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Studies of twin children provide a rich design for estimating genetic and environmental effects on children’s language acquisition. Studies have reported heritability for language phenotypes in the range of .24-.59, with increasing heritability with age. Twin studies document that heritability is likely to be higher in children with low levels of language ability. Methods vary across studies, with important differences in measurement that can influence outcomes and interpretations. Limitations include incomplete information about possible confounds with twinning effects early in development, use of sample-internal standard scores, limited speech and language phenotypes per study, and restricted age ranges. This presentation will summarize outcomes from two studies of population-ascertained twin children, Study 1 with children ages 4 and 6 years (N=1151) and Study 2 with 810 16-year-old twins. The studies investigated multiple speech and language phenotypes, including TNS and AGR markers. Key outcomes are residual twinning effects at 4 and 6 years and relatively high heritability for language, especially for TNS/AGR markers.
Funding source: R01DC005226, MR/M021475/1 and previously G0901245 U.K. Medical Research Council
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