Prevalence of Autism Spectrum Disorder and Co-morbidities in Children and Adolescents: A Systematic Literature Review

Abstract

Objective: Individuals with autism spectrum disorder often present somatic and/or psychiatric co-morbid disorders. The DSM-5 allows for consideration of additional diagnoses besides ASD and may have impacted the prevalence of co-morbidities as well as being limited in capturing the true differences in prevalence observed between males and females. We describe the prevalence of ASD and frequently observed co-morbidities in children and adolescents (<18 years) in the United States and five European countries. Methods: Two systematic literature reviews were conducted in PubMed and Embase for the period 2014-2019 and focusing on the prevalence of ASD and nine co-morbidities of interest based on their frequency and/or severity: Attention Deficit Hyperactivity Disorder (ADHD), anxiety, depressive disorders, epilepsy, intellectual disability (ID), sleep disorders, sight/hearing impairment/loss, and gastro-intestinal syndromes (GI). Results: Thirteen studies on prevalence of ASD and 33 on prevalence of co-morbidities were included. Prevalence of ASD was 1.70 and 1.85% in US children aged 4 and 8 years respectively, while prevalence in Europe ranged between 0.38 and 1.55%. Additionally, current evidence is supportive of a global increase in ASD prevalence over the past years. Substantial heterogeneity in prevalence of co-morbidities was observed: ADHD (0.00-86.00%), anxiety (0.00-82.20%), depressive disorders (0.00-74.80%), epilepsy (2.80-77.50%), ID (0.00-91.70%), sleep disorders (2.08-72.50%), sight/hearing impairment/loss (0.00-14.90%/0.00-4.90%), and GI syndromes (0.00-67.80%). Studies were heterogeneous in terms of design and method to estimate prevalence. Gender appears to represent a risk factor for co-morbid ADHD (higher in males) and epilepsy/seizure (higher in females) while age is also associated with ADHD and anxiety (increasing until adolescence). Conclusion: Our results provide a descriptive review of the prevalence of ASD and its co-morbidities in children and adolescents. These insights can be valuable for clinicians and parents/guardians of autistic children. Prevalence of ASD has increased over time while co-morbidities bring additional heterogeneity to the clinical presentation, which further advocates for personalized approaches to treatment and support. Having a clear understanding of the prevalence of ASD and its co-morbidities is important to raise awareness among stakeholders.

Keywords: Autism Spectrum Disorder; autism; co-morbidities; pediatric; prevalence; review.

Figure 1

Trends in prevalence of ASD. Myers et al. (21) [a] and [b] include the results from the CDC data set and clinically diagnosed data set, respectively; Yong et al. (22) [a] and [b] include results for the age group 5 to 12 and 13 to 17, respectively. Age of the population considered: 4 year-olds: Christensen et al. (15); 7 year-olds: van Bakel (23); 8 year-olds: Myers et al. (21); van Naarden Braun (24); 5-17 year-olds: Yong et al. (22); 0-24 year-olds: Murray (25), Bachman et al. (20).

Figure 2

PRISMA diagram prevalence of co-morbidities in ASD.

Figure 3

ADHD prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 4

Anxiety prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 5

Depressive disorders prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 6

Epilepsy prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 7

GI prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 8

Hearing prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 9

Intellectual disability prevalence estimates. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 10

Sleep disorder prevalence estimate. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.

Figure 11

Vision impairment prevalence estimate. Each point reports a prevalence estimate for the related comorbidity. Studies with more than one data point indicate the estimate of the prevalence among different subgroup of the population. See Supplementary Table 4 for the description of the population used in each study. Sample sizes are shown in brackets above each study label. Orange mark: Female population only; Green mark: Male population only; Black mark: No sex distinction.