Prevalence and Characteristics of Autism Spectrum Disorder in Individuals with Borderline Low IQ

Cognitive Distribution and Functional Impairment

Approximately 30% of individuals with Autism Spectrum Disorder (ASD) have co-occurring intellectual disability, with the cognitive profile in ASD ranging from severely impaired to superior ability 1, 2, 3
50% of ASD individuals have severe to profound intellectual disability (IQ typically <35-40) 4
35% of ASD individuals have mild to moderate intellectual disability (IQ typically 40-70) 4
15-20% of ASD individuals have IQ in the normal range (IQ ≥70) 4
Borderline intellectual functioning (IQ 70-85) represents a substantial portion of the ASD population, falling within or adjacent to the mild intellectual disability and normal range categories 4
Cognitive level is the primary driver of behavioral presentation variability in ASD, more so than the core social communication deficits themselves 1, 2, 3
Individuals with borderline low IQ and ASD show more pronounced functional impairment than those with average or above-average IQ 2, 3
Individuals with borderline low IQ and ASD face greater challenges with adaptive functioning despite having cognitive abilities in the borderline range 4
Approximately 90% of individuals with autism have at least one additional medical or mental health condition 1, 2, 3

Verbal skills are typically more impaired than nonverbal skills in classic autism presentations 4
Working memory and processing speed deficits are prominent and partially mediate IQ reductions 5
Receptive and expressive language test scores show decreased performance 5
Motor dysfunction is observed in early developmental course 5
The presence of borderline low IQ does not preclude ASD diagnosis but complicates the clinical picture 4
Comprehensive neurobehavioral evaluation should include efficient indicators of global ability, measures of sustained attention, working memory, and processing speed, assessment of receptive, expressive, and pragmatic language skills, evaluation of fine and gross motor skills, adaptive function assessment, and autism-specific measures 5

Individuals with ASD and borderline IQ face compounded functional challenges, with lifetime costs estimated at $2.4 million for ASD with intellectual disability compared to $1.4 million without 2, 3