Introduction
Autism Spectrum Disorder (ASD) is a developmental disorder that affects social communication and behavior. One of the factors that influences the diagnosis and outcome of ASD is intelligence quotient (IQ), which measures cognitive abilities. However, the relationship between IQ and ASD is complex and varies depending on the age and subtype of autism. In this perspective, the author reviews the neurobiological and genetic evidence that may explain the co-occurrence of ASD and low IQ, as well as the possibility that high IQ may protect against some of the social impairments of ASD. The author also proposes a novel maturational framework that distinguishes different subtypes of ASD based on the timing and severity of IQ impairments.
Early low IQ and ASD
About 37% of 8-year-old children and 48% of 4-year-old children diagnosed with ASD also have Intellectual Disability (ID), with IQ below 70. Moreover, low IQ in early infancy, including 1 year of age, carries a 40% greater chance of receiving ASD diagnosis in early childhood. The author suggests that early low IQ may subsume a subgroup of individuals with ASD, in particular, those diagnosed with autism in very early childhood. This subtype of ASD may have a different etiology and neurobiology from later-diagnosed, average or higher-IQ cases, and from children with speech delay onset. The author provides evidence from brain imaging, genetics, and epigenetics to support this hypothesis.
Brain imaging evidence
Studies have shown that children with ASD and low IQ have atypical brain overgrowth during the first and second year of life, especially in the cerebellar, cerebral, and limbic structures. These areas are responsible for higher-order cognitive, emotional, social, and language functions. The author argues that this brain overgrowth may reflect a disruption of critical periods of brain development, which are windows of opportunity for learning and plasticity. The author also suggests that early low IQ may be a marker of abnormal brain maturation, rather than a static trait.
Genetic and epigenetic evidence
Studies have also shown that children with ASD and low IQ have more de novo mutations, which are new mutations that arise in the child and are not inherited from the parents. These mutations tend to affect genes that are involved in synaptic function, neuronal migration, and chromatin remodeling. The author proposes that these mutations may impair the formation and pruning of neural connections, leading to abnormal brain development and function. The author also discusses the role of epigenetics, which are changes in gene expression that are influenced by environmental factors. The author suggests that epigenetic factors may modulate the effects of genetic mutations and contribute to the variability and heterogeneity of ASD.
High IQ and ASD
On the other hand, some individuals with ASD have average or above-average IQ, and some even show exceptional abilities in certain domains, such as memory, mathematics, or music. The author considers the evidence that high IQ may protect against some of the social communication impairments of ASD, or that high IQ may reflect a different subtype of ASD with a different neurobiology and genetics. The author also explores the possibility that high IQ may be a result of compensatory mechanisms or enhanced learning in individuals with ASD.
Conclusion
The author concludes that the relationship between IQ and ASD is complex and dynamic, and that it may vary depending on the age and subtype of autism. The author proposes a novel maturational framework that distinguishes different subtypes of ASD based on the timing and severity of IQ impairments. The author also identifies gaps in knowledge and directions for future work in this area, such as investigating the longitudinal trajectories of IQ and ASD, the interactions between genetic and environmental factors, and the implications for diagnosis and intervention. The author hopes that this perspective will serve as a helpful guide for the complex and growing investigation of cognitive abilities and ASD.
FAQ
What is the difference between early low IQ and speech delay onset in ASD?
Early low IQ is a marker of abnormal brain maturation that affects both verbal and non-verbal domains, and is associated with ASD diagnosis in very early childhood. Speech delay onset is a specific impairment in language development that occurs in preschool or school-aged children, and is not necessarily related to IQ or brain overgrowth.
What are the advantages of distinguishing different subtypes of ASD based on IQ impairments?
Distinguishing different subtypes of ASD based on IQ impairments can help to better understand the etiology, neurobiology, genetics, and epigenetics of ASD, as well as the variability and heterogeneity of the disorder. It can also help to identify the specific needs and strengths of each subtype, and to tailor the interventions to the critical periods of brain development.
How can IQ be measured in infants and toddlers with ASD?
IQ can be measured in infants and toddlers with ASD using standardized tests that assess cognitive, language, and motor skills, such as the Mullen Scales of Early Learning, the Bayley Scales of Infant and Toddler Development, or the Differential Ability Scales. These tests can provide an estimate of the developmental level and the potential for learning of young children with ASD.
How can brain imaging techniques help in the diagnosis and intervention of ASD and IQ?
Brain imaging techniques can help in the diagnosis and intervention of ASD and IQ by measuring the brain structure, function, and connectivity of individuals with ASD and different levels of IQ. Brain imaging can reveal the patterns of brain overgrowth, undergrowth, or atypical development that may be associated with ASD and IQ impairments. Brain imaging can also identify the brain regions and networks that are involved in cognitive, social, and emotional processes, and how they are affected by ASD and IQ. Brain imaging can also monitor the effects of interventions on brain development and function, and evaluate their efficacy and outcomes.
What are the critical periods of brain development and how are they disrupted in ASD?
Critical periods are windows of opportunity for learning and plasticity in the brain, during which specific experiences and stimuli are required for optimal neural development. They are disrupted in ASD by genetic and epigenetic factors that impair the formation and pruning of neural connections, leading to abnormal brain overgrowth and function.
How can genetic and epigenetic factors interact to influence the development of ASD and IQ?
Genetic and epigenetic factors can interact to influence the development of ASD and IQ by modulating the effects of genetic mutations, environmental exposures, and neural plasticity. For example, some genetic mutations may increase the risk of ASD and low IQ, but their effects may be mitigated by epigenetic factors that regulate gene expression. Conversely, some environmental factors may induce epigenetic changes that alter gene expression and affect brain development and function.
How can the maturational framework help in the diagnosis and intervention of ASD?
The maturational framework distinguishes different subtypes of ASD based on the timing and severity of IQ impairments, and provides a developmental perspective on the relationship between IQ and ASD. It can help in the diagnosis and intervention of ASD by identifying the specific needs and strengths of each subtype, and by tailoring the interventions to the critical periods of brain development.
What are some of the compensatory mechanisms or enhanced learning strategies that individuals with high IQ and ASD may use?
Some of the compensatory mechanisms or enhanced learning strategies that individuals with high IQ and ASD may use are: using cognitive empathy to infer others’ mental states, using verbal reasoning to solve social problems, using memory and attention to process social information, using logic and rules to guide social behavior, and using creativity and imagination to generate novel solutions.
What are some of the environmental factors that may influence the development of ASD and IQ?
Some of the environmental factors that may influence the development of ASD and IQ are prenatal and perinatal factors, such as maternal infection, inflammation, stress, nutrition, medication, and exposure to toxins or pollutants. These factors may affect the fetal brain development and the epigenetic regulation of gene expression. Other environmental factors are postnatal factors, such as social interaction, stimulation, education, and enrichment. These factors may affect the brain plasticity and the critical periods of learning and development.
What are some of the exceptional abilities that individuals with high IQ and ASD may show?
Some of the exceptional abilities that individuals with high IQ and ASD may show are savant skills, which are rare and remarkable talents in domains such as memory, mathematics, music, art, or calendar calculation. These skills may reflect an enhanced or specialized processing of specific types of information, such as patterns, numbers, or sounds.
What are some of the interventions that can optimize the outcomes and well-being of individuals with ASD and different levels of IQ?
Some of the interventions that can optimize the outcomes and well-being of individuals with ASD and different levels of IQ are early identification and diagnosis, individualized and evidence-based treatments, family and community support, educational and vocational opportunities, and social inclusion and acceptance. These interventions can help individuals with ASD and different levels of IQ to develop their cognitive, social, and emotional skills, and to achieve their full potential and quality of life.
Source:
https://acamh.onlinelibrary.wiley.com/doi/full/10.1002/jcv2.12214