Nature Neuroscience
1, 324 - 328 (1998)
doi:10.1038/1142
Genetic influence on language delay in two-year-old childrenPhilip Dale1, Emily Simonoff2, Dorothy Bishop3, Thalia Eley2, Bonny Oliver2, Thomas Price2, Shaun Purcell2, Jim Stevenson4
& Robert Plomin21
Department of Psychology, University of Washington
, Seattle, Washington 98195, USA
2
Social, Genetic and Developmental Psychiatry Research
Centre, Institute of Psychiatry, London SE5 8AF,
UK
3
MRC Cognition and Brain Sciences Unit (formerly Applied
Psychology Unit), Cambridge, CB2 2EF, UK
4
Centre for Research into Psychological Development,
University of Southampton, Southampton, SO17 1BJ,
UK
Correspondence should be addressed to Robert Plomin r.plomin@iop.bpmf.ac.ukPrevious work suggests that most clinically significant language difficulties
in children do not result from acquired brain lesions or adverse environmental
experiences but from genetic factors that presumably influence early brain
development. We conducted the first twin study of language delay to evaluate
whether genetic and environmental factors at the lower extreme of delayed
language are different from those operating in the normal range. Vocabulary
at age two was assessed for more than 3000 pairs of twins. Group differences
heritability for the lowest 5% of subjects was estimated as 73% in model-fitting
analyses, significantly greater than the individual differences heritability
for the entire sample (25%). This supports the view of early language delay
as a distinct disorder. Shared environment was only a quarter as important
for the language-delayed sample (18%) as for the entire sample (69%).
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