Colledge, E., Price, T. S., Spinath, F. M., Bishop, D. V. M., Dale, P. S., & Plomin, R. (im Druck). Genetic and environmental mediation of the relationship between language and nonverbal impairment in 4-year old twins. Journal of Speech, Language, and Hearing Research.


The current study of 4-year-old twins investigated the genetic and environmental origins of comorbidity between language impairment and nonverbal ability by testing the extent to which language impairment in one twin predicted nonverbal ability in the co-twin. Impairment of language ability was defined as scores below the 15th percentile on a general language scale derived from a battery of diverse language tests. 436 children were identified as language impaired, members of 160 MZ and 131 same-sex DZ twin pairs. Language-impaired probands also suffered significant impairments in nonverbal ability. DF analysis showed evidence for shared genetic influences on language impairment and nonverbal cognition in that language problems in one twin predicted poor nonverbal ability in the co-twin, much more so for MZ twins than for DZ twins. The current study also indicates that children with comorbid language and nonverbal problems (non-specific language impairment, NLI) represent a substantial portion of children with language impairment. It is thus important to concentrate future research efforts into development and outcomes of NLI as well as Specific Language Impairment (SLI).


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