In a forthcoming report in Behavioral Genetics, Professor M. van Leeuwen of VU University (Amsterdam, NL) and colleagues reported that the vast majority of variation in children’s reading performance is heritable, with most of the variance in reading attributable to IQ and memory. The researchers studied twins and siblings (only some of whom had reading disabilities), and they measured children’s reading rate, how many times they could correctly tap blocks in a sequence that had just been displayed, the number times the children could correctly recall the location of a part of a visual display (a catepillar in different holes in an apple), repetition of sequences of digits, and IQ.
Before folks begin using this study to argue that there is a simple causal relationship between IQ and reading, please remember three things: (a) this research also implicates memory as an explanatory factor; (b) there are likely other factors that affect IQ, memory, and reading; and (c) even if lots of variance is explained by such factors as IQ and memory, the remaining variance is sufficient to allow fairly substantial instructional effects.
This study investigates the genetic relationship among reading performance, IQ, verbal and visuospatial working memory (WM) and short-term memory (STM) in a sample of 112, 9-year-old twin pairs and their older siblings. The relationship between reading performance and the other traits was explained by a common genetic factor for reading performance, IQ, WM and STM and a genetic factor that only influenced reading performance and verbal memory. Genetic variation explained 83% of the variation in reading performance; most of this genetic variance was explained by variation in IQ and memory performance. We hypothesize, based on these results, that children with reading problems possibly can be divided into three groups: (1) children low in IQ and with reading problems; (2) children with average IQ but a STM deficit and with reading problems; (3) children with low IQ and STM deficits; this group may experience more reading problems than the other two.
van Leeuwen, M. van den Berg, S. M., Peper, J. S., Hulshoff Pol, H. E., & Boomsma, D. I. (2009). Genetic covariance structure of reading, intelligence and memory in children. Behavioral Genetics, [forthcoming].
Link to the PubMed abstract I’ve reproduced here.