Environmental factors fail to explain rise in autism prevalence

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Disclosures: One study author reports grants from the Swedish Research Council while conducting the study, and another study author reports grants and personal fees from Shire/Takeda and personal fees from Evolan in outside of the submitted work. The other authors report no relevant financial information.


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Environmental factors linked to autism spectrum disorders have not increased in importance over time and are therefore unlikely to explain the increase in the prevalence of ASD, according to the results of a dual-design study published in JAMA Psychiatry.

“Twin methods provide a tool for testing [the environmental] hypothesis because they can compare the magnitude of genetic and environmental contributions with a trait across different groups, such as individuals born in different time periods,” Mark J. Taylor, PhD, from the Department of Medical Epidemiology and Biostatistics at the Karolinska Institutet in Stockholm, and colleagues wrote. “If changes in the environment over time explain the changing prevalence of a trait, then one hypothesis is that the environmental variance should increase over time. If the underlying genetic variance showed little or no of change, then the heritability of a given trait would also be expected to decrease.

Taylor and colleagues sought to assess whether this hypothesis holds true for ASDs by studying whether the relative importance of environmental and genetic associations with ASDs and autistic traits changed over a 16- and 26-year period.

The researchers analyzed data from two Swedish nationwide cohorts of twins – the Swedish Twin Registry (STR), which included participants born between January 1982 and December 2008, and the Child and Adolescent Twins Study in Sweden (CATSS), which included participants born between January 1992 and December 2008. They identified ASD diagnoses for twins in the STR, with follow-up to 2013, and used questionnaires to assign screening diagnoses of ASD to CATSS participants and to assess autistic traits.

Data reference: Taylor MJ, et al. JAMA Psychiatry. 2020;doi:10.1001/jamapsychiatry.2020.0680.

Taylor and colleagues divided each sample into multiple birth cohorts spanning 1982 to 1991 for STR only, as well as 1992 to 1995, 1996 to 1999, 2000 to 2003, and 2004 to 2008. They assessed whether changes occurred in birth cohorts in environmental and genetic factors. underlying variance in autism traits, as well as the relative contribution of genetics and environment to autism causation.

The analysis included data from 22,678 pairs of twins in the STR and 15,280 pairs in the CATSS. The results showed that the heritability of screening diagnoses ranged from 0.75 (95% CI, 0.58-0.87) to 0.93 (95% CI, 0.84-0.98) among CATSS participants and 0.88 (95% CI, 0.74-0.96) to 0.97 (95% CI, 0.74-0.96). , 0.89-0.99) among STR participants. The researchers observed a modest increase in the variance of autistic traits over time, associated with increases in environmental and genetic variance, with the total variance increasing from 0.95 (95% CI, 0.92-0, 98) at 1.17 (95% CI, 1.13-1.21). ) over time.

“Our results do not reject the role of environmental factors in ASD and are consistent with previous studies suggesting that these factors are likely to be unshared rather than shared,” the researchers wrote. “Non-shared environmental factors contribute to differences between parents sharing the same household (e.g., birth weight in association with ASD).” – by Joe Gramigna

Disclosures: One study author reports grants from the Swedish Research Council while conducting the study, and another study author reports grants and personal fees from Shire/Takeda and personal fees from Evolan in outside of the submitted work. The other authors report no relevant financial information.

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