title: Relative influence of genetics and shared environment on child mental health symptoms depends on comorbidity.
abstract: BACKGROUND
  Comorbidity among childhood mental health symptoms is common in clinical and community samples and should be accounted for when investigating etiology. We therefore aimed to uncover latent classes of mental health symptoms in middle childhood in a community sample, and to determine the latent genetic and environmental influences on those classes.
  
  
  METHODS
  The sample comprised representative cohorts of twins. A questionnaire-based assessment of mental health symptoms was used in latent class analyses. Data on 3223 twins (1578 boys and 1645 girls) with a mean age of 7.5 years were analyzed. The sample was predominantly non-Hispanic Caucasian (92.1%).
  
  
  RESULTS
  Latent class models delineated groups of children according to symptom profiles--not necessarily clinical groups but groups representing the general population, most with scores in the normative range. The best-fitting models suggested 9 classes for both girls and boys. Eight of the classes were very similar across sexes; these classes ranged from a "Low Symptom" class to a "Moderately Internalizing & Severely Externalizing" class. In addition, a "Moderately Anxious" class was identified for girls but not boys, and a "Severely Impulsive & Inattentive" class was identified for boys but not girls. Sex-combined analyses implicated moderate genetic influences for all classes. Shared environmental influences were moderate for the "Low Symptom" and "Moderately Internalizing & Severely Externalizing" classes, and small to zero for other classes.
  
  
  CONCLUSIONS
  We conclude that symptom classes are largely similar across sexes in middle childhood. Heritability was moderate for all classes, but shared environment played a greater role for classes in which no one type of symptom predominated.
authors: Department of Psychology and Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Matthew K
authors: MK
authors: Vendlinski
authors: Department of Psychology and Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Kristin N
authors: KN
authors: Javaras
authors: Department of Psychology and Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Carol A
authors: CA
authors: Van Hulle
authors: Department of Psychology, Arizona State University, Tempe, Arizona, United States of America.
authors: Kathryn
authors: K
authors: Lemery-Chalfant
authors: Department of Psychology, University of Oregon, Eugene, Oregon, United States of America.
authors: Rose
authors: R
authors: Maier
authors: Department of Psychology and Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: Richard J
authors: RJ
authors: Davidson
authors: Department of Psychology and Waisman Center, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
authors: H Hill
authors: HH
authors: Goldsmith
mesh_terms: D002648:Child; D015897:Comorbidity; D005260:Female; D006801:Humans; D008297:Male; D001523:Mental Disorders / Q000150:complications / Q000235:genetics* / Q000503:physiopathology