Abstract
Background
Children and adolescents with intellectual disability (ID) frequently experience various comorbid psychiatric symptoms. However, research on the comorbidity of psychiatric disorders in this population remains limited. In this study, we aimed to comprehensively examine the prevalence of psychiatric disorders among children and adolescents with ID in South Korea from 2012 to 2021.
Methods
We obtained data from the National Health Insurance Service-National Health Information Database (NHIS-NHID) on individuals aged 2–18 years who were diagnosed with ID (F70–F79.9) between 2012 and 2021. Psychiatric disorders were identified using the following the International Classification of Diseases, 10th Edition codes: attention-deficit/hyperactivity disorder (ADHD) (F90), autism spectrum disorder (ASD) (F84), language disorder (F80), tic disorders (F95), anxiety disorders (F401–F402, F410–F411, F930–F932), depressive disorder (F32, F33), conduct disorder (F918, F928, F911), and oppositional defiant disorder (ODD) (F913). We analyzed the annual prevalence of comorbid psychiatric disorders.
Results
Throughout the study period, males consistently outnumbered females (62.6–65.5% vs. 34.5–37.4%). ADHD had the highest prevalence among psychiatric disorders, increasing from 30.23% in 2012 to 41.77% in 2021. Similar increasing trends were observed for ASD (10.95–15.46%) and depression (10.46–19.37%). Significant sex differences were observed in most disorders: ADHD, ASD, tic disorders, language disorder, conduct disorder, and ODD showed male predominance (P < 0.001), while depressive disorder showed female predominance (P < 0.01). Anxiety disorders showed no significant sex differences.
Conclusion
This study enhances our understanding of the epidemiology of psychiatric comorbidities in South Korean children and adolescents with ID. The evaluation of comorbid psychiatric disorders in this population is crucial for prognosis, with particular attention needed for ADHD and depressive disorder due to their relatively high prevalence. Future research should focus on preventing and treating psychiatric comorbidities in children and adolescents with ID.
Keywords: Intellectual Disability, Children, Adolescents, Prevalence, Psychiatric Disorder
Graphical Abstract
INTRODUCTION
Intellectual disability (ID) is characterized by deficits in intellectual functioning and adaptive behavior, affecting conceptual, social, and practical domains from early developmental stages.1 The global prevalence of ID is estimated to be 1–3% of the population.2 According to the disability registration report released by the Ministry of Health and Welfare in South Korea, 229,511 individuals with ID have been registered, accounting for 8.7% of all registered persons with disabilities. Among them, 45,819 were children and adolescents under the age of 19, comprising 19.96% of the total ID population.3
Individuals with ID have a high prevalence of comorbid psychiatric disorders, including depressive disorders, anxiety disorders, autism spectrum disorder (ASD), and attention-deficit/hyperactivity disorder (ADHD).4 In a population-representative sample in the US, Paltt et al.5 reported that 65.1% of adolescents with ID met the lifetime criteria for a psychiatric disorder. A previous systematic review estimated that the prevalence of psychiatric symptoms among children and adolescents with ID ranged from 38% to 49%, with ADHD, conduct disorder, and anxiety disorder6 being the most common comorbidities. Children with ID were found to have twice the rate of diagnosable psychiatric disorders compared to their peers without ID.7 These psychiatric comorbidities complicate developmental trajectories, significantly reduce quality of life, and place additional burdens on caregivers, educators, and healthcare systems.8
Despite recognition of the importance of understanding psychiatric comorbidities in children and adolescents with ID, these disorders are often underdiagnosed and undertreated. Most existing research has focused on adults with ID, while studies on children and adolescents are limited. Previous studies on ID and psychopathology have often been based on non-representative populations. Research on the prevalence of psychiatric comorbidities in ID has been conducted in South Korea, reporting that 89.24% of subjects had one or more psychiatric disorders. However, these studies primarily focused on adults with ID, making it difficult to track changes in prevalence over time.8 In South Korea, comprehensive epidemiological studies investigating psychiatric comorbidities among children and adolescents with ID remain scarce. The lack of basic epidemiological data hinders the development of appropriate diagnostic and treatment strategies for these conditions.
In the present study, we aimed to conduct a nationwide investigation of the prevalence, characteristics, and temporal trends of psychiatric comorbidities in children and adolescents with ID in South Korea. The findings of this study are expected to support the development of policies and clinical practices that enhance mental health management and strengthen support systems for this population.
METHODS
Study design and data source
This retrospective study utilized data from the National Health Insurance Service-National Health Information Database (NHIS-NHID) of South Korea from January 1, 2012, to December 31, 2021. The NHIS-NHID is a comprehensive public health database for the South Korean population that includes information on healthcare utilization, diagnoses, prescriptions, health screenings, and sociodemographic factors. Diagnoses in the database are coded according to the International Classification of Diseases, 10th Edition (ICD-10).
Study population
The study population comprised children and adolescents aged 2–18 years who had been diagnosed with ID at least twice, with ICD-10 codes F70–F79.9, recorded as either a principal or secondary diagnosis. The final study population included children and adolescents diagnosed with ID between 2012 and 2021, with annual cohorts ranging from 10,638 to 14,587 participants.
Study variables
Baseline characteristics included sex, age at first diagnosis, and ID severity, which was classified into five categories: mild (F70), moderate (F71), severe (F72), profound (F73), and other/unspecified (F78–F79). Age was categorized into three groups: 2–6 years, 7–11 years, and 12–18 years.
Socioeconomic status was assessed based on household income and type of insurance. For household income, we used the National Health Insurance Service (NHIS) premium contribution levels, which allocate every household to one of 20 levels (ventiles) based on both earned income and assets, serving as a comprehensive proxy for economic status. These 20 levels were regrouped into four categories for analysis: low (levels 1–7), medium-low (8–13), medium-high (14–16), and high (17–20). Individuals receiving Medical Aid were classified separately. Medical Aid is a public assistance program for people with very low income (approximately the bottom 3% of the population) and differs from the National Health Insurance in that it provides nearly full medical coverage without requiring premium payments. Missing household income data were included in the analyses without imputation or adjustments.
Residential areas were classified as urban or rural according to administrative divisions, with special metropolitan cities categorized as urban.
Comorbid psychiatric disorders
Comorbid psychiatric disorders were identified on the basis of at least one recorded diagnosis. These included ADHD (F90), ASD (F84), language disorder (F80), tic disorders (F95), and anxiety disorders, including separation anxiety disorder (F930), specific phobia (F402, F931), social anxiety disorder (F401, F932), panic disorder (F410), generalized anxiety disorder (F411), and other anxiety disorders (F41, F93). Additional disorders included depressive disorder (F32, F33), conduct disorder (F918, F928, F911), and oppositional defiant disorder (ODD; F913).
Statistical analysis
The annual prevalence was calculated by dividing the number of diagnosed cases of each psychiatric disorder by the total number of ID patients each year. Categorical variables are presented as frequencies and percentages, and continuous variables are expressed as means with standard deviations. Sex differences in prevalence were assessed using the chi-square test. Male-to-female prevalence ratios (M/F ratios) were calculated for each disorder and year. Temporal trends in prevalence rates were analyzed over the study period (2012–2021) for both overall prevalence and sex-specific patterns. All analyses were performed using SAS version 9.4 (SAS Institute, Cary, NC, USA), with statistical significance set at P < 0.05.
Ethics statement
The study was granted an exemption from full review by the Institutional Review Board of Jeju University Hospital (JEJUNUH 2024-10-013) due to the use of de-identified data, waiving the requirement for informed consent.
RESULTS
Participant characteristics
During the study period (2012–2021), males consistently outnumbered females (62.6–65.5% vs. 34.5–37.4%). The mean age at first diagnosis increased slightly from 12.14 ± 4.14 years in 2012 to 12.81 ± 3.99 years in 2021. The age distribution showed notable changes: the proportion of patients aged 2–6 years decreased from 25.3% to 23.8%, whereas that of the 12–18-year age group declined from 46.3% to 40.5%. Regarding ID severity, the proportion of mild ID cases increased from 36.0% to 48.9%, whereas that of severe ID (19.4% to 10.4%) and profound ID (6.3% to 2.4%) decreased over the study period (Table 1).
Table 1. Demographic characteristics of the study participants.
| Variables | Year | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2012 | 2013 | 2014 | 2015 | 2016 | 2017 | 2018 | 2019 | 2020 | 2021 | ||
| Total No. | 14,587 | 13,830 | 12,319 | 11,862 | 13,176 | 12,130 | 11,724 | 11,952 | 10,971 | 10,638 | |
| Sex | |||||||||||
| Male | 2,579 (63.5) | 2,275 (62.6) | 2,016 (63.9) | 1,932 (64.7) | 2,070 (65.5) | 1,828 (64.9) | 1,850 (65.5) | 1,776 (64.3) | 1,416 (63.6) | 1,121 (64.6) | |
| Female | 1,482 (36.5) | 1,358 (37.4) | 1,140 (36.1) | 1,052 (35.3) | 1,089 (34.5) | 988 (35.1) | 974 (34.5) | 988 (35.7) | 811 (36.4) | 613 (35.4) | |
| Age at first diagnosis, yr | 12.14 ± 4.14 | 12.25 ± 4.18 | 12.28 ± 4.31 | 12.42 ± 4.34 | 12.67 ± 4.28 | 12.51 ± 4.30 | 12.38 ± 4.33 | 12.39 ± 4.27 | 12.54 ± 4.19 | 12.81 ± 3.99 | |
| Age group, yr | |||||||||||
| 2–6 | 1,029 (25.3) | 1,022 (28.1) | 1,024 (32.4) | 972 (32.6) | 1,007 (31.9) | 886 (31.5) | 937 (33.2) | 822 (29.7) | 655 (29.4) | 412 (23.8) | |
| 7–11 | 1,150 (28.3) | 983 (27.1) | 830 (26.3) | 796 (26.7) | 853 (27.0) | 875 (31.1) | 919 (32.5) | 922 (33.4) | 734 (33.0) | 620 (35.8) | |
| 12–18 | 1,882 (46.3) | 1,628 (44.8) | 1,302 (41.3) | 1,216 (40.8) | 1,299 (41.1) | 1,055 (37.5) | 968 (34.3) | 1,020 (36.9) | 838 (37.6) | 702 (40.5) | |
| Severity of ID | |||||||||||
| Mild | 5,246 (36.0) | 5,113 (37.0) | 4,738 (38.5) | 4,806 (40.5) | 5,442 (41.3) | 5,329 (43.9) | 5,417 (46.2) | 5,707 (47.7) | 5,292 (48.2) | 5,203 (48.9) | |
| Moderate | 4,708 (32.3) | 4,451 (32.2) | 3,847 (31.2) | 3,622 (30.5) | 4,045 (30.7) | 3,587 (29.6) | 3,330 (28.4) | 3,284 (27.5) | 2,938 (26.8) | 2,815 (26.5) | |
| Severe | 2,837 (19.4) | 2,632 (19.0) | 2,195 (17.8) | 1,982 (16.7) | 2,075 (15.7) | 1,770 (14.6) | 1,485 (12.7) | 1,407 (11.8) | 1,192 (10.9) | 1,107 (10.4) | |
| Profound | 921 (6.3) | 802 (5.8) | 709 (5.8) | 653 (5.5) | 624 (4.7) | 487 (4.0) | 427 (3.6) | 369 (3.1) | 304 (2.8) | 250 (2.4) | |
| Others/unspecified | 875 (6.0) | 832 (6.0) | 830 (6.7) | 799 (6.7) | 990 (7.5) | 957 (7.9) | 1,065 (9.1) | 1,185 (9.9) | 1,245 (11.3) | 1,263 (11.9) | |
| Household incomea | |||||||||||
| Low ≤ 7 | 1,567 (38.6) | 1,487 (40.9) | 1,242 (39.4) | 1,176 (39.4) | 1,210 (38.3) | 1,146 (40.7) | 1,076 (38.1) | 1,072 (38.8) | 917 (41.2) | 680 (39.2) | |
| 7 < and ≤ 13 | 1,070 (26.3) | 925 (25.5) | 791 (25.1) | 746 (25.0) | 796 (25.2) | 707 (25.1) | 665 (23.6) | 651 (23.6) | 499 (22.4) | 400 (23.1) | |
| 13 < and ≤ 16 | 626 (15.4) | 549 (15.1) | 528 (16.7) | 473 (15.9) | 533 (16.9) | 452 (16.1) | 500 (17.7) | 446 (16.1) | 375 (16.8) | 320 (18.5) | |
| High > 16 | 774 (19.1) | 648 (17.8) | 569 (18.0) | 560 (18.8) | 604 (19.1) | 483 (17.2) | 550 (19.5) | 563 (20.4) | 413 (18.5) | 317 (18.3) | |
| Missing | 24 (0.6) | 24 (0.7) | 26 (0.8) | 29 (1.0) | 16 (0.5) | 28 (1.0) | 33 (1.2) | 32 (1.2) | 23 (1.0) | 17 (1.0) | |
| Insurance | |||||||||||
| Medical aidb | 779 (19.2) | 700 (19.3) | 554 (17.6) | 502 (16.8) | 569 (18.0) | 501 (17.8) | 484 (17.1) | 433 (15.7) | 384 (17.2) | 296 (17.1) | |
| Health insurance | 3,282 (80.8) | 2,933 (80.7) | 2,602 (82.4) | 2,482 (83.2) | 2,590 (82.0) | 2,315 (82.2) | 2,340 (82.9) | 2,331 (84.3) | 1,843 (82.8) | 1,438 (82.9) | |
| Residence | |||||||||||
| Urban | 2,686 (66.1) | 2,277 (62.7) | 2,047 (64.9) | 1,861 (62.4) | 2,032 (64.3) | 1,760 (62.5) | 1,755 (62.1) | 1,792 (64.8) | 1,417 (63.6) | 1,061 (61.2) | |
| Rural | 1,375 (33.9) | 1,356 (37.3) | 1,109 (35.1) | 1,123 (37.6) | 1,127 (35.7) | 1,056 (37.5) | 1,069 (37.9) | 972 (35.2) | 810 (36.4) | 673 (38.8) | |
Values are presented as number (%) or mean ± standard deviation.
‘Total No.’ and ‘Severity of ID’ were calculated based on all individuals diagnosed with ID in each year; all other demographic variables were calculated based on newly diagnosed cases within each year.
ID = intellectual disability.
aHousehold income categories based on NHIS premium levels (1–20 scale), commonly used as an income proxy in South Korea: Low (1–7); medium-low (8–13); medium-high (14–16); high (17–20). bMedical Aid recipients were analyzed separately as a very low-income group.
Prevalence of psychiatric disorders in children and adolescents with ID between 2012 to 2021
Among psychiatric disorders, ADHD showed the highest prevalence throughout the study period, with a steady increase from 30.23% in 2012 to 41.77% in 2021. ASD and depressive disorder also exhibited consistent increases in prevalence: ASD increased from 10.95% to 15.46%, whereas depressive disorder increased from 10.46% to 19.37%. The prevalence of anxiety disorders ranged from 2.71% to 5.25%. The prevalence of tic disorders doubled from 4.04% to 8.61% during the study period. The prevalence of language disorders remained relatively stable at approximately 9% throughout the study period. Conduct disorder and ODD, though remaining relatively low in prevalence, showed increasing trends (conduct disorder: 1.13–2.50%; ODD: 0.62–1.21%) (Table 2, Fig. 1).
Table 2. Overall annual prevalence of psychiatric disorder in children and adolescents with ID in Korea for each year between 2012 and 2021.
| Year | ADHD | ASD | Language disorder | Tic disorders | Anxiety disorders | Depressive disorder | Conduct disorder | ODD |
|---|---|---|---|---|---|---|---|---|
| 2012 | 4,409 (30.23) | 1,597 (10.95) | 1,327 (9.10) | 589 (4.04) | 395 (2.71) | 1,526 (10.46) | 165 (1.13) | 90 (0.62) |
| 2013 | 4,345 (31.42) | 1,576 (11.40) | 1,269 (9.18) | 632 (4.57) | 387 (2.80) | 1,520 (10.99) | 178 (1.29) | 71 (0.51) |
| 2014 | 4,023 (32.66) | 1,570 (12.74) | 1,161 (9.42) | 572 (4.64) | 349 (2.83) | 1,447 (11.75) | 168 (1.36) | 86 (0.70) |
| 2015 | 4,013 (33.83) | 1,565 (13.19) | 1,125 (9.48) | 529 (4.46) | 421 (3.55) | 1,596 (13.45) | 172 (1.45) | 86 (0.73) |
| 2016 | 4,115 (31.23) | 1,703 (12.93) | 1,156 (8.77) | 616 (4.68) | 456 (3.46) | 1,801 (13.67) | 201 (1.53) | 94 (0.71) |
| 2017 | 4,155 (34.25) | 1,598 (13.17) | 1,075 (8.68) | 686 (5.66) | 484 (3.99) | 1,904 (15.70) | 211 (1.74) | 100 (0.82) |
| 2018 | 4,302 (36.69) | 1,643 (14.01) | 1,111 (9.48) | 788 (6.72) | 491 (4.19) | 2,036 (17.37) | 216 (1.84) | 114 (0.97) |
| 2019 | 4,614 (38.60) | 1,763 (14.75) | 1,127 (9.43) | 877 (7.34) | 570 (4.77) | 2,161 (18.08) | 267 (2.23) | 124 (1.04) |
| 2020 | 4,375 (39.88) | 1,676 (15.28) | 1,010 (9.21) | 833 (7.59) | 539 (4.91) | 2,032 (18.52) | 268 (2.44) | 106 (0.97) |
| 2021 | 4,443 (41.77) | 1,645 (15.46) | 919 (8.64) | 916 (8.61) | 559 (5.25) | 2,061 (19.37) | 267 (2.50) | 129 (1.21) |
Values are presented as number (%).
ID = intellectual disability, ADHD = attention-deficit/hyperactivity disorder, ASD = autism spectrum disorder, ODD = oppositional defiant disorder.
Fig. 1. Total crude annual prevalence of psychiatric disorders in children and adolescents with intellectual disability in Korea, 2012–2021. (A) Prevalence of neurodevelopmental disorders. (B) Prevalence of anxiety disorders, depressive disorder, conduct disorder and oppositional defiant disorder.
ADHD = attention-deficit/hyperactivity disorder.
Annual prevalence of psychiatric disorders in children and adolescents with ID for each year according to sex
Most psychiatric disorders showed significant differences in prevalence between men and women throughout the study period (Table 3). Among neurodevelopmental disorders, ADHD had a consistently higher prevalence in males, with M/F ratios ranging from 1.39 to 1.51 (P < 0.001). ASD was also significantly more prevalent in males, with M/F ratios ranging from 1.47 to 1.72 (P < 0.001). Language disorders demonstrated moderate male predominance (M/F ratio: 1.13–1.42, P < 0.01), while tic disorders exhibited the highest male predominance (M/F ratio: 1.72–2.29, P < 0.001) (Table 3, Fig. 2).
Table 3. Sex differences in prevalence of psychiatric disorders among children and adolescents with ID between 2012 and 2021.
| Year | ADHD | ASD | Language disorder | Tic disorder | Anxiety disorders | Depressive disorder | Conduct disorder | ODD | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | Female | Male | M/F ratio | P value | |
| 2012 | 1,139 (22.62) | 3,270 (34.24) | 1.51 | < 0.001 | 380 (7.55) | 1,217 (12.74) | 1.69 | < 0.001 | 393 (7.80) | 934 (9.78) | 1.25 | < 0.001 | 137 (2.72) | 452 (4.73) | 1.74 | < 0.001 | 134 (2.66) | 261 (2.73) | 1.03 | 0.847 | 595 (11.82) | 931 (9.75) | 0.82 | < 0.001 | 38 (0.76) | 127 (1.33) | 1.75 | < 0.001 | 26 (0.52) | 64 (0.67) | 1.29 | 0.037 |
| 2013 | 1,181 (24.43) | 3,164 (35.18) | 1.44 | < 0.001 | 396 (8.19) | 1,180 (13.12) | 1.60 | < 0.001 | 408 (8.44) | 861 (9.57) | 1.13 | 0.002 | 145 (3.00) | 487 (5.41) | 1.80 | < 0.001 | 127 (2.63) | 260 (2.89) | 1.10 | 0.312 | 602 (12.45) | 918 (10.21) | 0.82 | < 0.001 | 42 (0.87) | 136 (1.51) | 1.74 | < 0.001 | 20 (0.41) | 51 (0.57) | 1.39 | 0.048 |
| 2014 | 1,077 (25.15) | 2,946 (36.66) | 1.46 | < 0.001 | 418 (9.76) | 1,152 (14.34) | 1.47 | < 0.001 | 339 (7.92) | 822 (10.23) | 1.29 | < 0.001 | 108 (2.52) | 464 (5.77) | 2.29 | < 0.001 | 124 (2.90) | 225 (2.80) | 0.97 | 0.743 | 556 (12.98) | 891 (11.09) | 0.85 | < 0.001 | 48 (1.12) | 120 (1.49) | 1.33 | 0.009 | 28 (0.65) | 58 (0.72) | 1.11 | 0.623 |
| 2015 | 1,033 (25.29) | 2,980 (38.32) | 1.51 | < 0.001 | 402 (9.84) | 1,163 (14.95) | 1.52 | < 0.001 | 346 (8.47) | 779 (10.02) | 1.18 | 0.003 | 100 (2.45) | 429 (5.52) | 2.25 | < 0.001 | 153 (3.75) | 268 (3.45) | 0.92 | 0.382 | 589 (14.42) | 1,007 (12.95) | 0.90 | 0.008 | 54 (1.32) | 118 (1.52) | 1.15 | 0.276 | 23 (0.56) | 63 (0.81) | 1.45 | 0.039 |
| 2016 | 1,090 (24.55) | 3,025 (34.63) | 1.41 | < 0.001 | 437 (9.84) | 1,266 (14.49) | 1.47 | < 0.001 | 339 (7.64) | 817 (9.35) | 1.22 | < 0.001 | 113 (2.55) | 503 (5.76) | 2.26 | < 0.001 | 160 (3.60) | 296 (3.39) | 0.94 | 0.456 | 675 (15.20) | 1,126 (12.89) | 0.85 | < 0.001 | 57 (1.28) | 144 (1.65) | 1.29 | 0.007 | 25 (0.56) | 69 (0.79) | 1.41 | 0.044 |
| 2017 | 1,078 (25.86) | 3,077 (38.65) | 1.49 | < 0.001 | 380 (9.12) | 1,218 (15.30) | 1.68 | < 0.001 | 289 (6.93) | 786 (9.87) | 1.42 | < 0.001 | 131 (3.14) | 555 (6.97) | 2.22 | < 0.001 | 160 (3.84) | 324 (4.07) | 1.06 | 0.487 | 693 (16.62) | 1,211 (15.21) | 0.92 | 0.007 | 59 (1.42) | 152 (1.91) | 1.35 | 0.009 | 31 (0.74) | 69 (0.87) | 1.18 | 0.367 |
| 2018 | 1,113 (27.91) | 3,189 (41.22) | 1.48 | < 0.001 | 408 (10.23) | 1,235 (15.96) | 1.56 | < 0.001 | 332 (8.33) | 779 (10.07) | 1.21 | < 0.001 | 169 (4.24) | 619 (8.00) | 1.89 | < 0.001 | 165 (4.14) | 326 (4.21) | 1.02 | 0.832 | 733 (18.38) | 1,303 (16.84) | 0.92 | 0.008 | 60 (1.51) | 156 (2.02) | 1.34 | 0.009 | 26 (0.65) | 88 (1.14) | 1.75 | < 0.001 |
| 2019 | 1,223 (30.27) | 3,391 (42.86) | 1.42 | < 0.001 | 430 (10.64) | 1,333 (16.85) | 1.58 | < 0.001 | 311 (7.70) | 816 (10.31) | 1.34 | < 0.001 | 188 (4.65) | 689 (8.71) | 1.87 | < 0.001 | 198 (4.90) | 372 (4.70) | 0.96 | 0.578 | 786 (19.46) | 1,375 (17.38) | 0.89 | < 0.001 | 77 (1.91) | 190 (2.40) | 1.26 | 0.006 | 25 (0.62) | 99 (1.25) | 2.02 | < 0.001 |
| 2020 | 1,166 (31.17) | 3,209 (44.39) | 1.42 | < 0.001 | 388 (10.37) | 1,288 (17.82) | 1.72 | < 0.001 | 307 (8.21) | 703 (9.72) | 1.18 | 0.003 | 183 (4.89) | 650 (8.99) | 1.84 | < 0.001 | 181 (4.84) | 358 (4.95) | 1.02 | 0.782 | 733 (19.59) | 1,299 (17.97) | 0.92 | 0.009 | 64 (1.71) | 204 (2.82) | 1.65 | < 0.001 | 17 (0.45) | 89 (1.23) | 2.73 | < 0.001 |
| 2021 | 1,169 (33.18) | 3,274 (46.02) | 1.39 | < 0.001 | 391 (11.10) | 1,254 (17.63) | 1.59 | < 0.001 | 271 (7.69) | 648 (9.11) | 1.18 | 0.004 | 205 (5.82) | 711 (9.99) | 1.72 | < 0.001 | 188 (5.34) | 371 (5.21) | 0.98 | 0.965 | 727 (20.64) | 1,334 (18.75) | 0.91 | 0.005 | 76 (2.16) | 191 (2.68) | 1.24 | 0.008 | 26 (0.74) | 103 (1.45) | 1.96 | < 0.001 |
Values are presented as number (%).
ID = intellectual disability, ADHD = attention-deficit/hyperactivity disorder, ASD = autism spectrum disorder, ODD = oppositional defiant disorder.
Fig. 2. Annual prevalence of neurodevelopmental disorders in child and adolescents with intellectual disability for each year between 2012 and 2021, stratified by sex.
Distinct patterns emerged for emotional and behavioral disorders. Depressive disorder consistently showed female predominance (M/F ratio: 0.82–0.92, P < 0.01), with the sex difference becoming more pronounced in recent years. Anxiety disorders were the only condition with no significant sex differences across most years (M/F ratio: 0.92–1.10, P > 0.05). Both conduct disorder and ODD showed male predominance, with conduct disorder showing decreasing sex differences over time (M/F ratio declining from 1.75 to 1.24, P < 0.01), while ODD demonstrated more variable sex differences (M/F ratio: 1.11–2.73, P values ranging from < 0.001 to > 0.05) (Table 3, Fig. 3).
Fig. 3. Annual prevalence of anxiety disorders, depressive disorder, conduct disorder and oppositional defiant disorder in child and adolescents with intellectual disability for each year between 2012 and 2021, stratified by sex.
DISCUSSION
The present study is the first to examine the prevalence of psychiatric disorders in children and adolescents with ID in South Korea. ADHD had the highest prevalence, ranging from 30.23% to 41.77%, followed by depressive disorder (10.46–19.37%) and ASD (10.95–15.46%). The prevalence of all psychiatric disorders gradually increased from 2012 to 2021. Neurodevelopmental disorders, conduct disorder, and ODD showed male predominance, whereas depressive disorder exhibited female predominance.
ADHD is the most prevalent comorbid condition among children with ID.7 The prevalence of ADHD in people with ID is 20% in clinical samples.9 Another study reported that ADHD was a common psychiatric disorder among children and adolescents with ID, with a prevalence of 39%.6 Consistent with these previous results, ADHD showed the highest prevalence, reported to be the highest at 30–40%, consistent with the findings of a previous study reporting ADHD was three times more prevalent in the ID group than in the typically developing group.10
ID and ASD frequently co-occur in clinical practice, but the comorbidity of ASD and ID varies depending on the study, with approximately 30–70% of children with ASD estimated to exhibit co-occurring ID,11 and approximately 28% of children with ID meeting the ASD criteria.12 A previous study reported the prevalence of ASD in ID as 18.04%,13 which is similar to the results of our study results. We found that ASD diagnoses have been increasing over the past 10 years, likely due to increased ASD knowledge and access to high-quality educational and medical services. ASD and ID are important neurodevelopmental disorders, and further research on their comorbidities is needed.
Compared to research on tic disorder and ADHD or ASD,14,15 there is relatively little research on tic disorder in ID. In this study, the prevalence of tics in children and adolescents with ID was reported to be 4–8%, which is higher than that in the general population. In a study of 9–13-year-olds with mild ID, language impairment was reported to be 54%,16 but the current study showed a relatively low and stable prevalence trend. Because the diagnosis and course of language disorders vary depending on development, prevalence rates may differ based on the target group and evaluation method. In addition to ADHD and ASD, further research is needed on comorbid neurodevelopmental disorders, such as tic and language disorders, which can affect daily life adaptive functioning. As with previous research results in the general population,17 the M/F ratio for the prevalence of neurodevelopmental disorders in this study was higher in males.
Emotional and behavioral problems are common among children and adolescents with ID. These age groups with ID experience adjustment problems and immense stress in their daily lives owing to a lack of emotional regulation and cognitive and behavioral coping strategies, leading to both emotional and externalizing problems. A previous study found that the prevalence of depression and/or anxiety problems in children and adolescents with ID was 35.4%, a rate generally comparable to that in typically developing peers.18 Another study reported an anxiety disorder prevalence of 11.4% and a depressive disorder prevalence of 1.4% in children and adolescents with ID.19 In contrast, the prevalence of depressive symptoms among Korean adolescents was 25.2% in 2020.20
In the current study, the prevalence of depressive disorders ranged from 10.46% to 19.37%, whereas that of anxiety disorders ranged from 2.71% to 5.25%. Depressive disorders were more prevalent than anxiety disorders and showed a rapid increase over the past decade. These findings suggest that children and adolescents with ID may experience more depressive symptoms than previously reported, highlighting the need for greater clinical attention to depressive disorders in this population. The M/F ratio for the prevalence of depressive disorder was higher in females, consistent with prior research.21
In a study targeting clinical samples, the prevalence of anxiety disorders, CD, and ODD in mild ID was 18.0%, CD 10.8%, and ODD 21.6%. In clinical settings, ADHD (64.9%), ODD (21.6%), and anxiety disorders (18.0%) were the most common comorbidities in school-aged children with mild ID.22 In the present study, the prevalence of anxiety disorders, CD, and ODD was lower than that reported in previous studies. Compared with previous studies, the present study included children and adolescents of all ages (aged 2–18 years), with 30% including those aged 2–5 years. In addition, because all ID severities were included, the rate of CD or ODD in the present study was lower than that in previous studies targeting school-aged children and adolescents or mild ID only. As the onset and presentation of psychiatric disorders in children and adolescents vary depending on the developmental period, future research that considers this is necessary. Consistent with previous studies, ODD and conduct disorder were more prevalent in males,19,20 and the M/F ratios for the prevalence of ODD and conduct disorder were predominantly higher in males.23
However, limitations should be considered when interpreting the present findings. First, ID cases may have been missed because diagnoses were identified solely using the NHIS-NHID database, excluding individuals with ID who were not seen in hospital departments. Nevertheless, the study benefits from nationwide data coverage and a large sample of South Korean children and adolescents with ID. Second, given our focus on establishing nationwide temporal trends in psychiatric comorbidity prevalence, we did not analyze associations between socioeconomic variables and psychiatric diagnoses. Future studies should examine the influence of socioeconomic factors and regional differences on psychiatric diagnostic patterns in children with ID. Furthermore, prospective studies are needed to investigate the factors associated with the diagnosis of comorbid psychiatric disorders in children and adolescents with ID. Third, we examined the prevalence of comorbid psychiatric disorders in children and adolescents with ID according to sex. A previous study suggested that the prevalence of comorbid psychiatric disorder of ID differs by age.7 However, we were unable to analyze the differences in prevalence according to age groups. Furthermore, given the significant decline in birth rates in Korea, the absolute number of children has decreased considerably, which may limit the interpretability of prevalence trends based solely on the proportion of psychiatric disorders among children with ID. Therefore, a long-term longitudinal study on the trends in the incidence of ID in relation to changes in birth rates, as well as the associated prevalence of psychiatric disorders, is highly necessary in South Korea. Future research should incorporate complementary indicators—such as incidence rates or age-standardized rates of intellectual disabilities based on the total population—and conduct age-stratified analyses to more accurately assess the impact of demographic changes on trends in psychiatric comorbidity.
The present study is the first to examine the prevalence of comorbid psychiatric disorders requiring clinical evaluation and treatment in children and adolescents with ID in South Korea. In this population, ADHD, ASD, and depressive disorder are highly comorbid. Clinicians should place greater emphasis on the evaluation and treatment of psychiatric comorbidities in children and adolescents with ID.
In conclusion, the present study offers new insights into the comorbidity of psychiatric disorders in children and adolescents with ID in South Korea and provides valuable epidemiological evidence for this population. Our findings underscore the critical importance of systematic screening and early intervention for children and adolescents with ID with psychiatric comorbidities. We believe that the evidence presented in this study may strengthen advocacy and governance for mental health promotion in this population and serve as a foundation for future policies aimed at improving access to mental health care. Future research on preventive measures, risk factors, disease progression, and outcomes of psychiatric disorders in children and adolescents with ID is warranted.
Footnotes
Funding: This work was supported by a research grant from Jeju National University Hospital (Jeju, Korea) in 2023 (grant number 2023-23). The funding body had no involvement in the study design; collection, management, analysis, and interpretation of data; or the decision to submit for publication.
Disclosure: The authors have no potential conflicts of interest to disclose.
- Conceptualization: Lee HJ.
- Data curation: Lee HJ, Kim JY.
- Formal analysis: Kim JY, Lee HJ, Kang NR.
- Funding acquisition: Lee HJ.
- Investigation: Joo MA, Kang NR.
- Methodology: Lee HJ, Joo MA, Kang NR.
- Software: Kim JY.
- Supervision: Lee HJ, Kang NR.
- Visualization: Kang NR.
- Writing - original draft: Joo MA, Kang NR, Lee HJ.
- Writing - review & editing: Joo MA, Kang NR, Lee HJ.
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