs and 72 dizygotic (DZ) pairs had been separated and reared apart. Comparing these groups to the 57 MZ and 64 DZ pairs reared together permits stronger interpretation than that of conventional twin studies. Measures of vital capacity (VC) and forced expiratory volume in one second (FEV1) were residualized for height, age, sex, and tobacco consumption in pack-years. RESULTS: Maximum likelihood analyses of VC and FEV1 gave heritability estimates of .48 and .67, respectively. Age effects were explored both by dividing the sample into two cohorts, respectively above and below 65 years, and by moving interval analysis. In the two-cohort analysis, heritabilities were somewhat higher for the older cohort than the younger cohort for FEV1. The opposite was true for VC: heritability was lower in the older cohort, and there was evidence for a shared rearing environmental effect for this group. Moving interval analysis suggests these differences are gradual rather than saltatory. There were no gender differences in parameter estimates. CONCLUSION: Genetic factors account for between one-half and two-thirds of the variability in pulmonary function. There is a suggestion of age differences in the relative importance of genetic and environmental influences.

Adult↗

PubMed1994

Genetic and environmental correlations among serum lipids and apolipoproteins in elderly twins reared together and apart.

Genetic and environmental correlations among five serum-lipid measures were examined in the Swedish Adoption/Twin Study of Aging. The sample included 302 twin pairs; 146 of these twin pairs were separated at an early age and were reared apart. The lipid measures examined include total cholesterol, HDL-cholesterol, triglycerides, and apolipoproteins A-I and B. Genetic and environmental correlations were evaluated for two different age groups, formed by dividing the sample at the median. The younger group included individuals 41.8-65.4 years of age at the midpoint of testing, although only 24 individuals were < 50 years of age. The older group included all those > 65.4 years of age, up to age 87 years of age. Substantial genetic correlations were found within each age group, although there is no evidence for a single genetic factor common to all five lipids. The comparison of twins reared together with twins reared apart allowed estimation of the effects of shared rearing environment; however, shared rearing environment only appears to be a significant mediator of the phenotypic correlation between apolipoprotein B and cholesterol in the older group. Examination of the genetic and environmental covariances suggests that the relative contributions of genetic factors are lower in the older group. Nonshared environmental factors are relatively more important mediators of phenotypic correlations among the serum lipids in individuals > 65.4 years of age than they are for the younger group. Sex differences in the mediation of these serum lipids were not as clear.

Adult↗

PubMed1993

Genetic and environmental influences on serum lipid levels in twins.

BACKGROUND: The extent to which serum lipid levels are affected by genetic and environmental factors remains a point of controversy. We examined both genetic and environmental influences on serum lipid levels in twins reared either together or apart who participated in the Swedish Adoption/Twin Study of Aging. METHODS: We studied 302 pairs of twins (mean age, 65.6 years; range, 52 to 86); 146 pairs had been reared apart. We simultaneously compared the twins on the basis of both zygosity and rearing status, which allowed joint estimation of genetic and environmental influences on serum lipid levels. Genetic influence was expressed in terms of heritability, the proportion of the population variation attributable to genetic variation (a value of 1.0 indicates that all of the population variation is attributable to genetic variation). The serum lipids and apolipoproteins measured included total cholesterol, high-density lipoprotein cholesterol, apolipoproteins A-I and B, and triglycerides. RESULTS: Structural-equation analyses revealed substantial heritability for the serum levels of each lipid measured, ranging from 0.28 to 0.78. Comparisons of the twins reared together with those reared apart suggested that the environment of rearing had a substantial impact on the level of total cholesterol (accounting for 0.15 to 0.36 of the total variance). Sharing the same environment appeared to affect the other lipid measures much less, however, than did genetic factors and unique environmental factors not shared by twins. Comparisons of younger with older twins suggested that heritability for apolipoprotein B and triglyceride levels decreased with age. CONCLUSIONS: The effect of genetic factors on the serum levels of some but not all lipids appears to decrease with age. Early rearing environment appears to remain an important factor in relation to levels of total cholesterol later in life, but it has less effect on other serum lipids and apolipoproteins in the elderly.

Age Factors↗

PubMed1993

Importance of genetic effects for monoamine oxidase activity in thrombocytes in twins reared apart and twins reared together.

The relative importance of shared genes, shared environments, and individual specific environmental effects for monoamine oxidase (MAO) activity in thrombocytes was assessed in the Swedish Adoption/Twin Study of Aging. The sample consists of identical twins separated at an early age and reared apart (30 pairs), identical twins reared together (60 pairs), fraternal twins reared apart (66 pairs), and fraternal twins reared together (68 pairs), whose average age was 63.5 years; 49% were female. Consistent with the literature, the heritability of MAO activity was 0.77 and did not differ across cohort (under or over 63 years of age) or gender. Sharing rearing environments or similar experiences later in life does not result in familial similarity for MAO activity.

Adoption↗

PubMed1993

Socioeconomic status and physical health, how are they related? An empirical study based on twins reared apart and twins reared together.

This investigation used the powerful combined twin and adoption design to assess the validity of three different hypotheses--social causation, childhood experiences, and health selection--on the origin of the association between socioeconomic status (SES) and health. The sample contains 99 pairs of monozygotic twins reared apart, 166 pairs of monozygotic twins reared together, 238 pairs of dizygotic twins reared apart, and 221 pairs of dizygotic twins reared together, who completed questionnaire items concerning their SES and health status. Genetic effects, environmental effects unique to the individual, as well as environmental effects shared by twins were involved in mediating the associations between SES and health. However, the relative importance of these effects varied for the different associations depending on the measures of health and SES respectively. The results indicate that social causation, childhood experiences, and health selection may all be important for the association between SES and health. It is argued that these hypotheses are not contradictory, rather the relationship between the complex dimensions SES and health may be explained by several different causes.

Adult↗

PubMed1993

Genetic and environmental effects on openness to experience, agreeableness, and conscientiousness: an adoption/twin study.

Previous research has indicated that extraversion and neuroticism are substantially affected both by genotype and environment. This study assesses genetic and environmental influences on the other three components of the five-factor model of personality: Openness to Experience, Agreeableness, and Conscientiousness. An abbreviated version of the NEO Personality Inventory (NEO-PI) was administered to 82 pairs of identical twins and 171 pairs of fraternal twins reared apart and 132 pairs of identical twins and 167 pairs of fraternal twins reared together. Estimates of genetic and environmental effects for Openness and Conscientiousness were similar to those found in other studies of personality: Genetic influence was substantial and there was little evidence of shared rearing environment. Results for Agreeableness were different: Genetic influence accounted for only 12% of the variance and shared rearing environment accounted for 21% of the variance. Few significant gender or age differences for genetic and environmental parameters were found in model-fitting analyses.

Adoption↗