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Summary: Some children diagnosed with Autism Spectrum Disorders (ASDs) may have a low mental age, which means they function cognitively below the level of a 12-month-old. Our study focused on the diagnosis, symptom severity, and progress of children with ASD-Low MA, Autistic Disorder according to DSM-IV-TR, and PDD-NOS according to DSM-IV-TR at the age of two and during a follow-up at age four. The findings revealed that most children with ASD-Low MA continued to show signs of ASD at the follow-up, displaying slow developmental progress and more severe symptoms.
Key terms: autism spectrum disorders, low mental age, developmental advancement, diagnostic consistency, severity of autism
ASDs are characterized by difficulties in social interaction, communication, and the presence of repetitive behaviors and restricted interests. The spectrum includes conditions such as Autistic Disorder (AD), PDD-NOS, and Asperger’s Disorder.
Early detection and intervention are essential in improving the outcomes for children with ASDs. Screening tools like the Checklist for Autism in Toddlers and Screening Tool for Autism in Two-Year-Olds can aid in early ASD diagnosis.
The accuracy of assessing IQ in children with ASDs has been debated, but studies have shown consistent nonverbal intelligence levels in these children. Validation of diagnostic protocols for autism in children with low mental age is crucial.
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For this study, data collection relied on the DSM-IV-TR criteria for diagnosing AD and PDD-NOS. Children with ASD-Low MA displayed significant ASD symptoms during the follow-up, indicating the importance of diagnosing ASDs in children with a low mental age. The group with AD was expected to show the most stable diagnosis.
Expectations included limited developmental progress in children with ASD-Low MA, a lower percentage of children remaining on the autism spectrum, and more severe autism symptoms in the AD group.
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The study involved 219 children aged between 16 and 30 months, diagnosed with an ASD at age two and monitored until age four. Analysis of demographic data revealed no notable variations between groups concerning gender, ethnicity, or income.
Demographic Overview
The demographic details are displayed in Table 1. The average age of children in the ASD-Low MA group at Time 1 was approximately 2.5 months younger than the other groups. Males were more prevalent, consistent with data on autism prevalence.
Table 1.
Participant Demographics Based on Group
| AD Age: M (SD) Range |
PDD-NOS Age: M (SD) Range |
ASD-Low MA Age: M (SD) Range |
Difference Between Groups |
||
|---|---|---|---|---|---|
| Time 1 | 27.09 (4.57) | 25.88 (4.04) | 23.60 (4.509) | F (4, 428) = 3.67, p < .006 | |
| 17.74 – 36.66 | 18.03 – 34.43 | 15.70 – 31.80 | |||
| Time 2 | 53.27 (9.41) | 51.49 (10.38) | 49.37 (6.48) | ||
| 41.38 – 113.48 | 38.12 – 106.52 | 34.36 – 62.13 | |||
| AD Frequency (%) | PDD-NOS Frequency (%) | ASD-Low MA Frequency (%) | Difference Between Groups | ||
| Gender | |||||
| Male | 93(83.8%) | 65 (78.3%) | 20 (80%) | X 2 (2, N = 219) = .964, p = .617 | |
| Female | 18 (16.2%) | 18 (21.7%) | 5 (20%) | ||
| Total | 111 | 83 | 25 | ||
| Ethnicity | |||||
| White | 87(82.1%) | 67(84.8%) | 19(76%) | X 2 (8, N = 210) = 7.450, p = .490 | |
| Black | 2(1.9%) | 4(5.1%) | 2(8%) | ||
| Hispanic/Latino | 9(8.5%) | 5(6.3%) | 3(12%) | ||
| Asian | 4(3.8%) | 3(3.8%) | 0 | ||
| Biracial | 4(3.8%) | 0 | 1(4%) | ||
| Total | 106 | 79 | 25 | ||
| Maternal Education | |||||
| No degree | 3 (4.3%) | 2 (3.1%) | 0 | X 2 (12, N = 154) = 9.675, p = .645 | |
| High school diploma/GED | 22 (31.4%) | 20 (30.8%) | 11 (57.9%) | ||
| Vocational/technical degree | 5 (7.1%) | 5 (7.7%) | 0 | ||
| Associate’s degree | 6 (8.6%) | 6 (9.2%) | 0 | ||
| Bachelor’s degree | 20 (28.6%) | 19 (29.2%) | 4 (21.1%) | ||
| Master’s degree | 11(15.7%) | 12(18.5%) | 4 (21.1%) | ||
| Doctoral degree | 3(4.3%) | 1(1.5%) | 0 | ||
| Total | 70 | 65 | 19 | ||
| Annual Income | |||||
| $0–$10,000 | 6 (9.5%) | 1(1.6%) | 0 | X 2 (20, N = 143) = 23.166, p = .281 | |
| $10,000–$20,000 | 10 (15.9%) | 13(20.6%) | 2 (11.8%) | ||
| $20,000–$30,000 | 4 (6.3%) | 3(4.8%) | 0 | ||
| $30,000–$40,000 | 3(4.8%) | 5(7.9%) | 4 (23.5%) | ||
| $40,000–$50,000 | 6 (9.5%) | 7(11.1%) | 2 (11.8%) | ||
| $50,000–$60,000 | 4(6.3%) | 6(9.5%) | 2 (11.8%) | ||
| $60,000–$70,000 | 6(9.5%) | 6(9.5%) | 0 | ||
| $70,000–$80,000 | 7(11.1%) | 7(11.1%) | 3(17.6%) | |
| $80,000–$90,000 | 7(11.1%) | 3(4.8%) | 2 (11.8%) | |
| $90,000–$100,000 | 5(7.9%) | 2(3.2%) | 2(11.8%) | |
| >$100,000 | 5 (7.9%) | 10(15.9%) | 0 | |
| Total | 63 | 63 | 17 | |
Please note that the age is indicated in months.
Evaluation criteria
The study utilized DSM-IV-TR criteria for diagnosing Autism Disorder (AD) and Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS). In order to be included in the study, children had to have at least one age equivalent score at or above 12 months on the Mullen Scales of Early Learning (MSEL) Visual Reception, Receptive Language, or Expressive Language scales.
Children were categorized as having ASD-Low MA if they exhibited at least one symptom from the social cluster, one symptom from the communication cluster, and/or one symptom in the RRBs cluster. Furthermore, their age equivalent scores on the MSEL scales and the Vineland Adaptive Behavior Scales (VABS) Communication and Socialization domains had to be below 12 months (refer to Table 2).
Table 2.
Mean (SD) Age Equivalent Scores by Group
| Autism Spectrum Disorder | Pervasive Developmental Disorder-Not Otherwise Specified | Autism Spectrum Disorder with Low Mental Age | ||||
|---|---|---|---|---|---|---|
| First Time | Second Time |
|---|---|
| Time Slot 1 | Time Slot 2 |
| Time Frame 1 | Time Frame 2 |
| MSEL Visual Reception | |||||
| Mean: 18.05 (SD: 5.37) | Mean: 37.67 (SD: 15.97) | Mean: 18.81 (SD: 4.51) | Mean: 42.67 (SD: 15.03) | Mean: 8.75 (SD: 2.05) | Mean: 19.83 (SD: 8.11) |
| n = 80 |
| n = 66 |
| n = 19 |
Disclaimer: Age equivalents are expressed in terms of months. The abbreviation “Ns” denotes the number of individuals with available data at both assessment points. The MSEL refers to the Mullen Scales of Early Learning, while the VABS stands for the Vineland Adaptive Behavior Scales.
At the initial assessment (Time 1), 111 children were diagnosed with Autism Spectrum Disorder (AD), 83 with Pervasive Developmental Disorder-Not Otherwise Specified (PDD-NOS), and 25 with ASD-Low Mental Age. In order to explore differences among these groups at follow-up, participants were categorized into six groups according to their diagnosis at Time 2.
## Screening Procedures
Participants underwent screening using either the M-CHAT or M-CHAT-R at their healthcare provider or through early intervention services between 16 and 30 months of age. Those who screened positive received a complimentary developmental and diagnostic assessment from qualified professionals. Assessments were mainly conducted at the university clinic, with transport assistance provided when needed. Diagnoses were determined based on various assessments including observation, developmental history, and test results.
Children qualified for a follow-up evaluation at 42 months of age or older, utilizing the same measures and diagnostic criteria as the initial assessment.
## Mullen Scales of Early Learning (MSEL)
The MSEL is a standardized test measuring cognitive abilities in children up to 68 months of age. This study focused on the Visual Reception, Fine Motor, Expressive Language, and Receptive Language scales. Age equivalents and developmental quotients were computed based on previous studies involving children with low mental capacities.
Tables displayed mean Developmental Quotient Scores per group for categories like Visual Reception, Fine Motor, Receptive Language, Expressive Language, Interpersonal Relationships, Play and Leisure, and Coping at different time points.
To gauge development between assessments, the age equivalent scores for each MSEL scale were compared. The difference reflected the cognitive growth over time, with the ratio between evaluations determining the rate of progress. A ratio exceeding 1 indicated faster-than-expected progress, 1 showed expected progress, and less than 1 signified slower advancement. This value, known as the Learning Rate or Intervention Efficiency Index, enabled comparisons of developmental progress across different time periods or children with similar mental ages.
### Vineland Adaptive Behavior Scales, Interview Edition (VABS)
The VABS is a standardized parent questionnaire assessing a child’s adaptive skills in Communication, Daily Living, Socialization, and Motor Skills. It boasts strong reliability and validity, widely used across clinical settings. For the age range studied, the VABS demonstrated high internal consistency and reliability.
Age equivalents are detailed in Table 2. Similar methodologies employed for MSEL scales were applied to VABS Socialization and Communication domains for tracking growth between assessments (refer to Tables 3 and 4).
### Autism Diagnostic Observation Schedule – Generic (ADOS)
The ADOS is a structured evaluation focusing on ASD symptoms observed during testing. The study utilized Modules 1 and 2, with all children meeting the autism spectrum threshold.
### Childhood Autism Rating Scale (CARS)
The CARS is a rating scale that assesses ASD-related behaviors, indicating symptom severity levels ranging from non-autistic to severe.
## Statistical Analysis
ANOVA was utilized to identify differences in DQs between groups at each time point and regarding developmental gains overall. Power analysis confirmed adequate power to detect small to medium effects.
The study examined diagnostic stability across groups, comparing diagnostic outcomes and ASD versus non-ASD diagnoses using Chi square tests.
In the early stages of the investigation, participants were classified into distinct diagnostic categories at two different time points, with diagnostic frequencies and percentages tabulated.
**Table 1: Diagnostic Outcomes at Time 1 and Time 2** illustrates the distribution of diagnoses at both Time 1 and Time 2.
**Table 2: ASD vs Non-ASD Diagnostic Outcomes at Time 2** details diagnostic outcomes for ASD versus non-ASD groups at Time 2.
**Table 3: ASD Severity on CARS by Group** shows ASD severity based on CARS scores among different diagnostic groups.
Additionally, a mixed-model ANOVA delved into the connection between initial diagnosis and autism symptom severity over time, outlined in **Table 4: Summary of Mixed-Model ANOVA Results**.
Attrition rates were analyzed, revealing factors such as ethnicity and gender influencing participant return for follow-up evaluations, detailed in **Table 5: Summary of Attrition Data**.
Data on Time 1 variables returned at Time 2 included Age, CARS Total Score, and MSEL Visual Reception DQ, with statistical differences noted. Gender distribution indicated a significant difference between male and female participants. Ethnicity breakdown demonstrated variations across ethnic groups. Diagnoses were also reported, with notable differences among groups.
Furthermore, Age equivalents, DQs, and ASD-Low MA group performance were detailed in Tables 2 and 3, indicating lower cognitive and adaptive functioning in the ASD-Low MA cohort. Developmental growth rates shown in Table 4 suggested smaller gains in the ASD-Low MA group compared to AD or PDD-NOS.
Post-hoc assessments highlighted significant differences in progress among groups in various domains. The ASD-Low MA group consistently exhibited slower progress compared to AD or PDD-NOS. VABS Daily Living data, not included, displayed consistent patterns. Hypotheses regarding diagnostic stability and autism symptom severity were tested, revealing distinct outcomes among groups.
In summary, the study aimed to analyze developmental growth, diagnostic stability, and autism symptom severity over a two-year span in children diagnosed with AD, PDD-NOS, and ASD-Low MA initially. The ASD-Low MA group displayed slower progress and severe autism symptoms compared to other groups, affirming the validity of early autism diagnoses in children with cognitive impairments.
Our initial expectation was that individuals in the AD group would display the most pronounced symptoms of ASD at both assessment points, with the slowest rates of symptom improvement compared to the PDD-NOS and ASD-Low MA groups. Surprisingly, we observed that the AD group actually showed the most progress in reducing autism symptom severity, despite their average scores still falling within the autistic spectrum. Meanwhile, the PDD-NOS group demonstrated less improvement than the AD group, and the ASD-Low MA group exhibited the most severe symptoms initially and minimal improvement over time. These findings partly supported our hypotheses and underscored the accuracy of ASD diagnosis in children with low cognitive abilities.
The results imply that ASDs can be reliably identified even when children have low mental age. Symptoms of autism remain severe and stable in this subgroup, reinforcing the validity of diagnosing individuals with an autism spectrum disorder regardless of their cognitive abilities. A large number of children in the AD and PDD-NOS categories were diagnosed with autism upon follow-up. The removal of the PDD-NOS classification and the inclusion of restricted and repetitive behaviors (RRBs) in DSM-5 may result in some children not meeting the criteria for an ASD diagnosis and consequently missing out on important interventions.
The AD group experienced greater symptom improvement thanks to early interventions, although there were no notable differences in cognitive or adaptive progress compared to the PDD-NOS group. The ASD-Low MA group displayed significant disparities in functional abilities and growth rates relative to the other two autism subgroups. Study limitations include sample size, attrition bias, timeframe constraints, and a lack of evaluation on the impact of interventions. Further research is necessary to confirm the accuracy of ASD diagnoses in children with low cognitive abilities, and longitudinal studies should monitor these individuals well into adolescence to evaluate their developmental trajectories.
| Understanding Autism | ||
| _______ | For a child to be diagnosed, symptoms should be present in Clusters 1, 2, and 3 | |
| ALSO | ||
| _______ | A child needs to exhibit at least SIX OR MORE symptoms in total | |
| ALSO | ||
| ________ | The child must demonstrate signs of ASD before reaching the age of three | |
| ALSO | ||
| Requirements | |
| Children must be at least 12 months old | |
| ________ | |
| Satisfies requirements for a disorder or condition not recognized by DSM-IV-TR | |
Footnotes
Adherence to Ethical Guidelines
Approval of Ethics
We ensured that all activities involving human subjects adhered to the ethical principles.
Consent of Participants
Prior consent was obtained from each participant before their involvement in the study.