Twins Early Development Study
Encyclopedia
The Twins Early Development Study (TEDS) is an ongoing longitudinal twin study
, headed by principal investigator
and leading psychologist
Professor Robert Plomin
. The main goal of TEDS is to use behavioural genetic
methods to find out how nature (genes
) and nurture (environments) can explain why people differ with respect to their cognitive abilities, learning abilities and behaviours. Over 15,000 pairs of twins
originally signed up for the study and more than 13,000 pairs remain involved to the present day. This demonstrates the continued support of all twins and their families for more than a decade.
and Wales
between 1994 and 1996. When the twins were around 12 months old, a parent or guardian of the twins was asked to complete a first contact booklet, which listed a comprehensive range of background variables (e.g. information about ethnic origin, job status and educational qualifications). This background information has been updated through the course of the study and has enabled comparisons of the TEDS sample against UK population data and against participants lost to attrition
. These comparisons have led to the conclusion that, despite attrition, TEDS continues to be representative of the UK population, e.g. in terms of ethnicity, maternal education, and parental employment status. Zygosity
of twins was determined either using parental questionnaires or, in instances where questionnaire results were unclear, by DNA typing. Data has been collected longitudinally at ages 2, 3, 4, 7, 8, 9, 10, 12, 14 and 16
in order to investigate the genetic and environmental origins of common cognitive disabilities and abilities, learning disabilities and abilities (e.g. language, reading, mathematical abilities and disabilities) and behaviour problems (e.g. hyperactivity). Although the main focus remains on these topics, TEDS has also looked at other topics such as gender role
development, prosocial behaviour
, food choices, asthma
, and sources of heterogeneity and comorbidity
in psychopathology
. TEDS’ research also addresses the relationship between ability and disability, i.e. can disability be understood in terms of the extreme end of a continuum of normal variation in ability.
The incorporation of environmental measures (e.g. measures of home and school environment) in genetically sensitive designs allows TEDS to study the interplay between nature and nurture; such as exposure to certain environments for genetic reasons (gene-environment correlation
) and differential sensitivity to the environment based on people’s genetic make-up (gene-environment interaction
).
of learning abilities and disabilities, and important contributions to the literature on the heritability of IQ and school achievement. Novel findings from TEDS also include the discovery that social and non-social behaviours exhibited by children with autistic spectrum disorder (ASD) are largely influenced by different genes. With respect to molecular genetics, TEDS has pioneered a novel strategy called SNP Microarrays and Pooling (SNP-MaP), which is a cost-effective and powerful way of genotyping
DNA as it allows researchers to use one microarray instead of hundreds to genotype a group’s pooled DNA. It is hoped that it will eventually be possible to use the insights obtained from studies such as TEDS to help prevent or alleviate common learning disabilities such as dyslexia.
Twin study
Twin studies help disentangle the relative importance of environmental and genetic influences on individual traits and behaviors. Twin research is considered a key tool in behavioral genetics and related fields...
, headed by principal investigator
Principal investigator
A principal investigator is the lead scientist or engineer for a particular well-defined science project, such as a laboratory study or clinical trial....
and leading psychologist
Psychologist
Psychologist is a professional or academic title used by individuals who are either:* Clinical professionals who work with patients in a variety of therapeutic contexts .* Scientists conducting psychological research or teaching psychology in a college...
Professor Robert Plomin
Robert Plomin
Robert Plomin is an American psychologist best known for his work in twin studies and behavior genetics. Plomin has made two of the most important discoveries in that field. First, he has shown the importance of non-shared environment, a term that he coined to refer to the environmental reasons...
. The main goal of TEDS is to use behavioural genetic
Behavioural genetics
Quantitative human behavioural genetics is a specialisation in the biological field of behaviour genetics that studies the role of genetics in human behaviour employing quantitative-genetic methods. The field is an overlap of quantitative genetics and psychology...
methods to find out how nature (genes
Gênes
Gênes is the name of a département of the First French Empire in present Italy, named after the city of Genoa. It was formed in 1805, when Napoleon Bonaparte occupied the Republic of Genoa. Its capital was Genoa, and it was divided in the arrondissements of Genoa, Bobbio, Novi Ligure, Tortona and...
) and nurture (environments) can explain why people differ with respect to their cognitive abilities, learning abilities and behaviours. Over 15,000 pairs of twins
TWINS
Two Wide-Angle Imaging Neutral-Atom Spectrometers are a pair of NASA instruments aboard two United States National Reconnaissance Office satellites in Molniya orbits. TWINS was designed to provide stereo images of the Earth's ring current. The first instrument, TWINS-1, was launched aboard USA-184...
originally signed up for the study and more than 13,000 pairs remain involved to the present day. This demonstrates the continued support of all twins and their families for more than a decade.
The TEDS sample
Participants were identified from birth records of all twins born in EnglandEngland
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
and Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
between 1994 and 1996. When the twins were around 12 months old, a parent or guardian of the twins was asked to complete a first contact booklet, which listed a comprehensive range of background variables (e.g. information about ethnic origin, job status and educational qualifications). This background information has been updated through the course of the study and has enabled comparisons of the TEDS sample against UK population data and against participants lost to attrition
Attrition
Attrition may refer to:*Physical wear*Attrition warfare, the military strategy of wearing down the enemy by continual losses in personnel and material*Loss of personnel by Withdrawal...
. These comparisons have led to the conclusion that, despite attrition, TEDS continues to be representative of the UK population, e.g. in terms of ethnicity, maternal education, and parental employment status. Zygosity
Zygosity
Zygosity refers to the similarity of alleles for a trait in an organism. If both alleles are the same, the organism is homozygous for the trait. If both alleles are different, the organism is heterozygous for that trait...
of twins was determined either using parental questionnaires or, in instances where questionnaire results were unclear, by DNA typing. Data has been collected longitudinally at ages 2, 3, 4, 7, 8, 9, 10, 12, 14 and 16
Main research topics
TEDS was originally set up with funding from the Medical Research CouncilMedical Research Council (UK)
The Medical Research Council is a publicly-funded agency responsible for co-ordinating and funding medical research in the United Kingdom. It is one of seven Research Councils in the UK and is answerable to, although politically independent from, the Department for Business, Innovation and Skills...
in order to investigate the genetic and environmental origins of common cognitive disabilities and abilities, learning disabilities and abilities (e.g. language, reading, mathematical abilities and disabilities) and behaviour problems (e.g. hyperactivity). Although the main focus remains on these topics, TEDS has also looked at other topics such as gender role
Gender role
Gender roles refer to the set of social and behavioral norms that are considered to be socially appropriate for individuals of a specific sex in the context of a specific culture, which differ widely between cultures and over time...
development, prosocial behaviour
Prosocial behavior
Prosocial behavior, or "voluntary behavior intended to benefit another", consists of actions which "benefit other people or society as a whole," "such as helping, sharing, donating, co- operating, and volunteering." These actions may be motivated by empathy and by concern about the welfare and...
, food choices, asthma
Asthma
Asthma is the common chronic inflammatory disease of the airways characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm. Symptoms include wheezing, coughing, chest tightness, and shortness of breath...
, and sources of heterogeneity and comorbidity
Comorbidity
In medicine, comorbidity is either the presence of one or more disorders in addition to a primary disease or disorder, or the effect of such additional disorders or diseases.- In medicine :...
in psychopathology
Psychopathology
Psychopathology is the study of mental illness, mental distress, and abnormal/maladaptive behavior. The term is most commonly used within psychiatry where pathology refers to disease processes...
. TEDS’ research also addresses the relationship between ability and disability, i.e. can disability be understood in terms of the extreme end of a continuum of normal variation in ability.
The incorporation of environmental measures (e.g. measures of home and school environment) in genetically sensitive designs allows TEDS to study the interplay between nature and nurture; such as exposure to certain environments for genetic reasons (gene-environment correlation
Gene-environment correlation
Gene-environment correlation is said to occur when exposure to environmental conditions depends on an individual's genotype.-Definition:...
) and differential sensitivity to the environment based on people’s genetic make-up (gene-environment interaction
Gene-environment interaction
Gene–environment interaction is the phenotypic effect of interactions between genes and the environment....
).
Aims
TEDS follows three major aims.- Firstly, to use univariateUnivariateIn mathematics, univariate refers to an expression, equation, function or polynomial of only one variable. Objects of any of these types but involving more than one variable may be called multivariate...
quantitative geneticQuantitative geneticsQuantitative genetics is the study of continuous traits and their underlying mechanisms. It is effectively an extension of simple Mendelian inheritance in that the combined effects of one or more genes and the environments in which they are expressed give rise to continuous distributions of...
methods to explore the geneticIntroduction to geneticsGenetics is the study of genes, and tries to explain what they are and how they work. Genes are how living organisms inherit features from their ancestors; for example, children usually look like their parents because they have inherited their parents' genes...
and environmental origins of common learning and cognitive abilities and disabilities, i.e. to estimate the extent to which nature and nurture influence these abilities and disabilities.
- Secondly, to use multivariate and longitudinal quantitative genetic methods to go beyond the rudimentary nature-nurture question, i.e. to address how nature and nurture contribute to stability and change in these abilities and disabilities, and how they influence the relations between different abilities and disabilities. The latter includes within-domain comparisons, e.g. to what extent do different learning disabilities (such as reading and mathematics disability) share a common genetic or environmental origin? It also includes cross-domain comparisons, e.g. to what extent to do learning disabilities (e.g. reading disability) and behaviour problems (e.g. Attention-Deficit Hyperactivity DisorderAttention-deficit hyperactivity disorderAttention deficit hyperactivity disorder is a developmental disorder. It is primarily characterized by "the co-existence of attentional problems and hyperactivity, with each behavior occurring infrequently alone" and symptoms starting before seven years of age.ADHD is the most commonly studied and...
) share a common origin?
- Thirdly, to conduct molecular geneticMolecular geneticsMolecular genetics is the field of biology and genetics that studies the structure and function of genes at a molecular level. The field studies how the genes are transferred from generation to generation. Molecular genetics employs the methods of genetics and molecular biology...
research in order to identify specific genes involved in abilities and disabilities, e.g. using genetic associationGenetic associationGenetic association is the occurrence, more often than can be readily explained by chance, of two or more traits in a population of individuals, of which at least one trait is known to be genetic....
(such as genome-wide associationGenome-wide association studyIn genetic epidemiology, a genome-wide association study , also known as whole genome association study , is an examination of many common genetic variants in different individuals to see if any variant is associated with a trait...
) analyses to identify single nucleotide polymorphisms or Copy Number Variants associated with learning and cognitive (dis-)abilities. So far, DNA has been collected from more than 5,000 twin pairs in TEDS.
Major findings and contributions
Oliver & Plomin (2007) provide an overview of TEDS findings. TEDS has made major contributions to the Genetics and Education literature, such as the formulation of the Generalist Genes HypothesisGeneralist Genes Hypothesis
The Generalist Genes Hypothesis of learning abilities and disabilities was conceived by Professor Robert Plomin, one of the 100 most eminent psychologists of the 20th century...
of learning abilities and disabilities, and important contributions to the literature on the heritability of IQ and school achievement. Novel findings from TEDS also include the discovery that social and non-social behaviours exhibited by children with autistic spectrum disorder (ASD) are largely influenced by different genes. With respect to molecular genetics, TEDS has pioneered a novel strategy called SNP Microarrays and Pooling (SNP-MaP), which is a cost-effective and powerful way of genotyping
Genotyping
Genotyping is the process of determining differences in the genetic make-up of an individual by examining the individual's DNA sequence using biological assays and comparing it to another individual's sequence or a reference sequence. It reveals the alleles an individual has inherited from their...
DNA as it allows researchers to use one microarray instead of hundreds to genotype a group’s pooled DNA. It is hoped that it will eventually be possible to use the insights obtained from studies such as TEDS to help prevent or alleviate common learning disabilities such as dyslexia.