Genetic and Environmental Epidemiology of Autism Spectrum Disorder: A Critical Gap of Interest in Global Psychiatry

Abstract

Recently, the lack of evidence regarding primary data on the epidemiology of autism spectrum disorder (ASD) in Brazil has been highlighted. The discussion underscores the concerning rise in autism diagnoses over recent decades, based on data from the United Kingdom. Although various factors have been proposed to explain this phenomenon, much of the available information remains inconclusive and restricted to specific geographic regions. This raises concerns about the validity of published findings, given the reported influence of genetic and environmental factors, both of which are key risk determinants for ASD and vary across regions and populations.

Dear Editor,

Recently, Dellazari et al. (1) addressed the gap in evidence regarding primary data on the epidemiology of autism spectrum disorder (ASD) in Brazil. Their analysis highlights the alarming increase in autism diagnoses over the past decades, as indicated by data originating from the United Kingdom (2). Although various factors have been proposed to explain this phenomenon, much of the existing information remains inconclusive and limited to specific geographic regions (3). This raises concerns about the validity of published results, given the reported influence of genetic and environmental factors, both of which are significant risk determinants for ASD (3, 4) and vary across regions and populations.

Dellazari et al. (1) elegantly summarized the existing epidemiological evidence in Brazil concerning ASD prevalence. Notably, existing studies have primarily focused on broader categories of mental and psychiatric disorders, particularly among children and adolescents (1). However, these studies do not provide in‐depth analyses of variables related to the incidence, prevalence, progression, and outcomes within this population. This reveals an even larger knowledge gap while simultaneously presenting a valuable opportunity for research with significant implications for clinical practice and community health.

To assess the magnitude of the gap in epidemiological studies on ASD in Brazil compared to the region (Latin America) and the world, and to provide specific data on research trends over time, an exploratory scientometrics analysis was conducted using the Scopus, PubMed, and Web of Science databases. To ensure precise results on the availability of epidemiological studies focused on describing factors related to the health and disease patterns associated with ASD, only the title tag was used.

To standardize the analysis, as the three databases record different metadata, only the database yielding the highest number of results was used. The term officially listed in the Medical Subject Headings (MeSH), under the title and explicit definition of “Autism Spectrum Disorder” (MeSH Unique ID: D000067877), was employed. This term has only one officially registered synonym, “Autistic Spectrum Disorder,” which was also included. Additional details and the validity of this type of analysis have been described previously (5).

Reproducing the search revealed that Scopus contained the highest number of published scientific documents globally (n = 34), compared to PubMed (n = 7) and Web of Science (n = 14). Consequently, Scopus was selected for the analysis. The search strategy employed was as follows: TITLE(Epidemiology) OR TITLE(“Genetic Epidemiology”) OR TITLE(“Environmental Epidemiology”) AND TITLE(“Autism Spectrum Disorder”) OR TITLE(“Autistic Spectrum Disorder”). Search was conducted on January 20, 2025.

To focus on primary data, only scientific documents classified as original articles were considered. A manual review of the 34 results identified only three studies (6, 7, 8) with specific epidemiological designs (prevalence studies) aimed at exploring prevalence and related characteristics exclusively in individuals with ASD (6, 7, 8).

These three studies were conducted in high‐income countries (Portugal (6), the United Kingdom (7), and the United States (8)) and focused, respectively, on adolescents (6), adults (7), and young individuals (8). However, the studies are limited to estimating prevalence and describing general human characteristics in clinical and community settings. They did not investigate potential risk factors, predictors, or prognostic outcomes specific to this population. Notably, the first of these studies was published in 2007, and nearly two decades later, the evidence remains sparse. Epidemiological studies with primary data on ASD account for <10% of the available literature on this topic (n = 3/34; 8.8%).

Notably, the remaining documents (n = 31) consist of reviews, book chapters and short documents (Figure 1), which derive their epidemiological estimates from secondary data, often based on global burden of diseases studies, with some being outdated by more than a decade.

FIGURE 1.

Distribution of publication types on the epidemiology of autism spectrum disorder in Scopus (2002–2024) (N = 34 documents). Search was conducted on January 20, 2025.

Genetic studies have identified several unusual de novo mutations with significant implications for polygenic risk, epigenetics (a modifiable factor over time), and gene‐by‐environment interactions (9). These findings, highlighted over 2 decades ago, emphasized the importance of conducting longitudinal translational studies to identify variables with the greatest impact on the risk of developing ASD (9). However, the observed trends in scientific publications demonstrate substantial limitations in addressing this call to action.

It can therefore be inferred that genetic and environmental epidemiology in ASD remains a critical and underexplored topic that deserves greater attention within global psychiatry. This aligns with various standards of relevance and pluralism in medical research (10), underscoring the need to provide primary data evidence to enhance evidence‐based decision‐making in clinical, community, and scientific contexts concerning ASD.

This issue does not reflect merely a local research gap but represents an international opportunity that highlights the necessity for multidisciplinary collaboration in global psychiatry.