Estimates Of Genetic Influences Research Articles

What Do People Know About the Heritability of Sleep?

Twin studies have provided data about the relative weight of genetic and environmental factors on sleep variables over the last few decades. However, heritability is a non-intuitive concept and it is often misunderstood even amongst the scientific community. This study aimed to analyze: (1) understanding of the meaning of heritability of insomnia; (2) the accuracy of estimations of heritability in the general population regarding three sleep traits (sleep duration, sleep quality and insomnia); (3) perceptions of the effectiveness of different treatments for insomnia depending on how the disorder is presented (i.e. having an environmental or genetic etiology) and whether the subject's estimate of genetic influence on sleep traits impacted beliefs about the effectiveness of different treatments. Participants (N = 3658) completed a survey which included: questions about general genetic knowledge; a specific question about the meaning of heritability; estimates of heritability of three different sleep traits; and the effectiveness of different treatments for insomnia depending on how the etiology of this condition was presented. Fewer than 25% of the participants selected the correct description of the heritability of insomnia. Almost half of the sample incorrectly believed that heritability refers to the chance of passing a disorder onto their children. We also found that participants provided different estimates for the effectiveness of different treatments depending on the presumed etiology of the disorder. Most people do not have accurate knowledge about the concept of heritability. People's assumptions about the etiology of a disorder may influence which treatments they consider most effective.

Challenge to the assumed rarity of heteropaternal superfecundation: findings from a case report

ABSTRACT Heteropaternal superfecundation (HP) is the fertilization, within the same cycle, of simultaneously released ova by sperm from separate males. The twin offspring resulting from HP are genetically equivalent to half-siblings, sharing an average of 25% of their genetic complement, by descent. The frequency of such twins is unknown and assumed to be rare, but is likely to be underestimated. Reasons for underestimation include inadequate detection, absence of confirmation, links between illegitimate births and dizygotic twinning, modern reproductive technologies and public unawareness of such pairs. A recently identified case of heteropaternal female twins is illustrative in this regard. HP twins pose significant implications for paternity suits, organ donation and other forensic inquiries. Recognizing the importance of this special class of non-identical twins is further emphasized, given that their inclusion in modest size twin samples might spuriously inflate estimates of genetic influence underlying measured traits.

The Impact of Variation in Twin Relatedness on Estimates of Heritability and Environmental Influences.

By taking advantage of the natural variation in genetic relatedness among identical (monozygotic: MZ) and fraternal (dizygotic: DZ) twins, twin studies are able to estimate genetic and environmental contributions to complex human behaviors. Recently concerns have been raised about the accuracy of twin studies in light of findings of genetic and epigenetic changes in twins. One of the concerns raised is that MZ twins are not 100% genetically and epigenetically similar because they show variations in their genomes and epigenomes leading to inaccurate estimates of heritability. This article presents findings from a simulation study that examined the degree of bias in estimates of heritability and environmentality when the genetic and epigenetic similarity of MZ twins differs from 1.00 and when the genetic and epigenetic similarity of DZ twins differs from 0.50. The findings suggest that in the standard biometric model when MZ or DZ twin similarity differs from 1.00 or 0.50, respectively, the variance that should be attributed to genetic influences is instead attributed to nonshared environmental influences, thus deflating the estimates of genetic influences and inflating the estimates of nonshared environmental influences. Although estimates of genetic and nonshared environmental influences from the standard biometric model were found to deviate from "true" values, the bias was usually smaller than 10% points indicating that the interpretations of findings from previous twin studies are mostly correct.

Changes in genetic risk for emotional eating across the menstrual cycle: a longitudinal study.

Previous studies have shown significant within-person changes in binge eating and emotional eating across the menstrual cycle, with substantial increases in both phenotypes during post-ovulation. Increases in both estradiol and progesterone levels appear to account for these changes in phenotypic risk, possibly via increases in genetic effects. However, to date, no study has examined changes in genetic risk for binge phenotypes (or any other phenotype) across the menstrual cycle. The goal of the present study was to examine within-person changes in genetic risk for emotional eating scores across the menstrual cycle. Participants were 230 female twin pairs (460 twins) from the Michigan State University Twin Registry who completed daily measures of emotional eating for 45 consecutive days. Menstrual cycle phase was coded based on dates of menstrual bleeding and daily ovarian hormone levels. Findings revealed important shifts in genetic and environmental influences, where estimates of genetic influences were two times higher in post- as compared with pre-ovulation. Surprisingly, pre-ovulation was marked by a predominance of environmental influences, including shared environmental effects which have not been previously detected for binge eating phenotypes in adulthood. Our study was the first to examine within-person shifts in genetic and environmental influences on a behavioral phenotype across the menstrual cycle. Results highlight a potentially critical role for these shifts in risk for emotional eating across the menstrual cycle and underscore the need for additional, large-scale studies to identify the genetic and environmental factors contributing to menstrual cycle effects.

Increasing phenotypic and genetic variations in hyperactivity/inattention problems from age 3 to 13 years: a cross-sectional twin study.

A twin design was used to examine the developmental nature of genetic, environmental, and phenotypic variations in hyperactivity and inattention problems (HIP). Mothers of 662 complete pairs of twins (273 monozygotic [MZ] pairs and 389 dizygotic [DZ] pairs) aged from 3 to 13 years (mean [SD] age = 8.3 [2.9] years) responded to the items of the HIP scale of the Strengths and Difficulties questionnaire via a telephone interview. Maximum likelihood MZ and DZ twin correlations in the total sample were 0.47 (95% CI: 0.37-0.55) and -0.01 (95% CI: -0.11-0.09). A standard univariate model incorporating age as a modifier was applied to the raw data. Results of model-fitting analyses showed that the phenotypic variation of HIP monotonically increased from age 3 to age 12 and that this increase was completely due to an increase in genetic variance, suggesting that it is genes that expand individual difference in ADHD symptoms with age during childhood. Child-specific environmental variance was constant during this age period. In terms of relative influences, total genetic factors increased from 33% (95% CI: 27-44%) at age 3 to 51% (95% CI: 28-71%) at age 13 and this increase was accompanied by a decrease in relative influences of child-specific environmental factors from 67% (95% CI: 56-73%) at age 3 to 49% (95% CI: 29-72%) at age 13. These estimates of genetic influences were somewhat lower than those found in most twin studies of ADHD symptoms. However, the increasing trend of genetic influences with age during childhood was consistent with the results of a recent meta-analysis of ADHD symptoms.

Genetic Influences on Childhood Competencies: A Twin Study

To estimate genetic, environmental, and rater contrast influences on parental reports of Activities, Social, School, and Total Competence scales of the Child Behavior Checklist (CBCL). Parents of 492 twin pairs aged 8-12 years completed CBCLs. Genetic, shared and unique environmental, and rater bias effects were estimated for the Activities, Social, School, and Total Competence scales. Data on boys and girls were analyzed separately. Moderate genetic influences were found only for the School scale (60%-76%), while shared environment accounted for most of the variance in Activities, Social, and Total Competence scales. Gender differences are reported. Similar to a prior twin study of CBCL problem syndromes, there was no evidence of rater bias. Estimates of genetic influence on these child competence domains were high for School Competence, while social competence and activity competence evidenced higher levels of shared environmental influences. Organization and wording of CBCL items may avoid rater biases in reporting. These findings have implications for interventions to improve school, social, and activities competence.

Sex differences in ethanol-related behaviors in genetically defined murine stocks.

Over the past 30 years, there have been a number of important developments in our understanding of the etiology and consequences of excessive drinking among humans. Probably one of the most important findings to date is that there are large individual differences among humans in appetite for alcohol and age of onset of problem drinking. We recognize this finding in at least two different alcoholic types, each with its own estimate of genetic influence. We have also come to realize that there are important differences between men and women, both in etiology of problem drinking and in the consequences of chronic alcohol use. In this chapter, the advantages and limitations of applying genetically defined animal models, primarily, selected lines and inbred strains of mice, are evaluated with examples from the literature.

A Twin Study of Inattentive, Aggressive, and Anxious/Depressed Behaviors

To estimate genetic, environmental, and rater contrast influences on parental report of Attention Problems (AP), Aggressive (Agg), and Anxious/Depressed (AxD) behaviors of 492 twin pairs assessed with the Child Behavior Checklist. A parent (92% mothers) of twins aged 8 to 12 years completed the Child Behavior Checklist. Genetic, shared and unique environmental, and rater bias effects were estimated for the AP, Agg, and AxD syndromes. Data on boys and girls were analyzed separately. Results were compared to prior research on related DSM disorders. Estimates of genetic influences on AP (60%-68%), Agg (70%-77%), and AxD (61%-65%) were high for both sexes, but lower for AP than prior findings using DSM attention-deficit hyperactivity disorder (ADHD). However, unlike equivalent analyses of DSM ADHD based on parental report, there was no evidence of rater bias. Estimates of genetic influence on these common child psychopathological domains were high. There was no evidence of rater contrast effects. These findings have implications for diagnosis, particularly when assessing families with multiple children.

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.

The generalizability of genetic estimates

Evidence for both the differential and generalizable nature of estimates of genetic influence has recently been found across distinct ethnic and national groups. Estimates of genetic influence on cognitive tasks calculated from Korean parent-offspring regressions significantly correlate with similar estimates from Japanese-American and European-American samples, and together they predict similarities between spouses in still other samples. Heritabilities calculated for personality in Australian twins significantly correlate with those calculated in British twins and, together with heritabilities for social attitudes calculated in Australian twins, they predict similarities between Canadian friends. Inbreeding depression scores calculated in Japan on the WISC subtests in the 1950s predict black-white difference scores on the WISC—R in the 1970s. These findings cannot be attributed to the confounding effects of measurement error for the relationships remain after controlling for reliability. The results suggest that estimates of genetic influence on various traits may be more robust across populations,languages, time periods and measurement specifics than has been considered to date.

Application of nonlinear factor analysis to genotype-environment interaction.

The intention of this paper is to show how the methods of nonlinear factor analysis as developed by McDonal (Br. J. Math. Stat. Psychol.20:205–215, 1967) can be used to study genotype-environment interaction. The method is applied to the interaction of genotype and within-family environmental influences. Simulated twin data are used to illustrate how this type of interaction may be detected and estimated. It is shown that estimates of genetic influences are not affected byG×E interaction.