Abstract
Background:
Adults with autism spectrum disorder (ASD) show wide variation in daily functioning. Disability assessment in practice often relies on measures of symptom severity, although the extent to which symptom severity reflects functional disability in adulthood remains unclear. We examined the association between autism symptom severity and functional disability in adults with ASD using the Indian Scale for Assessment of Autism (ISAA) and the World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0).
Methods:
This cross-sectional study included 78 adults with ASD recruited from clinical and community-based service settings. Autism symptom severity and functional disability were assessed using ISAA and WHODAS 2.0, respectively. Associations were examined using Spearman’s correlation and multivariable linear regression, adjusting for age and co-occurring intellectual and developmental disability.
Results:
ISAA total scores strongly correlated with WHODAS 2.0 scores (ρ = 0.83, p < .001). WHODAS scores increased across ISAA severity categories (19.22 ± 8.74 vs. 36.53 ± 10.74 vs. 52.29 ± 8.03; p < .001). In multiple regression analysis, autism severity (B = 0.46, p < .001) and co-occurring intellectual disability (B = 6.55, p = .017) remained significant independent predictors of functional disability, explaining 69.6% of the variance (adjusted R2 = 0.696).
Conclusion:
Autism severity was strongly associated with functional disability in adulthood; however, it did not fully account for real-world functioning. These findings underscore the multidimensional nature of disability and support the need for incorporating broader, function-focused assessment tools in adult disability evaluation.
Question: How well does symptom severity reflect functional disability in adults with autism? Findings: Greater symptom severity is associated with higher functional disability, but symptom-based scores do not fully account for real-world functioning, even after adjusting for comorbid intellectual disability. Meaning: Relying solely on symptom severity may miss important aspects of adult functioning, underscoring the need for function-focused approaches in disability assessment and service planning.Key Message:
Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by impairment in social communication, restricted interests, and repetitive behaviors. An estimated 78 million individuals with autism live worldwide, highlighting its global significance. 1 Persons with autism show a wide range of cognitive abilities, adaptive skills, language abilities, and support needs, resulting in highly diverse clinical presentations. These abilities and needs often change over time. 2 Some adults with autism require substantial support throughout life, while others live and work independently. Despite advances in understanding the neurobiology of autism and the development of evidence-based interventions, adults with autism frequently have complex and evolving needs across healthcare, education, employment, and social services. Comprehensive disability assessment is therefore essential for long-term care and policy planning. 3
According to the World Health Organization’s International Classification of Functioning, Disability and Health (ICF), disability is a dynamic interaction among biological, personal, and environmental factors, rather than a consequence of a health condition. The ICF emphasizes how health conditions affect a person’s capacity to function in daily life by focusing on participation and activity limitations rather than on diagnosis alone. 4
Under the Rights of Persons with Disabilities (RPwD) Act 2016, the Government of India recognizes ASD as one of 21 specified disabilities. However, a clinical diagnosis of persons with ASD does not automatically confer eligibility for government support in education, employment, or social security. Access to these provisions is contingent upon certification as having a “benchmark disability,” defined as 40% or above disability, as measured by a designated medical board using standardized, government-notified assessment tools, establishing a critical distinction between a clinical diagnosis and legal eligibility for state-mandated benefits.5,6 Indian Scale for Assessment of autism (ISAA) is the only mandated tool for measuring disability in children and adults with AD under the RPwD Act, 2016.7–9 The ISAA was adapted from the Childhood autism Rating Scale (CARS), a widely used tool for assessing autism in children, and was modified to suit the sociocultural and clinical context in India. ISAA has been validated in children with a mean age of 9 years; however, it has not been validated in adults. 7 While ISAA provides a structured assessment of symptom severity, its application in disability evaluation is less studied, particularly in adults, where symptom expression may change with age and interventions. 10 Household responsibilities, employment, financial responsibilities, and intimate or sexual relationships are central to community participation and functioning in adulthood. Such domains may not be adequately captured by a symptom severity-based tool like ISAA. As a result, adults with ASD who experience significant functional impairments may be under-identified and risk exclusion from disability-related support systems. Comorbid conditions, such as intellectual disability(IDD), attention-deficit/hyperactivity disorder (ADHD), epilepsy, anxiety, and depression, are common in autism and can further increase functional challenges and impact quality of life.11,12
The World Health Organization Disability Assessment Schedule 2.0 (WHODAS 2.0) is a standardized, cross-culturally validated tool that aligns with the ICF. It measures functional disability across six domains, independent of diagnosis, and emphasizes participation restrictions and activity limitations rather than symptom presence.13–15
Although ISAA and WHODAS 2.0 have clinical and policy relevance, empirical evidence on the relationship between autism symptom severity and functional disability remains limited, especially in adults. The present study, therefore, examines the association between ISAA scores and WHODAS 2.0–derived functional disability in a sample of adults with autism to improve understanding of how symptom severity relates to functional outcomes in adulthood.
Methods
Study Design and Setting
This cross-sectional study was conducted at a tertiary care neuropsychiatric center in Bengaluru, Karnataka, India. Participants were recruited from outpatient clinics, inpatient units, a hospital-based psychiatric rehabilitation daycare program, and community-based vocational and rehabilitation centers. Data were collected between October 2023 and June 2024. The Institutional Ethics Committee approved the study.
Participants
Seventy-eight adults aged 18 years and above with a clinically confirmed diagnosis of ASD with or without comorbid IDD were included. Diagnoses were confirmed through clinical records and/or a Unique Disability ID (UDID) card issued by the Government of India under the autism category. Diagnoses were based on clinical documentation consistent with ICD-10 (pervasive developmental disorder) or ICD-11 (ASD) criteria. To enhance diagnostic consistency across settings, the investigator reviewed diagnostic details from clinical records and interviews and included only participants with clearly documented and concordant diagnoses.
The required sample size was calculated assuming a minimum correlation coefficient of 0.75 between ISAA and WHODAS 2.0, with a margin of error of ±0.1 and a 95% confidence level. Based on this calculation, a sample of 78 participants was deemed adequate to meet the study’s analytical objectives.
Instruments
Participant characteristics were captured via a custom sociodemographic questionnaire that recorded age, socioeconomic status, clinical history, and possession of a UDID card. Disability was quantified using two primary instruments: The ISAA and the WHODAS 2.0. The ISAA consists of 40 items (scoring range 40–200), where a score of 70 serves as the threshold for a 40% benchmark disability. Scores of 70–106 signify “Mild autism” (40%–60% disability), 107–153 signify “Moderate autism” (70%–90% disability), and scores above 153 represent “Severe autism” (100% disability) as per RPwD Act 2016 guidelines. The scale evaluates autism symptom severity across six domains: social relationship and reciprocity, emotional responsiveness, speech-language and communication, behavior patterns, sensory aspects, and cognitive components.
The WHODAS 2.0 offers multiple configurations (12, 36, and 12+24 items). This study employed the 36-item proxy-administered version, appropriate for participants with significant communication or cognitive challenges. WHODAS 2.0 scores are standardized from 0 to 100, with higher values reflecting greater functional disability. 16 It assesses functioning across six domains: cognition, mobility, self-care, getting along, life activities, and participation in society. WHODAS 2.0 scores were calculated using the complex scoring method based on item response theory (IRT), as recommended by the WHO. Domain and total scores were transformed to a 0–100 scale.
Data Collection Procedure
After obtaining ethics approval and permissions from participating centers, participants were recruited from clinical and community settings, including outpatient clinics, a hospital-based psychiatric daycare program, and community-based rehabilitation centers. Written informed consent was obtained from participants and their caregivers. In cases where participants had written, verbal, or cognitive difficulties, assent was obtained from the participants, along with consent from parents or legal guardians. Sociodemographic details and information on co-occurring conditions were extracted from clinical records.
The ISAA was administered by the first author, a qualified psychiatrist with over 3 years of clinical experience following a postgraduate psychiatry qualification. Caregivers completed the proxy-administered WHODAS 2.0. The first author provided clarifications to caregivers when required to facilitate an accurate understanding of the WHODAS 2.0 items.
Analysis
The data were analyzed using IBM SPSS version 24 for descriptive and inferential statistics. 17 Correlational analysis was carried out using Spearman’s rank correlation coefficient on the WHODAS 2.0 and ISAA scores, given the non-normal distribution of scores. To further examine the relationship between autism symptom severity and functional disability, a linear regression analysis was performed with the WHODAS 2.0 total score as the dependent variable and the ISAA total score as the primary independent variable. Intellectual disability (coded as a binary variable: present/absent) and age (in years) were included as covariates to adjust for their potential influence on functional disability. Statistical significance was set at p < .05.
Results
Table 1 presents the demographic characteristics of the 78 participants included in the study. The mean age of participants was 24.05 years (SD = 5.41), with most participants aged 18–25 (70.5%). The sample was predominantly male (87.2%). Participants were recruited from community-based rehabilitation centers (38.46%), followed by outpatient clinics (30.76%), hospital-based Psychiatric daycare program (15.38%), and inpatient wards (14.10%).
Demographic Characteristics of Participants (N = 78).
IDD: Intellectual and Developmental Disabilities, ADHD: Attention-deficit hyperactivity disorder.
Comorbid conditions were common and identified from available clinical records. Intellectual and developmental disability (IDD) was present in 69.7% of participants, and 29.5% had co-occurring mental illness. ADHD was noted in around 18.0%, and other medical conditions in 23.1%. Overall, 85.9% of participants had one or more comorbid conditions, while 14.1% had autism without additional diagnoses.
ISAA scores were not normally distributed, whereas WHODAS 2.0 scores were normally distributed. The mean (M) total WHODAS 2.0 score was 35.69 (SD = 15.44). Domain-wise analysis revealed that the highest mean scores were in getting along with people (M = 54.74, SD = 23.30) and understanding and communication (M = 50.69, SD = 23.50), suggesting greater challenges in social and communicative domains. Higher scores were also observed in participation in society (M = 41.99, SD = 20.51) and in life activities (M = 40.99, SD = 22.64). Lower scores were recorded for self-care (M = 24.84, SD = 18.65), and the lowest mean score was in the domain of getting around (M = 1.09, SD = 6.58) (Refer to Supplementary Table S1)
The median (Mdn) ISAA score was 90.50 (IQR = 39). The highest median score was in “social relationship and reciprocity” (Mdn = 30.0, IQR = 13), while the lowest was in the “cognitive component” domain (Mdn = 7.0, IQR = 4). The median scores for the other ISAA domains were as follows: speech, language, and communication (Mdn = 17.5, IQR = 8); behavior patterns (Mdn = 13.0, IQR = 8); and emotional responsiveness and sensory aspects (Mdn = 10.0, IQR = 5) (Refer to Supplementary Table S2)
Mean WHODAS scores increased progressively across ISAA-defined severity groups, as shown in Table 2. Participants scoring below the ISAA cutoff of 70 (n = 22) had a mean WHODAS score of 19.22 (SD = 8.74). Those in the mild group (n = 36) had a mean score of 36.53 (SD = 10.74). The moderate group (n = 20) had the highest mean WHODAS score (52.29; SD = 8.03). A one-way ANOVA confirmed significant differences in mean WHODAS scores across groups (p < .001), indicating increasing functional disability with greater symptom severity. None of the participants in this group met the criteria for severe autism based on ISAA scores.
Comparison of WHODAS 2.0 Scores Across ISAA Severity Categories.
ISAA: Indian Scale for Assessment of Autism, WHODAS 2.0: World Health Organization Disability Assessment Schedule 2.0.
Spearman’s rank correlation analysis demonstrated a strong positive association between ISAA total scores and WHODAS 2.0 total scores (ρ = 0.83, p < .001) (Figure 1). All ISAA domain scores showed significant positive correlations with WHODAS total scores, with stronger associations observed in the social reciprocity, emotional responsiveness, communication, and behavioral domains (Table 3).
ISAA: Indian Scale for Assessment of Autism, WHODAS 2.0: World Health Organization Disability Assessment Schedule 2.0.
Correlation Between ISAA Domain Scores and WHODAS 2.0 Total Score.
ISAA: Indian Scale for Assessment of Autism, WHODAS 2.0: World Health Organization Disability Assessment Schedule 2.0.
Multivariable linear regression analysis was conducted with the WHODAS 2.0 total score as the dependent variable and the ISAA total score as the primary independent variable. IDD and age were included as covariates. ISAA total score remained a significant independent predictor of functional disability (B = 0.46, 95% CI: 0.36–0.57, p < .001). The presence of IDD was also independently associated with higher WHODAS scores (B = 6.55, 95% CI: 1.22–11.87, p = .017). Age showed a positive but non-significant association with WHODAS scores (B = 0.33, p = .075). The model explained 70.8% of the variance in WHODAS 2.0 scores (adjusted R2 = 0.696) (Table 4).
Multivariate Linear Regression Predicting Functional Disability (WHODAS 2.0 Total Score).
R2 Adjusted R2 = 0.696.
Discussion
This study examined the relationship between autism symptom severity and functional disability in adults with ASD, using two standardized tools: the ISAA and the WHODAS 2.0. A strong positive correlation (ρ = 0.828) was found between ISAA and WHODAS scores, showing that greater symptom severity was linked to higher levels of functional disability. Importantly, this association remained significant after adjusting for age and comorbid IDD, suggesting that autism symptom severity contributes independently to functional outcomes in adulthood. At the same time, the findings indicate that functional disability in adults with autism cannot be fully explained by symptom severity alone. Comorbid IDD was independently associated with higher disability scores, highlighting the additional impact on real-world functioning.
Although symptom severity and IDD together accounted for a substantial proportion (R2 = 0.696) of variance in functional disability, a meaningful amount of variability (around 30%) remained unexplained. This residual variance is likely to reflect aspects of adult functioning that are not captured by symptom-based measures. These findings are consistent with existing literature indicating that a range of personal and contextual factors beyond core symptom severity influence functional outcomes in adults with autism.18–20 Personal factors, such as difficulties with executive functioning, cognitive flexibility, pragmatic communication, social judgment, and adaptation to complex or unstructured daily demands, are commonly reported in adulthood and may substantially influence day-to-day functioning. In addition, contextual factors such as family support, educational and vocational opportunities, access to services, and broader societal awareness are likely to shape participation and functional outcomes. 21 In the present sample, competitive employment was uncommon despite higher educational attainment in some participants, with most individuals engaged in sheltered or semi-structured vocational settings, highlighting ongoing challenges in adult role functioning. 22 Rather than representing a limitation of the model, this unexplained variance highlights the multidimensional nature of disability in adults with autism. It reinforces the distinction between symptom severity and real-world functioning.
A notable finding in our study was that nearly one-third of participants (n = 22) with a confirmed clinical diagnosis of autism and/or presence of UDID card and active engagement with disability-related services did not meet established symptom-based thresholds (ISAA score of 70) when assessed in adulthood. This observation warrants particular attention, as it raises important questions regarding the relationship between symptom severity and functional disability across the lifespan. First, longitudinal studies suggest that certain observable autism symptoms, particularly those related to overt social and behavioral features, may attenuate with age, even as functional challenges related to independent living, employment, meaningful reciprocal relationships, and community participation often persist or newly emerge in adulthood.23,24 Second, adults with autism may develop compensatory or masking strategies that reduce the outward expression of symptoms, particularly in structured or familiar environments, thereby influencing symptom-based assessments. 25 Consequently, individuals with even milder symptom presentations may continue to experience meaningful functional limitations that are not fully reflected in symptom severity scores and may face persistent challenges in social and community integration, as noted in prior research. 26 Third, this finding may reflect a limitation of the ISAA itself, which was adapted from a child-focused instrument and has not been formally validated in adult populations. As such, it may not fully capture adult-relevant manifestations of autism, particularly those related to complex social roles, independence, and community participation. 24 From a clinical and policy perspective, this has important implications. Reliance on symptom-based thresholds alone may risk under-identifying adults who experience meaningful functional impairments but do not meet established severity cut-offs.
The male predominance observed in this sample, consistent with global diagnostic trends, is another notable finding. 27 Females may present with subtler or camouflaged symptoms or face sociocultural barriers to service access, as noted in the literature.28,29 Although given the nature of the sampling, this may not reflect broader gender patterns, it highlights the need for assessment approaches that move beyond symptom-based evaluation and are sensitive to gender differences.
Domain-wise, the WHODAS 2.0 analysis revealed that “getting along with people” and “understanding and communication” were the most affected domains, aligning with the core social-communicative challenges of ASD that often persist into adulthood.25,30 Higher scores in “participation in society” and “life activities” further highlight difficulties in community integration and independent functioning. Conversely, lower scores in “self-care” and “getting around” suggest relatively preserved mobility and basic daily living skills in many persons with ASD, reflecting the heterogeneity of adult functioning profiles.1,31 Prior research indicates that with structured supports, adults with autism can acquire essential self-care skills, even in the presence of enduring social limitations. 32
ISAA domains related to social relationships and reciprocity, emotional responsiveness, and communication demonstrated stronger correlations with WHODAS 2.0 scores, consistent with earlier findings that social and communication challenges often persist into adulthood and predict lower independence, social participation, and quality of life.25,30,33 Conversely, ISAA domains assessing sensory aspects and cognitive components showed weaker correlations with functional disability. This may reflect that traits such as unusual memory, visual strengths, savant abilities, or even unusual sensory perceptions, though diagnostically salient, do not always translate into impaired functioning; in some cases, they may serve as relative strengths or adaptive mechanisms, particularly when leveraged in supportive vocational or educational settings.34–37 Emerging evidence suggests that some autism-related features, such as sensory sensitivities or behavioral disturbances, may lessen with age due to neurodevelopmental changes or improved coping strategies.33,38 Therefore, disability assessments that focus narrowly on symptoms such as using ISAA may overlook such strengths. 39
To the best of our knowledge, this study is among the first to systematically examine the association between autism symptom severity and functional disability in an adult ASD population using standardized, validated tools. The focus on adults with autism addresses a population that remains underrepresented in both research and disability assessment literature, particularly in low- and middle-income countries. The domain-wise analysis of ISAA and WHODAS 2.0 allows for a more nuanced understanding of how specific symptom profiles relate to functional outcomes. Including participants across multiple clinical and community-based service settings also enhances the ecological validity of the results.
Limitations
This study also has several limitations. Independent confirmation of ASD diagnosis was not carried out using any structured research instrument, but relied solely on clinical interview. The sample is from a tertiary care and other service-engaged population, which may limit generalizability to community-based adults who may not be accessing services. A relatively young-adult sample limits conclusions about disability in mid and later adulthood. The absence of participants in the severe autism range limits conclusions across the full severity spectrum. Although proxy-rated WHODAS 2.0 was appropriate for participants with communication or cognitive challenges, it may not fully reflect subjective experiences of disability. Caregivers may overestimate or underestimate disability due to burden or distress, adaptation over time, relationship dynamics, expectancy biases, or limited awareness of functioning across contexts. Such biases may influence reported disability levels. Finally, while age and intellectual disability were adjusted for, other factors—such as psychiatric comorbidities, adaptive functioning, environmental supports, and socioeconomic context—were not included in multivariable models and may account for the residual variance observed.
Future Directions
Future studies should include larger and more diverse samples, with greater representation of females and community-dwelling adults, to improve generalizability. Broader measures of adult functioning, such as adaptive behavior, executive functioning, mental health comorbidities, environmental support, and interpersonal relationships, may help clarify contributors to functional disability beyond symptom severity. The use of self-reported WHODAS 2.0 in cognitively able adults could provide additional insights into the lived experiences of disability.
Conclusion
This study demonstrates a strong association between autism symptom severity and functional disability in adults, while also showing that symptom severity alone does not fully explain real-world functional outcomes. Even after accounting for comorbid intellectual disability, a meaningful proportion of functional variability remained unexplained, pointing to the role of additional adult-specific functional and contextual factors. These findings highlight the multidimensional nature of disability in adulthood. While further research is warranted, these preliminary insights support a more inclusive, function-focused approach to more accurate disability evaluation and service planning in adults with ASD.
Supplemental Material
Supplemental material for this article is available online.
Supplemental Material
Supplemental material for this article is available online.
Footnotes
Acknowledgements
None.
Reporting Guideline (Supplementary Online)
Name: STROBE
Citation: von Elm E, Altman DG, Egger M, et al. The Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) statement: Guidelines for reporting observational studies. Ann Intern Med 2007; 147(8): 573–577.
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Declaration Regarding the Use of Generative AI
No part of this article was written or generated by a generative AI tool. The authors take full responsibility for the accuracy, integrity, and originality of the published article.
Ethical Approval
This study was approved by the Institutional Ethics Committee of the National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, India.
Name of the Institutional Ethics Committee/ Independent Review Board: National Institute of Mental Health and Neurosciences (NIMHANS), Bengaluru, India.
Approval Ref. No: NIMH/DO/BEH. Sc. Div./ 2023-24.
Date: November 10, 2023.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Informed Consent
Informed consent was obtained from all participants. For participants with communication difficulties, assent was obtained alongside parent or guardian consent.
Registration
Trial registry name: NA.
URL: NA.
Registration number: NA.
Citation Diversity Statement
We are committed to equitable citation practices and have made conscious efforts to include work from authors of diverse genders, geographic regions (including the Global South), career stages, and historically marginalized groups. We aim to support a more inclusive and representative scholarly record.
References
Supplementary Material
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