title: Genetic and environmental origins of verbal and performance components of cognitive delay in 2-year-olds.
abstract: The authors investigated the etiology of several measures of cognitive delay. Verbal (V) and performance (P) abilities were assessed in over 3,000 pairs of 2-year-old twins. Group-differences heritability for general delay (the lowest 5% of the V and P composite) was 35%. However, V and P delays considered independently showed large differences in group heritability (77% for V vs. 40% for P). Specific delays with comorbid cases eliminated showed an even greater difference in group heritability (78% vs. 22%, respectively). The small sample comorbid for both V and P delay also yielded high group heritability for both V (77%) and P (93%) scores. Shared environmental factors also differed in magnitude for V (20%) and P (41%) delays. Because the genetic and environmental origins of V and P delays in infancy differ, they are better considered separately rather than combined into a composite measure of general cognitive delay.
authors.affiliation: Social, Genetic and Developmental Psychiatry Research Centre, Institute of Psychiatry, London, United Kingdom. t.eley@iop.kcl.ac.uk
authors.forename: T C
authors.initials: TC
authors.lastname: Eley
authors.forename: D V
authors.initials: DV
authors.lastname: Bishop
authors.forename: P S
authors.initials: PS
authors.lastname: Dale
authors.forename: B
authors.initials: B
authors.lastname: Oliver
authors.forename: S A
authors.initials: SA
authors.lastname: Petrill
authors.forename: T S
authors.initials: TS
authors.lastname: Price
authors.forename: S
authors.initials: S
authors.lastname: Purcell
authors.forename: K J
authors.initials: KJ
authors.lastname: Saudino
authors.forename: E
authors.initials: E
authors.lastname: Simonoff
authors.forename: J
authors.initials: J
authors.lastname: Stevenson
authors.forename: R
authors.initials: R
authors.lastname: Plomin
mesh_terms: D002675:Child, Preschool; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D020022:Genetic Predisposition to Disease / Q000235:genetics; D006801:Humans; D007206:Individuality; D007360:Intelligence / Q000235:genetics; D007805:Language Development Disorders / Q000235:genetics* / Q000523:psychology; D008297:Male; D011596:Psychomotor Disorders / Q000235:genetics* / Q000523:psychology; D012307:Risk Factors; D012931:Social Environment; D014825:Vocabulary