We studied the influence of genetic factors on individual differences in morningness-eveningness in a sample of Dutch twin families. Data were collected from adolescent twins (mean age 17.8 yr) and their parents (mean age of fathers 48.0 yr and of mothers 46.0 yr) and a sample of older twins (mean age 46.5 yr). Scores on morningness-eveningness were rated on a 5-point scale. Parents were more morning oriented than their children, and women were more morning oriented than men. With a twin-family study, separation of genetic and environmental influences on variation in morningness-eveningness is possible. Including parents and older twins in the study makes it possible to explore generation differences in these effects. The correlation between monozygotic twins was more than twice the correlation between dizygotic twins. This indicates that genetic effects may not operate in an additive manner. Therefore, a model that included genetic dominance was explored. Biometrical model fitting showed no sex differences for the magnitude of genetic and environmental factors. The total heritability--the sum of additive and nonadditive genetic influences--for morningness-eveningness was 44% for the younger generation and 47% for the older generation. However, the genetic correlation between the generations turned out to be lower than 0.5, suggesting that different genes for morningness-eveningness are expressed in both generations.
Background: In this study several aspects of attention were studied in 237 nearly 6-year-old twin pairs. Specifically, the ability to sustain attention and inhibition were investigated using a computerized test battery (Amsterdam Neuropsychological Tasks). Furthermore, the Teacher's Report Form (TRF) was filled out by the teacher of the child and the attention subscale of this questionnaire was analyzed. Methods: The variance in performance on the different tasks of the test battery and the score on the attention scale of the TRF were decomposed into a contribution of the additive effects of many genes (A), environmental effects that are shared by twins (C) and unique environmental influences not shared by twins (E) by using data from MZ and DZ twins. Results: The genetic model fitting results showed an effect of A and E for the attention scale of the TRF, and for some of the inhibition and sustained attention measures. For most of the attention variables, however, it was not possible to decide between a model with A and E or a model with C and E. Time-on-task effects on reaction time or number of errors and the delay after making an error did not show familial resemblances. A remarkable finding was that the heritability of the attention scale of the TRF was found to be higher than the heritability of indices that can be considered to be more direct measures of attention, such as mean tempo in the sustained attention task and response speed in the Go-NoGo task. Conclusion: In preschoolers, familial resemblances on sustained attention and inhibition were observed.
In this study aspects of selective attention and working memory were tested in a large sample of nearly 6-year old monozygotic and dizygotic twin pairs, using a computerized test battery (Amsterdam Neuropsychological tasks). In the selective attention task the presence of a foil signal (target signal at an irrelevant location) resulted in more false alarms than a non-target signal. In the working memory task an increase in memory load lead to an increase in response times and errors. We analyzed variations in absolute performance parameters (overall speed and accuracy) and relative performance parameters (increase in errors and/or reaction time). The results showed clear familial resemblances on performance. It proved difficult to ascribe these effects to shared genes or to shared environment. An exception was memory search rate, which was clearly heritable.KEY WORDS: Attention-deficit hyperactivity disorder; endophenotypes; selective attention; twin study; working memory.In order to study the genetics of childhood psychopathologies such as ADHD it is of great importance to identify endophenotypes that predict the liability of the pathology of interest. The advantage of an endophenotypic approach to study complex disorders (or complex traits, such as IQ) is that it allows the identification of genes that by themselves make only a small contribution to the trait under study. A minimal requirement for suitable endophenotypes is that they yield continuously quantifiable measures; another requirement is that endophenotypes are anchored in neuroscience (e.g., Castellanos andTannock, 2002, andBoomsma, 2001). Indeed, researchers of psychopathologies often make use of neurocognitive tasks that are known to activate particular brain systems, and that yield quantitative performance measures, usually reaction times and percentage of errors. For example, Bush et al., (1999), using a counting Stroop task, found that children with ADHD showed underactivation in the anterior cingulate cognitive division (ACcd), and a concurrent increase in distractor interference, relative to controls. Stroop performance may thus qualify as a suitable (cognitive) endophenotype, indicative of ADHD. However, the search for endophenotypes should also be guided by the fact that many psychopathologies are highly heritable, and a recent line of inquiry has started to focus on the heritabilities of the endophenotypes themselves.Twin, adoption and family studies have shown that many psychopathologies are highly heritable (for review, see Acosta et al., 2004). For example, the heritability of ADHD is estimated to be around between 50% and 90% (e.g., Thapar et al., 1999). In a similar vein, the heritability of attention problems as
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.