The Genetic and Environmental Etiology of the Association between Vocabulary and Syntax in First Grade

ABSTRACT

This twin study examined the genetic and environmental etiology of vocabulary, syntax, and their association in first graders. French-speaking same-sex twins (n = 555) completed two vocabulary tests, and two scores of syntax were calculated from their spontaneous speech at 7 years of age. Multivariate latent factor genetic analyses showed that lexical skills were influenced mainly by the environment shared between the twins, whereas syntactic skills were influenced exclusively by genes and unique environment. Moreover, the moderate association between vocabulary and syntax was mostly due to common genetic factors. These novel findings may be attributable to the use of latent factors and the population studied. More research is needed to determine the specific factors involved in lexical and syntactic skills at this developmental period.

KEYWORDS:

• vocabulary
• syntax
• behavioural genetics
• school entry

Acknowledgments

We are grateful to the children who participated in this study. We also thank Marie-Josée Côte, Carol-Ann Thouin, Laura Thivierge, Sophie Blais-Michaud, and Myriam Gagnon-Couture for their contribution to transcription and codification.

Notes

¹ There are two types of genetic factors, additive (A) and dominant (D), but only additive factors were considered in the present study (see Note 2).

² Even though this pattern may suggest an ADE model, an ACE model was used to enable the comparison with the model used for vocabulary.

Additional information

Funding

This work was supported by the Canada Research Chairs; Canadian Institute for Advanced Research; Canadian Institutes of Health Research; Canadian Language and Literacy Research Network; Fonds de Recherche du Québec-Société et Culture; National Health Research and Development Program; and Social Sciences and Humanities Research Council of Canada.