Posts tagged heritability
Articles and news from the latest research reports.
Why is educational achievement heritable?
New research, led by King’s College London finds that the high heritability of exam grades reflects many genetically influenced traits such as personality, behaviour problems, and self-efficacy and not just intelligence.
The study, published today in the Proceedings of the National Academy of Sciences (PNAS), looked at 13,306 twins at age 16 who were part of the Medical Research Council (MRC) funded UK Twins Early Development Study (TEDS). The twins were assessed on a range of cognitive and non-cognitive measures, and the researchers had access to their GCSE (General Certificate of Secondary Education) scores.
In total, 83 scales were condensed into nine domains: intelligence, self-efficacy (confidence in one’s own academic ability), personality, well-being, home environment, school environment, health, parent-reported behaviour problems and child reported behaviour problems.
Identical twins share 100% of their genes, and non-identical twins (just as any other siblings) share 50% of the genes that vary between people. Twin pairs share the same environment (family, schools, teachers etc). By comparing identical and non-identical twins, the researchers were able to estimate the relative contributions of genetic and environmental factors. So, if overall, identical twins are more similar on a particular trait than non-identical twins, the differences between the two groups are due to genetics, rather than environment.
Eva Krapohl, joint first author of the study, from the MRC Social, Genetic and Developmental Psychiatry (SGDP) Centre at the Institute of Psychiatry, Psychology & Neuroscience (IoPPN) at King’s, says: “Previous work has already established that educational achievement is heritable. In this study, we wanted to find out why that is. What our study shows is that the heritability of educational achievement is much more than just intelligence – it is the combination of many traits which are all heritable to different extents.
“It is important to point out that heritability does not mean that anything is set in stone. It simply means that children differ in how easy and enjoyable they find learning and that much of these differences are influenced by genetics.”
The researchers found that the heritability of GCSE scores was 62%. Individual traits were between 35% and 58% heritable, with intelligence being the most highly heritable. Together, the nine domains accounted for 75% of the heritability of GCSE scores.
Heritability is a population statistic which does not provide any information at an individual level. It describes the extent to which differences between children can be ascribed to DNA differences, on average, in a particular population at a particular time.
(Source: kcl.ac.uk)
Twin study suggests language delay due more to nature than nurture
A study of 473 sets of twins followed since birth found that compared with single-born children, 47 percent of 24-month-old identical twins had language delay compared with 31 percent of nonidentical twins. Overall, twins had twice the rate of late language emergence of single-born children. None of the children had disabilities affecting language acquisition.
The results of the study were published in the June 2014 Journal of Speech, Language, and Hearing Research.
University of Kansas Distinguished Professor Mabel Rice, lead author, said that all of the language traits analyzed in the study—vocabulary, combining words and grammar—were significantly heritable with genes accounting for about 43 percent of the overall twins’ deficit.
The “twinning effect” — a lower level of language performance for twins than single-born children — was expected to be comparable for both kinds of twins, but was greater for identical twins, said Rice, strengthening the case for the heritability of language development.
“This finding disputes hypotheses that attribute delays in early language acquisition of twins to mothers whose attention is reduced due to the demands of caring for two toddlers,” Rice said. “This should reassure busy parents who worry about giving sufficient individual attention to each child.”
However, said Rice, prematurity and birth complications, more common in identical twins, could also affect their higher rates of language delay. A study of pregnancy and birth risks for late talking in twins is currently under way by the study authors.
Further, the study will continue at least until 2017 to continue to follow the twins through preschool and school years up to adolescence to answer the question of whether late-talking twins do catch up to their peers.
“Twin studies provide unique opportunities to study inherited and environmental contributions to language acquisition,” Rice said. “The outcomes inform our understanding of how these influences contribute to language acquisition in single-born children as well.”
Late language emergence means that a child’s language is below age and gender expectations in the number of words they speak and combining two or more words into sentences. In this study, 71 percent of 2-year-old twins were not combining words compared with 17 percent of single-born children.
While previous behavioral genetics studies of toddlers have largely focused on vocabulary, the researchers introduced an innovative measure of early grammatical ability on the correct use of the past tense and the “to be” and “to do” verbs. The measure was inspired by the Rice/Wexler Test of Early Grammar Impairment, developed in 2001 by Rice and Kenneth Wexler, Massachusetts Institute of Technology professor. It was the first test to detect the subtle but common language disorder, specific language impairment.
Rice’s collaborators in the international longitudinal project that began in 2002 are Professors Cate Taylor and Stephen Zubrick from the Telethon Kids Institute in Perth, Western Australia, and Professor Shelley Smith at the University of Nebraska Medical Center.
The study population is located in the vicinity of Perth, Western Australia, because it is demographically identical to Kansas City and several other U.S. Midwestern states. But in Australian health records are available, and the Western Australia Twin Registry is a unique resource for researchers since it is a record of all multiple births, Rice said.
The research group has followed the development of 1,000 sets of Western Australian twins from their first words. In 2012, the group was granted $2.8 million by the National Institute for Deafness and Other Communication Disorders for a fourth five-year-cycle that will enable researchers to continue to monitor the twins as they develop through adolescence. In addition to formal language tests, researchers have collected genetic and environmental data as well as assessments with the twins’ siblings.
(Source: news.ku.edu)
Chimp Intelligence “Runs In Families,” Environment Less Important
A chimpanzee’s intelligence is largely determined by its genes, while environmental factors may be less important than scientists previously thought, according to a Georgia State University research study.
The study found that some, but not all, cognitive, or mental, abilities, in chimpanzees depend significantly on the genes they inherit. The findings are reported in the latest issue of Current Biology.
“Intelligence runs in families,” said Dr. William Hopkins, professor in the Center for Behavioral Neuroscience at Georgia State and research scientist in the Yerkes National Primate Research Center at Emory University. “The suggestion here is that genes play a really important role in their performance on tasks while non-genetic factors didn’t seem to explain a lot. So that’s new.”
The role of genes in human intelligence or IQ has been studied for years, but Hopkins’ study is among the first to address heritability in cognitive abilities in nonhuman primates. Studies have shown that human intelligence is inherited through genes, but social and environmental factors, such as formal education and socioeconomic status, also play a role and are somewhat confounded with genetic factors. Chimpanzees, which are highly intelligent and genetically similar to humans, do not have these additional socio-cultural influences.
“Chimps offer a really simple way of thinking about how genes might influence intelligence without, in essence, the baggage of these other mechanisms that are confounded with genes in research on human intelligence,” Hopkins said.
The study involved 99 chimpanzees, ranging in age from 9 to 54, who completed 13 cognitive tasks designed to test a variety of abilities. Hopkins used quantitative genetics analysis to link the degree of relatedness between the chimpanzees to their similarities or differences in performance on the various cognitive measures to determine whether cognitive performance is inherited in chimpanzees.
Genes were found to play a role in overall cognitive abilities, as well as the performance on tasks in several categories.
Traditionally, researchers studying animal intelligence or animal learning have shared the view that environment and how previous behavior is reinforced affect how animals perform on a particular task.
“In our case, at least, it suggests that purely environmental explanations don’t really seem to tell the whole story,” Hopkins said. “Genes matter as well.”
Hopkins also studied the structure of chimpanzee intelligence to determine whether there were any similarities to the structure of human intelligence.
“We wanted to see if we gave a sample of chimpanzees a large array of tasks,” he said, “would we find essentially some organization in their abilities that made sense. The bottom line is that chimp intelligence looks somewhat like the structure of human intelligence.”
In the future, Hopkins wants to continue the study with an expanded sample size. He would also like to pursue studies to determine which genes are involved in intelligence and various cognitive abilities as well as how genes are linked to variation in the organization of the brain.
Hopkins also would like to determine which genes changed in human evolution that allowed humans to have such advanced intelligence.
(Image: Anup Shah / Nature Picture Library)
Environmental factors as important as genes in understanding autism
Environmental factors are more important than previously thought in understanding the causes of autism, and equally as important as genes, according to the largest study to date to look at how autism runs in families.
The study also shows that children with a brother or sister with autism are 10 times more likely to develop autism; 3 times if they have a half-brother or sister; and 2 if they have a cousin with autism, providing much needed information for parents and clinicians for assessing individual risk.
The study, which looked at over 2 million people, was led by researchers at King’s College London, Karolinska Institutet in Sweden and Mount Sinai in the US, and is published in JAMA today.
Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder defined by impairments in social interaction and communication and the presence of restrictive and repetitive behaviours. The exact causes are unknown but evidence has shown it is likely to include a range of genetic and environmental risk factors.
Using Swedish national health registers, the researchers analysed anonymous data from all 2 million children born in Sweden in between 1982 and 2006, 14,516 of which had a diagnosis of ASD. The researchers analysed pairs of family members: identical and non-identical twins, siblings, maternal and paternal half-siblings and cousins.
The study involved two separate measures of autism risk – heritability, which is the proportion of risk in the population that can be attributed to genetic factors; and Relative Recurrent Risk which measures individual risk for people who have a relative with autism.
Most previous studies have suggested that heritability of autism may be as high as 80-90%, but one study has hinted at a lower estimate. The new study is the largest and most comprehensive to date and estimates heritability of autism to be 50%, with the other 50% explained by non-heritable or environmental factors.
Environmental factors are split into ‘shared environments’ which are shared between family members (such as family socio-economic status), and ‘non-shared environments’ which are unique to the individual (such as birth complications or maternal infections or medication during the pre and perinatal period). In this study, factors which are unique to the individual, or ‘non-shared environments’ were the major source of environmental risk.
Professor Avi Reichenberg, author of the study from Mount Sinai Seaver Center for Autism Research, who led the study whilst at King’s College London, says: “Heritability is a population measure, so whilst it does not tell us much about risk at an individual level, it does tell us where to look for causes. We were surprised by our findings as we did not expect the importance of environmental factors in autism to be so strong. Recent research efforts have tended to focus on genes, but it’s now clear that we need much more research to focus on identifying what these environmental factors are. In the same way that there are multiple genetic factors to consider, there will likely be many different environmental factors contributing to the development of autism.”
In the other part of the study, the researchers looked at individual risk. In the general population, autism affects approximately 1 in 100 children. The researchers found that children with a brother or sister with autism were 10.3 times more likely to develop autism; 3.3-2.9 times if they had a half-brother or sister with autism; and 2.0 times if they had a cousin with autism. There were no differences in relative risk between genders. This is the first study to provide such a comprehensive and far reaching analysis of individual risk extended as far as cousins.
Dr Sven Sandin, author of the study from King’s College London and Karolinska, says: “Our study was prompted by a very basic question which parents often ask: ‘if I have a child with autism, what is the risk my next child will too?’ Our study shows that at an individual level, the risk of autism increases according to how close you are genetically to other relatives with autism. We can now provide accurate information about autism risk which can comfort and guide parents and clinicians in their decisions.”
(Source: eurekalert.org)