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G E McClearn

Publications and source records attributed to G E McClearn.

At least 37 records · Page 2Linked to original sources
PubMed1998

Longitudinal and cross-sectional twin data on cognitive abilities in adulthood: the Swedish Adoption/Twin Study of Aging.

Cross-sequential methods of analysis, designed to separate age and cohort effects, were applied to data from the Swedish Adoption/Twin Study of Aging. Thirteen cognitive variables were collected at 3 times of measurement separated by 3-year intervals. Data were available from 85 individuals from monozygotic (MZ) pairs reared apart, 132 from MZ pairs reared together, 207 from dizygotic (DZ) pairs reared apart, and 178 from DZ pairs reared together (age range at first assessment: 41-84 years). Time x Cohort interactions were found for mean performance on 8 of the measures, revealing stable mean performance in the younger cohorts and longitudinal decreases in mean performance in the older cohorts. Cohort and time effects for total variance were mixed; little evidence was found for increases in variance with age. Age changes and cohort differences in genetic and environmental components of variance were test-specific; several Cohort x Time interactions attained significance. Heritability of the general cognitive ability factor showed significant longitudinal decreases over time in the older cohorts.

Adolescent↗
PubMed1998

Mortality and biomarkers of aging in heterogeneous stock (HS) mice.

A longitudinal study was undertaken to evaluate the relationships among a battery of aging biomarkers and subsequent survival time in 319 genetically heterogenous stock (HS) mice. The biomarker variables chosen were selected from the broad domains of behavior, homeostatic physiology, oxidative defense, and immune function; biomarkers were measured at 45, 90, 360, 630, and 900 days of age. Sex differences were found in the survivor and mortality functions, with a mortality rate crossover occurring at about 525 days and a survival curve crossover at about 750 days of age. Females experienced lower initial mortality but had more sharply increasing mortality with age than did males. Survival analysis using Gompertz parametric models with biomarkers as time-varying covariates yielded significant biomarkers from each domain. Following backward elimination procedures, the final set of independent mortality predictors included headpokes in the File activity apparatus, maximum cord drop time, weight, hematocrit, urine concentration, natural killer cell activity, and concanavalin A response.

6-Ketoprostaglandin F1 alpha↗
PubMed1998

The effect of genetic factors for longevity: a comparison of identical and fraternal twins in the Swedish Twin Registry.

BACKGROUND: The relative importance of genetic influences on longevity was studied on data from the population-based Swedish Twin Registry. METHODS: A sample of 3,656 identical and 6,849 like-sexed fraternal twin pairs was studied regarding mortality rates and within-pair similarity for age at death. Genetic and environmental contributions to variation in longevity, expressed by integrated mortality rates, were estimated from a subsample of 1,734 twin pairs reared together and 130 twin pairs reared apart from the cohorts born 1886 to 1900. RESULTS: The intraclass correlation coefficients suggested that the genetic effect was small, and, for males, perhaps absent. Among pairs in which both twins died relatively young and among pairs in which both twins lived until very old age, the variance in age at death seemed to have no genetic component. Model fitting procedures based on twins reared apart and twins reared together indicated that most of the variance in longevity was explained by environmental factors. CONCLUSIONS: Over the total age range examined, a maximum of around one third of the variance in longevity is attributable to genetic factors, and almost all of the remaining variance is due to nonshared, individual specific environmental factors. The evidence that genetic factors play a minor role depending upon age at death merits further examination.

Adult↗
PubMed1998

Longitudinal and genetic effects in the relationship between pulmonary function and cognitive performance.

Previous studies have found cognitive deficits in patients with impaired pulmonary function, and recent data from healthy older adults suggest an association of pulmonary function with cognitive function. This 6-year longitudinal study evaluated genetic and environmental sources of covariation in the association of pulmonary function and cognitive performance. The sample included 222 Swedish twin pairs (60% women) with a mean age of 62.3 (+/- 7.7) years (age range: 40-84). Hierarchical multiple regression analyses, controlling for the effects of age, gender, and height, were employed to predict performance on cognitive tests of fluid intelligence (Digit Symbol, Block Design, Digit Span-Backward) and crystallized intelligence (Information) from forced expiratory volume in one second (FEV1). Bivariate cross-twin correlations were used to evaluate the contribution of genetic and environmental factors in the association of pulmonary function and cognitive performance. Results indicated that FEV1 predicted performance on tests of fluid intelligence but not crystallized intelligence at the initial assessment and at the 6-year follow-up. Cross-twin correlational analyses indicated that genetic effects accounted for a greater share of the association of pulmonary function and cognitive performance than environmental effects, but environment also accounted for a substantial share of the covariance.

Adult↗
PubMed1998

Confirmation of quantitative trait loci for alcohol preference in mice.

An F2 intercross derived from C57BL/6 and DBA/2 progenitor inbred strains was used to test for replication of quantitative trait loci (QTLs) for alcohol preference nominated by a previous study using BXD recombinant inbred (RI) strains (Rodriguez et al., Alcohol. Clin. Exp. Res. 19:367-379, 1995). Fourteen provisional QTLs were nominated in the original RI study with a p < 0.05 criterion. In the present study, a genome scan (101 microsatellite markers) was conducted on an F2 population (n = 218). Three significant QTLs were detected on chromosomes 1, 4, and 9, and three suggestive QTLs were detected on chromosomes 2, 3, and 10. Of these six QTLs, four were consistent with the previous RI nominations. The replication rate of 28.6% (4 of 14) is in agreement with the results of simulation studies performed by Belknap et al. (Behav. Genet. 26:149-160, 1996) and supports the methodological argument for a multistage research design for nominating and replicating QTLs.

Alcohol Drinking↗
PubMed1997

Substantial genetic influence on cognitive abilities in twins 80 or more years old.

General and specific cognitive abilities were studied in intact Swedish same-sex twin pairs 80 or more years old for whom neither twin had major cognitive, sensory, or motor impairment. Resemblance for 110 identical twin pairs significantly exceeded resemblance for 130 fraternal same-sex twin pairs for all abilities. Maximum-likelihood model-fitting estimates of heritability were 62 percent for general cognitive ability, 55 percent for verbal ability, 32 percent for spatial ability, 62 percent for speed of processing, and 52 percent for memory. There was also evidence for the significant influence of idiosyncratic experience as the environmental component that most determines individual differences in cognitive abilities late in life.

Aged↗
PubMed1997

No association between general cognitive ability and the A1 allele of the D2 dopamine receptor gene.

Berman and Noble (1995) reported significantly reduced visuospatial performance in children with the TAQI A1 allele of the D2 dopamine receptor (DRD2) gene. Given that visuospatial performance loads highly on an unrotated principal component indexing general cognitive ability, we tested the association between DRD2 and WISC-R IQ comparing 51 high-IQ, 51 average-IQ, and 35 low-IQ children in the IQ Quantitative Trait Loci (QTL) Project. No statistically significant association between the TAQI A DRD2 alleles and IQ was found. Given that a statistically significant portion of genetic variance for specific cognitive abilities is independent of general cognitive ability, it is possible that the TAQI DRD2 association is specific to visuospatial performance and independent of general cognitive ability.

Adolescent↗
PubMed1997

Can personality explain genetic influences on life events?

Previous research in the Swedish Adoption/Twin Study of Aging (SATSA) has found genetic influences on life events (R. Plomin, P. Lichtenstein, N.L. Pedersen, G.E. McClearn, & J.R. Nesselroade, 1990). The present study extends this finding by examining sex differences in genetic and environmental contributions to life events and by examining personality as a mediator of genetic influences on life events in SATSA. Analyses were based on 320 twin pairs, including identical and fraternal twins reared together and apart (mean age = 58.6 years). Controllable, desirable, and undesirable life events were revealed significant genetic variance for women. There was no significant genetic variance for either sex for uncontrollable events. Multivariate analyses of personality (as indexed by Neuroticism, Extraversion, and Openness to Experience) and life events suggest that all of the genetic variance on controllable, desirable, and undesirable life events for women is common to personality. Thus, in this sample of older adult women, genetic influences on life events appear to be entirely mediated by personality.

Adult↗
PubMed1997

Genetics and behavioral medicine: risk factors for cardiovascular disease.

This is the second in a series of three articles addressing the intersection of interests in behavioral genetics and behavioral medicine. In this article, we use risk factors for cardiovascular disease as a prototypical trait for which behavioral genetic approaches provide powerful tools for understanding how risk factors, behavior, and health outcomes are related. The approach synthesizes a number of methods and areas of interest in an attempt to arrive at a comprehensive, whole-organism understanding of health-related risk factors and their response to behavioral interventions.

Adolescent↗
PubMed1997

Selection bias in samples of older twins? A comparison between octogenarian twins and singletons in Sweden.

Twin studies are a powerful approach for estimating genetic and environmental influences in later life, but the usual requirement that both twins are alive may introduce a selection bias in gerontological studies relative to representative samples of nontwins. In the present study, samples of older twins and nontwins in Sweden were compared across the domains of vitality, well-being, physical and cognitive functioning, and health utilization to evaluate possible selection bias. One member of each twin dyad in the OCTO-Twin Study of intact twin pairs older than age 80 was randomly selected (N = 128) and compared with a population-based sample of nontwins (N = 324) from the OCTO Study. Multiple regressions adjusting for differences in demographic variables showed significant effects for twin status in only 3 of 20 comparisons. The results suggest that twin pairs surviving into very late life are similar to a representative sample of nontwins of the same age in health status and biobehavioral functioning. These findings support the generalizability of twin studies for understanding genetic and environmental influences on aging, health, and behavior.

Aged↗
PubMed1996

Genetics and behavioral medicine.

Genetics has substantial relevance to behavioral medicine. A rapidly growing body of evidence indicates the influence of genetics on health and disease and on the behavioral factors related to them. The model of quantitative genetics provides a general interpretational scheme for this burgeoning field. The model focuses on variability, and a major research objective is the decomposition of observed individual differences into portions attributable to various types of genetic and environmental sources of variability. This approach emphasizes the coaction of genes and environments and stands in sharp contrast to the archaic view that places nature and nurture in opposition. Some relevant examples are given in this first article to illustrate the general analytic process. A detailed application to cardiovascular health and disease is provided in the second article, and some policy implications are briefly considered in the third article.

Alleles↗
PubMed1996

A co-twin--control study of response to widowhood.

The effects of long-term and recent conjugal bereavement were investigated in a sample of 2,104 Swedish twins followed between 1984 and 1993. In co-twin-control analyses, the bereaved twin experienced significantly more depressive symptoms, more loneliness, and less life satisfaction than the married co-twin. This association existed for recently widowed (< 3 years) of both sexes. Long-term widowed (> 5 years) reported more loneliness than married individuals, and for women there was also a difference in life satisfaction. There were no effects of bereavement on perceived physical health. Individual analyses, which included all respondents regardless of the co-twin's bereavement status, showed the same pattern of results. There was also evidence for an anticipation effect of widowhood indicated by elevated depressive symptoms prior to the spouse's death. Finally, longitudinal analyses showed that it is more stressful to be bereaved when young-old than old-old, but revealed no age differences in adaptation.

Age Factors↗
PubMed1995

Sex distinctiveness in effective genotype.

The difference between sexes in incidence and prevalence of alcohol-related problems is a central feature of alcohol research. It is inevitable that these differences will receive escalating attention as it becomes increasingly apparent that the interests of both equity and good science are served by the study of sex differences in health-related processes. For several reasons, genetic methods promise to offer powerful tools for the elucidation of sex differences. In the first place, the determination of sex depends on a genetic mechanism. Furthermore, there is an abundant literature showing the relevance of heredity to a broad variety of alcohol-related processes. Moreover, there is evidence of major differences in genetic influences in males and females in respect to alcoholism specifically. It is important to appreciate that genetic influence on sex distinctiveness may operate through several different mechanisms, with quite different implications. The purpose of this chapter is to provide an elementary description of these different genetic routes to sex differences.

Alcohol Drinking↗
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

Potential environmental effects on adult lipoprotein(a) levels: results from Swedish twins.

Two hundred and ninety four pairs of Swedish twins reared apart and twins reared together were used to evaluate the importance of genetic and environmental influences on lipoprotein(a) (Lp(a)) levels. Lp(a) levels ranged from <10 mg/l to 926 mg/l with 7.9% of the sample having undetectable Lp(a) levels (i.e. <10 mg/l). A substantial genetic component in Lp(a) variation was indicated by a heritability estimate of approximately 90%. No difference in heritability was found across age groups. Quantitative genetic analyses also suggest correlated environmental effects most likely composed of maternal, neonatal and postnatal environmental influences. However, these effects did not reach statistical significance, partly due to a lack of power. Results from analyses of co-twin differences in Lp(a) levels for monozygotic twins indicate that sex hormone use may be of importance for Lp(a) variation in women. There was no evidence of potential influences of alcohol consumption, beta-blocker and diuretic administration on Lp(a) levels in either men or women.

Aged↗
PubMed1995

Alcohol acceptance, preference, and sensitivity in mice. II. Quantitative trait loci mapping analysis using BXD recombinant inbred strains.

Quantitative trait loci (QTL) mapping of complex phenotypes has emerged as an important feature of the recombinant inbred (RI) strain methodology. In this second study of our series on alcohol-related behaviors in mice, we examine alcohol acceptance, preference, and hypnotic dose sensitivity (HDS) to a standard dose of alcohol measured in BXD RI strains to identify candidate QTL regions responsible for their heritability. We detected highly significant marker associations for acceptance on chromosome 12 (Eif4e), for preference on chromosome 1 (D1Rti2) and chromosome 7 (D7Mit7), and for HDS on chromosome 7 (Mpmv1). These are the strongest QTL associations that we detected, but several other candidate QTL regions are reported. Given the limited number of BXD RI strains available, the large number of markers used herein, and the consequent chance of identifying false marker associations, these RI QTL mapping results must be seen as tentative, but an important first step toward identifying QTL for alcohol-related behaviors.

Alcohol Drinking↗
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↗