PubMed Health⌕ Search

Biomedical subjects

G E McClearn

Publications and source records attributed to G E McClearn.

At least 19 recordsLinked to original sources
PubMed1992

The reliability and stability of biomarkers of aging.

Different types of stability of a biomarker are important properties, influencing the degree of predictability across age (ordinal stability) and the interpretation of quantitative and qualitative change with age (structural stability). These properties may be expected to differ from biomarker to biomarker and may change with age. Any age-related process with individual differences in time of onset of change or in rate of change will necessarily display reduced ordinal stability. Another source of reduced correlation across occasions is the short-term fluctuance of individuals due to cyclic processes and to responsiveness to environmental displacements of biomarker values and recovery therefrom. Structural stability of composite variates may be quite high across relatively short intervals but sufficiently low across longer intervals as to suggest the inappropriateness of simple description of mean changes or differences across these longer time spans. The outcome with multivariate composites raises the issue that single biomarkers may have quite different meanings at different parts of the life span.

Aging↗
PubMed1992

Single-locus control of saccharin intake in BXD/Ty recombinant inbred (RI) mice: some methodological implications for RI strain analysis.

The sac locus, with a major effect on saccharin preference, was discovered by Fuller (1974) in C57BL/6J (B6), DBA/2J (D2), and derived crosses, and is now supported in the BXD/Ty recombinant inbred (RI) series by a marked bimodal distribution in saccharin preference among 20 strains. The B6 allele led to increased saccharin preference compared to the D2 allele. Since the search for bimodal distributions reflecting major gene loci is an essential part of RI strain analysis, a new statistical method is proposed to test for bimodality, and comparisons are made to previously proposed methods. Another new RI method, quantitative trait loci (QTL) analysis, allows provisional detection and mapping of minor as well as major gene loci. Using this method as a screen, significant associations with saccharin preference were suggested with marker loci on portions of six chromosomes. One of these, the D12nyu1 locus on chromosome 12, was independently supported in a panel of standard (non-RI) inbred strains also tested for saccharin preference. It is unclear whether this reflects the sac locus.

Animals↗
PubMed1992

The use of CXB recombinant inbred mice to detect quantitative trait loci in behavior.

Although recombinant inbred (RI) series of mice have been developed to identify and map single-gene characteristics, they can also be used to identify quantitative trait loci (QTL) that account for small amounts of variance in quantitative traits such as behavior. We applied an RI QTL approach to the analysis of published behavioral data from seven studies that used the CXB RI series of mice. Nearly all of the behaviors showed strain distribution patterns indicative of multiple-gene rather than single-gene influence. Although the CXB series is limited to seven RI strains, RI QTL association analysis suggests QTL candidate markers for several behaviors, including avoidance and exploration.

Animals↗
PubMed1992

Importance of shared genes and shared environments for symptoms of depression in older adults.

The Center for Epidemiologic Studies-Depression scale was administered to 68 identical and 161 fraternal twin pairs reared apart and 114 identical and 138 fraternal pairs reared together to ascertain relative genetic and environmental contributions to individual differences in self-reported depressive symptoms. Intraclass correlations and model fitting indicated that genetic influences explained 16% of the variance in total depression scores and 19% for the Psychomotor Retardation and Somatic Complaints subscale, but heritability was minimal for the Depressed Mood and Well-Being subscales. Influence of family rearing context played a substantial role in explaining twin similarity, whereas unique life experiences accounted for the greatest proportion of variance. Significant age group differences were observed, with heritability greater in twins of 60 years of age or older than in twins under 60, especially for Psychomotor Retardation.

Adoption↗
PubMed1992

A longitudinal genetic study of tail tendon fibre break time.

Tail tendon fibre break time (TTFBT), an indicator of collagen cross-linkage, was measured longitudinally in C57BL/6, DBA/2 and B6D2F1 mice, and F2 and backcross genotypes. TTFBT was assessed at 50, 150, 300 and 450 days of age. The distribution of means of these six genotypes suggests substantial genetic influence on this phenotype. Broad sense heritability, as assessed in a classical biometrical analysis, was negligible at 50 and 150 days, but accounted for between 25 and 43% of the variance at 300 to 450 days. The stability and reliability of TTFBT were also examined. Reliability was extremely high for each occasion; stability increased from moderate to substantial levels with increasing age, and may be influenced by heterozygosity.

Aging↗
PubMed1992

Age differences in genetic and environmental influences for health from the Swedish Adoption/Twin Study of Aging.

This cross-sectional study explored the etiology of variability in self-reported health. The sample comprises adult twins participating in the Swedish Adoption/Twin Study of Aging and includes identical (MZ) and fraternal (DZ) twin pairs who have been reared together or reared apart. Two different components of overall health status are analyzed: an index of chronic health problems and self-rated health. Height and weight were included to assess the representativeness of the twin data. Individual differences increased across age for both measures of health, and there were significant age differences in the genetic and environmental etiologies of this variation. Genetic variance showed a twofold increase for chronic illness up until age 70. Environmental influences during adulthood appear important later in life. For self-rated health, genetic effects were important in the older age groups; however, the increase in total variation is predominantly due to unique environmental influences.

Adoption↗
PubMed1991

Use of recombinant inbred strains to detect quantitative trait loci associated with behavior.

Recombinant inbred (RI) strains are valuable not only for detecting major gene segregation and linkage but also for identifying associations between behavior and quantitative trait loci (QTL) that account for relatively small amounts of variation in behaviors for which strain distribution patterns are not bimodal. When applied to published data on genetic markers and on behavior for BXD RI strains, the RI QTL association approach suggests the presence of QTLs on chromosomes 6 and 12 for open-field activity and on chromosomes 1, 2, and 17 for high-pressure seizure susceptibility. Because the RI QTL approach does not require that the progenitor inbred strains of a particular RI series differ, researchers could focus on the BXD RI series, for which the greatest number of genetic markers are available. Focusing on BXD would capitalize on the cumulative nature of RI research which permits analyses of QTL sources of genetic correlations across studies.

Acoustic Stimulation↗
PubMed1991

Use of recombinant inbred strains to identify quantitative trait loci in psychopharmacology.

Unlike simple Mendelian characteristics, individual differences in complex quantitative phenotypes studied in psychopharmacology are generally distributed continuously and are likely to be influenced by many genes. Recombinant inbred (RI) strains are valuable not only for their traditional use of detecting major gene segregation and linkage but also for identifying associations between quantitative traits and quantitative trait loci (QTL) that account for relatively small amounts of variation in phenotypes as well as loci that account for greater amounts of variation. When applied to published data on genetic markers and on amphetamine, alcohol, and morphine responses in BXD RI strains (RI strains developed from the cross between C57BL/6J and DBA/2J progenitor inbred strains), the RI QTL approach identified several significant associations beyond known major gene effects. Together, significant associations explain more than half of the genetic variance for these measures. The RI QTL approach is especially valuable for investigating the QTL underpinnings of genetic correlations among measures. It is recommended that psychopharmacogenetic research focus on the BXD RI strains. The cumulative and integrative nature of such a program of research is the major benefit of the RI QTL association approach for molecular genetic analysis of psychopharmacological processes, their physiological infrastructure, and their interface with other behavioral and biological systems.

Animals↗
PubMed1991

The Swedish Adoption Twin Study of Aging: an update.

The Swedish Adoption/Twin Study of Aging (SATSA) is a longitudinal program of research in gerontological genetics which is currently in its fifth year. The base population is comprised of 351 pairs of twins reared apart and 407 matched control pairs of twins reared together who responded to a questionnaire (Q1) in 1984. Two additional stages of SATSA have recently been completed: a longitudinal follow-up questionnaire mailed out in 1987 (Q2) and extensive in-person testing (IPT1) which included a health examination and cognitive battery. A second wave of IPT was started in January 1989. A summary of some of the major findings from Q1 and a description of IPT1 are reported.

Adoption↗
PubMed1991

Genetic mediation of the relationship between social support and psychological well-being.

This study assessed genetic and environmental influences on the association between social support and psychological functioning using the combined adoption/twin design from the Swedish Adoption/Twin Study of Aging. A subsample of 424 twin pairs, 50 years and older, was used: 64 pairs of identical twins reared apart, 95 pairs of identical twins reared together, 132 pairs of fraternal twins reared apart, and 133 pairs of fraternal twins reared together. Multivariate model-fitting analyses indicated that the relationship between the perceived adequacy of social support and psychological well-being (depression and life satisfaction) was mediated in part by genetic factors.

Adaptation, Psychological↗
PubMed1990

The body-mass index of twins who have been reared apart.

To assess the relative importance of genetic and environmental effects on the body-mass index (weight in kilograms divided by the square of the height in meters), we studied samples of identical and fraternal twins, reared apart or reared together. The samples consisted of 93 pairs of identical twins reared apart, 154 pairs of identical twins reared together, 218 pairs of fraternal twins reared apart, and 208 pairs of fraternal twins reared together. The intrapair correlation coefficients of the values for body-mass index of identical twins reared apart were 0.70 for men and 0.66 for women. These are the most direct estimates of the relative importance of genetic influences (heritability) on the body-mass index, and they were only slightly lower than those for twins reared together in this and earlier studies. Similar estimates were derived from maximum-likelihood model-fitting analyses--0.74 for men and 0.69 for women. Nonadditive genetic variance made a significant contribution to the estimates of heritability, particularly among men. Of the potential environmental influences, only those unique to the individual and not those shared by family members were important, contributing about 30 percent of the variance. Sharing the same childhood environment did not contribute to the similarity of the body-mass index of twins later in life. We conclude that genetic influences on body-mass index are substantial, whereas the childhood environment has little or no influence. These findings corroborate and extend the results of earlier studies of twins and adoptees.

Aged↗
PubMed1990

Genetic influence on life events during the last half of the life span.

Genetic influence on perceptions of major events later in life was assessed with a combination of twin and adoption designs as part of the Swedish Adoption/Twin Study of Aging (SATSA). The SATSA design includes 4 groups totaling 399 pairs of same-sex twins: identical and fraternal twins reared apart and matched twins reared together. The average age of the twins was 59 years. The results demonstrate significant genetic influence on reports of the occurrence of life events, especially for controllable events in which the individual can play an active role. Maximum likelihood model-fitting estimates of genetic influence indicate that 40% of the variance of the total life events score is due to genetic differences among individuals. How genetic factors can affect life experiences and directions for future research are discussed.

Humans↗
PubMed1990

Genetic and environmental influences on social support: the Swedish Adoption/Twin Study of Aging.

A new direction in behavioral genetic research is the exploration of genetic influences on ostensibly environmental measures. The goal of the present study was to identify genetic as well as environmental influences that contribute to an individual's motivation and ability to create and maintain social support systems during the second half of the life course. One of the most powerful behavioral genetic designs is the combined twin/adoption design which is used in the Swedish Adoption/Twin Study of Aging (SATSA). A subsample of 424 pairs of twins age 50 and above was used: 64 pairs of identical twins reared apart, 95 pairs of identical twins reared together, 132 pairs of fraternal twins reared apart, and 133 pairs of fraternal twins reared together. The measure of social support assessed both the quantity of relationships as well as the perceived adequacy of the social support network. Model-fitting analyses verified the importance of genetic factors for perceived adequacy of the social support network, whereas little genetic influence was found for the quantity of social relationships.

Adoption↗
PubMed1989

Individual differences in locus of control during the second half of the life span for identical and fraternal twins reared apart and reared together.

The relative influences of genetic and environmental factors for components of locus of control (LOC) were examined in the Swedish Adoption/Twin Study of Aging. The sample consisted of 84 pairs of monozygotic twins separated at an early age and reared apart, 173 pairs of dizygotic twins reared apart, 129 monozygotic pairs reared together, and 168 dizygotic pairs reared together. At the time of data collection, 72% were over 50 years of age. Three LOC components were measured in a mailed questionnaire: sense of personal control or lack of control over the direction of one's own life (Life Direction), beliefs about how responsible people are for misfortunes in their lives (Responsibility), and beliefs concerning the role of luck in determining people's outcomes (Luck). Model-fitting results indicated that genetic influences were of importance for Life Direction and Responsibility, accounting for somewhat over 30% of the variance in each component, while environmental influences explained twin similarity for Luck.

Adoption↗