Predictors of age at diagnosis in autism spectrum disorders: the use of multiple regression analyses and a classification tree on a clinical sample

Autism spectrum disorders (ASD), according to The International Classification of Diseases, 10th Edition (ICD-10) [1], are neurodevelopmental conditions presenting with a range of symptoms, including impairment of communication, difficulties with social interaction, and atypical and limited patterns of behavior [2, 3].

The ASD umbrella includes autistic disorder, Asperger syndrome, pervasive developmental disorders not otherwise specified, and childhood disintegrative disorder [4]. Not only do these disorders have a significant effect on the quality of life, but they also have a considerable socioeconomic impact. The estimated global burden calculated as disability-adjusted life-years (DALY), which is an aggregation of years of life lost because of premature mortality and years lived with a disability, was 58 DALYs per 100,000 population for the autistic disorders and 53 DALYs per 100,000 for other ASDs [5].

The economic impact includes, among others, direct healthcare and special education costs and lost productivity for adults with ASD and their families/caregivers. Estimates of overall lifetime costs for individuals with ASD are in the millions of dollars, varying regionally [6].

In recent decades, we have seen a considerable increase in the reported prevalence of ASD, with recent estimates falling between 1 and 1.7%, according to studies conducted in the USA [7] and the UK [8]. No studies have specifically looked at the prevalence of autism in the Czech Republic; however, a comprehensive review of over 600 epidemiological studies worldwide (including also studies written in local languages like Arabic, Chinese, Dutch, French, etc.) did not identify regional differences in ASD prevalence, nor did it find that ethnic/cultural or socioeconomic factors had a substantial impact on prevalence [9].

It remains unclear whether the reported increase in ASD prevalence is due to an actual increase in the number of people who have autism, the result of better diagnostic tools and greater awareness, or a combination of both [10, 11]. Regardless of the cause, the increased numbers have led to a worldwide interest in studying ASD and its mechanisms.

An early autism diagnosis is essential for early intervention and treatment and enables patients to reach public support systems earlier, all of which are linked to a better prognosis, fewer autism symptoms over time, and better inclusion [10, 12]. On the other hand, delayed diagnoses are linked to increased parental stress and delays in treatments needed for better long-term trajectories [13]. Since identifying risk factors linked to delayed ASD diagnoses could potentially lead to a better diagnostic framework, it has been an area of interest in recent years.

A comprehensive review of 42 studies, written in English, published between 1990 and 2012, and indexed in PubMed, showed that higher socioeconomic status, symptom severity, and greater parental concern were associated with an earlier diagnosis [14]. The vast majority of the reviewed studies found no association between the sex of the child and age at ASD diagnosis. Furthermore, this critical and high-quality review looked at possible causes for delayed ASD diagnoses and unsurprisingly found that Asperger syndrome tends to be diagnosed at older ages than other types of ASD [14].

A 2021 Danish study supported the idea that the age at diagnosis varies relative to the subtype of ASD diagnosis and that atypical autism, Asperger syndrome, and pervasive developmental disorders not otherwise specified tend to be diagnosed at older ages [15]. This study also found an association between delayed ASD diagnosis and low parental education; however, only when compared to a group of patients that received an early autism diagnosis, not when compared to a control group with no ASD diagnosis. Lastly, this study found that being diagnosed with ADHD, language, developmental, or emotional disorders were risk factors for a delayed ASD diagnosis. The strongest association was seen in children with a previous diagnosis of ADHD [15].

In the Czech Republic, the diagnostic process of autism occurs in various settings. Two university departments (our Department of Child Psychiatry in Prague and the Department of Child Neurology in Brno) provide a diagnosis of autism during short-term hospitalizations requiring a referral from a pediatrician, child psychiatrist, neurologist, or clinical child psychologist. The process includes comprehensive assessment (e.g., psychiatric examination supplemented by specific diagnostic tools for autism, genetic examination, and an EEG). Diagnosis of autism is also provided by many but not all child psychiatrists and clinical child psychologists as outpatient care. Starting in 2016, all primary care pediatricians were obliged to begin screening all children aged 18 months for autism. All these assessments are covered by general health insurance, are free of charge, and all families are supposed to have equal access to the facilities. Besides these, services based on private payments are offered by some private providers in major towns, and we can assume they target high-income families. Regardless of the payment type, all services are generally limited by the small number of child psychiatrists with expertise in autism, which contributes to long waiting times. Due to COVID-19, waiting times now range from 1 to 2 years.

In our previous study of 160 children, we found that the ASD diagnosis age correlated negatively with maternal and paternal ages at the time of birth of the ASD child as well as with paternal and maternal education. However, it did not correlate with socioeconomic status or the number of ASD information resources available to the parents [16].

In this study, we enrolled new participants and broadened the cohort to 324 children aged 2 to 16 years. The aim of our study was to further explore the association between age at diagnosis and demographic variables, such as socioeconomic status, parental education level, age of parents, the Autism Diagnostic Observation Schedule (ADOS) scores, and intellectual disabilities.

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