Continuity and change of genetic and environmental influences on reading and reading-related neurocognitive skills: A systematic review of longitudinal twin studies.

Learning to read is a dynamic and cumulative process beginning from birth and continuing through the school years. Empirical data showed a decrease of additive genetic (A) and shared environmental (C) components and an increase of non-shared environmental (E) components from preschool to middle school. However, our understanding of the aetiology of continuity and change of reading skills across this developmental period is limited. Following the PRISMA guidelines, we reviewed the results of behavioral genetic research on reading-related neurocognitive skills of 13 longitudinal twin and adoptive sibling studies spanning from preschool/kindergarten to middle/high school. Our findings suggested that continuity was mainly explained by A components throughout the study periods, and, although to a lesser extent and less consistently, by C components during the early years; change was explained by new E components throughout the years, and also by new A components in the early years. As we are interested in models relevant to traits with early onset during development, it is crucial to deepen the investigation of how developmental time can moderate the genetic and environmental variation.