Identical Genes, Unique Environments: A Qualitative Exploration of Persistent Monozygotic-Twin Discordance in Literacy and Numeracy

Sally A Larsen,William L Coventry,Annette Stevenson,Brian Byrne,Connie S Ho,Callie W Little,Richard K Olson

doi:10.3389/feduc.2019.00021

Sally A Larsen, William L Coventry + Show 5 more

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https://doi.org/10.3389/feduc.2019.00021

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Abstract

This study aimed to explore unique environmental factors impacting differential academic trajectories among Australian school students. Monozygotic (MZ) twin pairs who were consistently discordant in results of nationwide standardized tests of reading, numeracy or writing between Grades 3 and 9 were identified. MZ twins control for genes, gender, age and aspects of the home and school environment shared by twins. Thus any difference between MZ twins in academic outcomes can be attributed to the unique environment experienced by each twin. From 551 MZ twin pairs with three or four sets of test results, we identified 55 pairs who were substantially and consistently discordant in reading, numeracy or writing between Grades 3 and 9. Parents were contacted for interview, resulting in 40 semi-structured interviews. Qualitative data analysis revealed three major themes, interpreted by parents as possible contributors to persistent academic discordance: biological mechanisms, school-based factors and personal factors. We discuss implications for educational practice, policy and research.

Highlights

Twin studies of literacy and numeracy development among school students have shown that genes play a significant role in the emergence of individual differences, with estimates of heritability ranging from around 40% to around 75% (Haworth et al, 2007; Oliver et al, 2007; Asbury and Plomin, 2014; Grasby et al, 2016; Little et al, 2017)
Along with the longitudinal approach that we employ, a novel feature of the current study is an exploration of biomedical conditions that might impact upon academic achievement
Biomedical explanations of MZ twin discordance in academic achievement emerged as a key theme from the parent interviews

Summary

Introduction

Twin studies of literacy and numeracy development among school students have shown that genes play a significant role in the emergence of individual differences, with estimates of heritability ranging from around 40% to around 75% (Haworth et al, 2007; Oliver et al, 2007; Asbury and Plomin, 2014; Grasby et al, 2016; Little et al, 2017). The same studies have shown that factors affecting individual twins differently within pairs (usually termed “unique environment”) account for most of the variance not explained by genes. Even in studies where potential unique environment factors have been measured, they typically explain only a small portion of variance (Turkheimer and Waldron, 2000; Plomin et al, 2016). This conundrum has been termed the “missing environment” problem (Asbury et al, 2016), analogous to the missing heritability problem (Manolio et al, 2009). Biomedical conditions that could contribute to persistent twin discordance in academic domains might include birth complications, injuries, sensory difficulties, or illnesses affecting only one twin

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