title: Lower birth weight indicates higher risk of autistic traits in discordant twin pairs.
abstract: BACKGROUND
  Autism spectrum disorder (ASD) is a neurodevelopmental disorder of complex etiology. Although strong evidence supports the causal role of genetic factors, environmental risk factors have also been implicated. This study used a co-twin-control design to investigate low birth weight as a risk factor for ASD.
  
  
  METHODS
  We studied a population-based sample of 3715 same-sex twin pairs participating in the Child and Adolescent Twin Study of Sweden (CATSS). ASD was assessed using a structured parent interview for screening of ASD and related developmental disorders, based on DSM-IV criteria. Birth weight was obtained from medical birth records maintained by the Swedish Medical Birth Registry.
  
  
  RESULTS
  Twins lower in birth weight in ASD-discordant twin pairs (n=34) were more than three times more likely to meet criteria for ASD than heavier twins [odds ratio (OR) 3.25]. Analyses of birth weight as a continuous risk factor showed a 13% reduction in risk of ASD for every 100 g increase in birth weight (n=78). Analysis of the effect of birth weight on ASD symptoms in the entire population (most of whom did not have ASD) showed a modest association. That is, for every 100 g increase in birth weight, a 2% decrease in severity of ASD indexed by scores on the Autism - Tics, attention-deficit hyperactivity disorder (AD/HD), and other Comorbidities (A-TAC) inventory would be expected in the sample as a whole.
  
  
  CONCLUSIONS
  The data were consistent with the hypothesis that low birth weight confers risk to ASD. Thus, although genetic effects are of major importance, a non-genetic influence associated with birth weight may contribute to the development of ASD.
authors: Roxelyn and Richard Pepper Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL 60208, USA. m-losh@northwestern.edu
authors: M
authors: M
authors: Losh
authors: D
authors: D
authors: Esserman
authors: H
authors: H
authors: Anckarsäter
authors: P F
authors: PF
authors: Sullivan
authors: P
authors: P
authors: Lichtenstein
mesh_terms: D002648:Child; D002659:Child Development Disorders, Pervasive / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D015331:Cohort Studies; D004200:Diseases in Twins / Q000175:diagnosis / Q000453:epidemiology* / Q000523:psychology; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007230:Infant, Low Birth Weight / Q000523:psychology*; D007231:Infant, Newborn; D007406:Interview, Psychological; D008297:Male; D016017:Odds Ratio; D012042:Registries; D012307:Risk Factors; D012720:Severity of Illness Index; D013548:Sweden / Q000453:epidemiology; D014427:Twins