J Speech Lang Hear Res

Purpose The goal of this study was to investigate the etiologic basis for the association between deficits in phonological memory (PM) and vocabulary in school-age children. Method Children with deficits in PM or vocabulary were identified within the International Longitudinal Twin Study (ILTS). The ILTS includes 1,045 twin pairs from the United States, Australia, and Scandinavia aged 5 to 8 years. We applied the DeFries-Fulker regression method to determine whether problems in PM and vocabulary tend to co-occur because of overlapping genes, overlapping environmental risk factors, or both. Results Among children with isolated PM deficits, we found significant bivariate heritability of PM and vocabulary weaknesses both within and across time. However, when probands were selected for a vocabulary deficit, there was no evidence for bivariate heritability. In this case, the PM-vocabulary relationship appeared to owe to common shared environmental experiences. Conclusions The findings are consistent with previous research on the heritability of specific language impairment and suggest that there are etiologic subgroups of children with poor vocabulary for different reasons, one more influenced by genes and another more influenced by environment.

23275423

PMC3615120

CDC Public Access