Common variation near ROBO2 is associated with expressive vocabulary in infancy

Twin studies suggest that expressive vocabulary at similar to 24 months is modestly heritable. However, the genes influencing this early linguistic phenotype are unknown. Here we conduct a genome-wide screen and follow-up study of expressive vocabulary in toddlers of European descent from up to four studies of the EArly Genetics and Lifecourse Epidemiology consortium, analysing an early (15-18 months, 'one-word stage', N-Total = 8,889) and a later (24-30 months, 'two-word stage', N-Total = 10,819) phase of language acquisition. For the early phase, one single-nucleotide polymorphism (rs7642482) at 3p12.3 near ROBO2, encoding a conserved axon-binding receptor, reaches the genome-wide significance level (P = 1.3 x 10(-8)) in the combined sample. This association links language-related common genetic variation in the general population to a potential autism susceptibility locus and a linkage region for dyslexia, speech-sound disorder and reading. The contribution of common genetic influences is, although modest, supported by genome-wide complex trait analysis (meta-GCTA h(5-18-months)(2) = 0.13, meta-GCTA h(24-30-months)(2) = 0.14) and in concordance with additional twin analysis (5,733 pairs of European descent, h(24-months)(2) = 0.20).