Mathematics, reading and IQ: A multivariate genetic analysis in 7-year-old twins

Mathematics performance in the early school years has recently been shown to be highly heritable as assessed by UK teachers following National Curriculum criteria. To what extent does this genetic influence on mathematics overlap with genetic influence on reading and on general cognitive ability (g or IQ)? For 2825 pairs of 7-year-old same-sex twins, we used teacher assessments of mathematics performance, teacher assessments of reading performance and the Test of Word Reading Efficiency (administered by telephone), and a telephone-administered cognitive battery (adapted form Wechsler Intelligence Scale for Children) to assess g. Strong correlations were found between reading and mathematics (0.70) and moderate correlations between mathematics and g (0.43) and between reading and g (0.47). Multivariate genetic analysis indicated substantial genetic overlap between mathematics, reading and g—genetic correlations ranged between 0.62 and 0.76. Nonetheless, fitting a trivariate Cholesky decomposition model to the data revealed the existence of both common
and independent genetic influences for mathematics. That is, significant mathematics-specific genetic variance was found, as well as significant genetic variance specific to mathematics and reading but independent of g, and significant genetic variance in mathematics in common with reading and g. Shared and nonshared environmental
influences only contributed modestly to the specific and common variance for all measures. We conclude that the same genes largely affect mathematics, reading, and g, although some specific genetic and, to a lesser extent environmental influences, also exist.