title: Shared etiology of phonological memory and vocabulary deficits in school-age children.
abstract: OBJECTIVE
  The goal of this study was to investigate the etiologic basis for the association between deficits in phonological memory (PM) and vocabulary in school-age children.
  
  
  METHODS
  Children with deficits in PM or vocabulary were identified within the International Longitudinal Twin Study (ILTS; Samuelsson et al., 2005). The ILTS includes 1,045 twin pairs (between the ages of 5 and 8 years) from the United States, Australia, and Scandinavia. The authors applied the DeFries-Fulker ( DeFries & Fulker, 1985, 1988) regression method to determine whether problems in PM and vocabulary tend to co-occur because of overlapping genes, overlapping environmental risk factors, or both.
  
  
  RESULTS
  Among children with isolated PM deficits, the authors found significant bivariate heritability of PM and vocabulary weaknesses both within and across time. However, when probands were selected for a vocabulary deficit, there was no evidence for bivariate heritability. In this case, it appears that the PM-vocabulary relationship is caused by common shared environmental experiences.
  
  
  CONCLUSIONS
  The findings are consistent with previous research on the heritability of specific language impairment and suggest that there are etiologic subgroups of children with low vocabulary for different reasons, 1 being more influenced by genes and another being more influenced by environment.
authors.affiliation: University of Denver, CO, USA. robin.peterson@du.edu
authors.forename: Robin L
authors.initials: RL
authors.lastname: Peterson
authors.forename: Bruce F
authors.initials: BF
authors.lastname: Pennington
authors.forename: Stefan
authors.initials: S
authors.lastname: Samuelsson
authors.forename: Brian
authors.initials: B
authors.lastname: Byrne
authors.forename: Richard K
authors.initials: RK
authors.lastname: Olson
mesh_terms: D001184:Articulation Disorders / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics; D001315:Australia / Q000453:epidemiology; D002648:Child; D002675:Child, Preschool; D004777:Environment; D005260:Female; D006801:Humans; D007805:Language Development Disorders / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics; D008137:Longitudinal Studies; D008297:Male; D008568:Memory; D008569:Memory Disorders / Q000453:epidemiology / Q000209:etiology* / Q000235:genetics; D010641:Phenotype; D010700:Phonetics; D012042:Registries; D012307:Risk Factors; D012537:Scandinavian and Nordic Countries / Q000453:epidemiology; D014429:Twins, Dizygotic / Q000706:statistics & numerical data; D014430:Twins, Monozygotic / Q000706:statistics & numerical data; D014481:United States / Q000453:epidemiology; D014825:Vocabulary