Gene x Environment interactions in speech sound disorder predict language and preliteracy outcomes.

Few studies have investigated the role of gene x environment interactions (G x E) in speech, language, and literacy disorders. Currently, there are two theoretical models, the diathesis-stress model and the bioecological model, that make opposite predictions about the expected direction of G x E, because environmental risk factors may either strengthen or weaken the effect of genes on phenotypes. The purpose of the current study was to test for G x E at two speech sound disorder and reading disability linkage peaks using a sib-pair linkage design and continuous measures of socioeconomic status, home language/literacy environment, and number of ear infections. The interactions were tested using composite speech, language, and preliteracy phenotypes and previously identified linkage peaks on 6p22 and 15q21. Results showed five G x E at both the 6p22 and 15q21 locations across several phenotypes and environmental measures. Four of the five interactions were consistent with the bioecological model of G x E. Each of these four interactions involved environmental measures of the home language/literacy environment. The only interaction that was consistent with the diathesis-stress model was one involving the number of ear infections as the environmental risk variable. The direction of these interactions and possible interpretations are explored in the discussion.