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. 2012 May;42(5):1091-102.
doi: 10.1017/S0033291711002339. Epub 2011 Dec 2.

Lower birth weight indicates higher risk of autistic traits in discordant twin pairs

M Losh  1 , D Esserman, H Anckarsäter, P F Sullivan, P Lichtenstein
Affiliations

Lower birth weight indicates higher risk of autistic traits in discordant twin pairs

M Losh et al. Psychol Med. 2012 May.

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.

Method: 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.

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Conflict of interest statement

The authors have no conflicts of interest to declare.

Figures

Figure 1
Figure 1
Flow chart illustrating twin-pairs examined in analyses of birth weight and ASD. ASD defined as score of ≥4.5 on the ASD module of the A-TAC. *Note: Sex-discordant pairs were not included in analyses.
Figure 2
Figure 2
a: ASD symptoms and birth weight differences for discordant male twin-pairs. b: ASD symptoms and birth weight differences for discordant female twin-pairs.
Figure 2
Figure 2
a: ASD symptoms and birth weight differences for discordant male twin-pairs. b: ASD symptoms and birth weight differences for discordant female twin-pairs.
See this image and copyright information in PMC

References

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