Shared Reading at Age 1 Year and Later Vocabulary: A Gene–Environment Study

Objective: To assess the extent to which associations between shared reading at age 1 years and child vocabulary at age 3 years differ based on the presence of sensitizing alleles in the dopaminergic and serotonergic neurotransmitter systems. Study design: We conducted a secondary analysis of data from a national urban birth cohort using mother reports in conjunction with child assessments and salivary genetic data. Child vocabulary was assessed using the Peabody Picture Vocabulary Test. The primary exposure was mother-reported shared reading. We used data on gene variants that may affect the function of the dopaminergic and serotonergic systems. We examined associations between shared reading and Peabody Picture Vocabulary Test score using multiple linear regression. We then included interaction terms between shared reading and the presence of sensitizing alleles for each polymorphism to assess potential moderator effects adjusting for multiple comparisons. Results: Of the 1772 children included (56% black, 52% male), 31% of their mothers reported reading with their child daily. Daily shared reading was strongly associated with child Peabody Picture Vocabulary Test scores in unadjusted (B = 7.9; 95% CI, 4.3-11.4) and adjusted models (B = 5.3; 95% CI, 2.0-8.6). The association differed based on the presence of sensitizing alleles in the dopamine receptor 2 and serotonin transporter genes. Conclusions: Among urban children, shared reading at age 1 years was associated with greater vocabulary at age 3 years. Although children with sensitizing alleles on the dopamine receptor 2 and serotonin transporter genes were at greater risk when not read to, they fared as well as children without these alleles when shared reading occurred.