Reading exposure: a (largely) environmental risk factor with environmentally-mediated effects on reading performance in the primary school years.
BACKGROUND
It is widely believed that there are reciprocal links between reading achievement and reading exposure: children who read more do better at reading, and reading achievement itself promotes reading. We tested the hypotheses that these links arise because children's genetically influenced reading performance is correlated with their leisure-time reading exposure, and reading exposure, in turn, may have an environmentally mediated effect on later reading performance.


METHODS
The sample consisted of 3039 twin pairs from the UK Twins Early Development Study (TEDS). Reading exposure was assessed at age 10 using the Author Recognition Test (ART). Reading performance was assessed at ages 7 and 12 using the Test of Word Reading Efficiency (TOWRE).


RESULTS
ART scores were moderately correlated with TOWRE scores at ages 7 and 12. Shared environmental variance in 7-year TOWRE performance accounted for most of the contribution made by 7-year TOWRE scores to the prediction of 10-year ART scores. Genetic influences on ART scores were modest, but this genetic variance almost completely reflected genetic variance in 7-year TOWRE scores. After controlling for genetic and environmental influences that overlapped between 7-year TOWRE and 10-year ART scores, there was evidence for a separate link between 10-year ART and 12-year TOWRE that was due to shared environmental influences.


CONCLUSIONS
Genetic influences on early reading achievement contribute to later propensities to seek out reading experiences that might, in turn, reciprocally influence reading achievement through shared environmental paths.
Harlaar
Nicole
N
MRC Social, Genetic, & Developmental Psychiatry Centre, Institute of Psychiatry, King's College London, UK. n.harlaar@iop.kcl.ac.uk
Dale
Philip S
PS
Plomin
Robert
R
D000124:Achievement; D000367:Age Factors; D002648:Child; D002657:Child Development; D004410:Dyslexia / Q000235:genetics; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D014644:Genetic Variation; D005838:Genotype; D006801:Humans; D007807:Language Tests / Q000706:statistics & numerical data; D008297:Male; D008957:Models, Genetic; D010641:Phenotype; D011214:Practice, Psychological; D011932:Reading; D021641:Recognition, Psychology; D012307:Risk Factors; D012931:Social Environment; D014427:Twins / Q000235:genetics*; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic