Search This Blog

Saturday, May 9, 2020

Genetics Matters More Than Environment

In The Politics of Autism, I discuss various ideas about what causes the condition. Many posts have discussed the potential correlatesrisk factors, and possible causes that have been the subject of serious studies:

Mark J. Taylor and colleagues have an article at  JAMA Psychiatry titled "Etiology of Autism Spectrum Disorders and Autistic Traits Over Time." The abstract:
Key Points
Question Has association between genetic factors and autism spectrum disorders (ASDs) changed over time?

Findings In this study, data were available from 2 twin cohorts, one born between 1982 and 2008 (n = 22 678 pairs) and the other between 1992 and 2008 (n = 15 279 pairs). Genetic factors were associated with ASD and autistic traits and the relative importance of these factors was consistent over time, whereas environmental factors played a smaller role.

Meaning Environmental factors associated with ASD have not increased in importance over time and are unlikely to explain the apparent increase in the prevalence of ASD.

Importance The frequency with which autism spectrum disorders (ASDs) are diagnosed has shown a marked increase in recent years. One suggestion is that this is partly because of secular changes in the environment, yet to our knowledge this hypothesis lacks evidence.

Objective To assess whether the relative importance of genetic and environmental associations with ASD and autistic traits has changed over a 16-year and 26-year period.

Design, Setting, and Participants A twin design was used to assess whether the heritability of ASD and autistic traits has changed over time. Data from 2 nationwide Swedish twin cohorts was used: the Swedish Twin Registry (STR; participants born between January 1982 and December 2008) and the Child and Adolescent Twin Study in Sweden (CATSS; participants born between January 1992 and December 2008). Autism spectrum disorder diagnoses were identified for twins in the STR, with follow-up to 2013. Questionnaires assigned screening diagnoses of ASD to CATSS participants and assessed autistic traits. Analyses were performed from September 1, 2018, to March 31, 2019.

Exposures Each sample was divided into several birth cohorts covering 1982 to 1991 (for the STR only), 1992-1995, 1996-1999, 2000-2003, and 2004-2008.

Outcomes We assessed whether the genetric and environment variance underlying autistic traits changed across birth cohorts and examined whether the relative contribution of genetics and environment to liability for autism changed across birth cohorts.

Results Data were available for 22 678 twin pairs (5922 female same-sex pairs [26.1%], 5563 male same-sex pairs [24.5%], and 11193 opposite-sex pairs [49.4%]) in the STR and 15 280 pairs (4880 female same-sex pairs [31.9%], 5092 male same-sex pairs [33.3%], and 5308 opposite-sex pairs [34.7%]) in CATSS. The heritability of ASD diagnoses in the STR ranged from 0.88 (95% CI, 0.74-0.96) to 0.97 (95% CI, 0.89-0.99). The heritability of screening diagnoses in CATSS varied from 0.75 (95% CI, 0.58-0.87) to 0.93 (95% CI, 0.84-0.98). Autistic traits showed a modest variance increase over time that was associated with increases in genetic and environmental variance, with the total variance increasing from 0.95 (95% CI, 0.92-0.98) to 1.17 (95% CI, 1.13-1.21) over time.

Conclusions and Relevance Weak evidence was found for changes in the genetic and environmental factors underlying ASD and autistic traits over time. Genetic factors played a consistently larger role than environmental factors. Environmental factors are thus unlikely to explain the increase in the prevalence of ASD.
A release from the University of Texas at Austin:
A mother's use of antidepressants during pregnancy does not appear to increase her child's risk for autism, according to a new meta-analysis by Jeffrey Newport, M.D., published in The American Journal of Psychiatry.
Newport is director of the Women's Reproductive Mental Health program at UT Health Austin's Mulva Clinic for the Neurosciences and a professor of psychiatry at Dell Medical School at The University of Texas at Austin.
He examined 14 studies, many of which identified a connection between prenatal antidepressant use and autism. However, Newport says that research failed to account for ascertainment bias, which occurs when one group of patients or subjects is tested more frequently than others.
In the analysis, Newport found the root of bias is limited access to health care among ethnic minority and immigrant mothers.
"In these studies, immigrant and Latina mothers consistently had both lower rates of antidepressant treatment and lower rates of autism diagnosis in their children," Newport said. "This is not surprising, as these minority groups are known to have poorer access to health care, including treatment for depression and careful diagnostic assessment of concerning behaviors in a child."
Newport discovered that family-based studies eliminated the bias problem by comparing children with antidepressant exposure or autism diagnosis with their siblings who did not have antidepressant exposure or autism. With the ethnic bias eliminated, the family-based studies revealed no association between prenatal antidepressant use and autism.
"This should remind us that although insurance databases and national registries have the advantage of huge numbers of participants, their data is not collected to answer research questions, but to manage business and clinical concerns," Newport said. "Thankfully, the results of this meta-analysis show that with thoughtful study designs, researchers can overcome the biases often encountered when using such databases."