The genetic/environmental transmissions and innovations across reading from ages 5 to 15 years

The genetic/environmental transmissions and innovations across reading from ages 5 to 15 years

First Author: Ginette Dionne -- Laval University
Additional authors/chairs: 
Sara Mascheretti; Jeffrey Henry; Philippe Robaey; Mara Brendgen; Frank Vitaro; Michel Boivin; Cecilia Marino
Keywords: Behavioral Genetic, Reading Ability, Longitudinal, Individual Differences
Abstract / Summary: 

Purpose: Few studies have looked at how the genetic/environmental etiology of reading skills unfolds throughout the pre-school and school years. This study examines the additive genetic and environmental transmissions and innovations across reading skills at 8 time-points from ages 5 to 15 years.

Method: We used a Cholesky decomposition approach on data from 960 twins from the Québec Newborn Twin Study. Measures included letter knowledge at age 5, reading skills at 6, 7 and 8, teacher reports of reading achievement at 9, 10 and 12, and reading ability at 15.

Results: Correlations across ages ranged from .19-.50 before age 8, and increased thereafter (.36-.76). Genetic influences were moderate up to age 8 (.35-.41) and increased from age 9 onward (.61-.71). Genetic transmission from age 5 accounted for 25% to 60% of the heritability of all subsequent reading skills. Some genetic innovation at 8 also transmitted to subsequent reading skills. Other genetic innovations up to age 9 and shared environment innovations up to age 8 were mainly time-specific, as were modest unique environment influences (.18-.36).

Conclusions: Reading skills are increasingly stable and heritable from ages 5-15, with an etiological shift occurring by 8-9 years. Additive genetic influences mainly present at onset account for their stability. These findings are consistent with recent evidence showing that reading-susceptibility genes affect early brain development, neuronal migration, neurite outgrowth, cortical morphogenesis and ciliary structure/function. New studies must gain momentum to understand the effects of reading-susceptibility genes upon both the genetic stability and the time-specific innovations.