Autism spectrum disorder: Keys to early detection and accurate diagnosis
Careful attention is required for early detection and to rule out other conditions
Characteristics of ASD
Table 16,8,10,13,15,26-29 outlines various characteristics of ASD, which may manifest in varying degrees among children with the condition.
Speech/language. Speech helps to facilitate bonding between parents and an infant by offering a soothing, pleasurable, and reinforcing experience.30 More than 50% of children with ASD have language delays or deficits that persist throughout adulthood.13 The extent of these language deficits varies; in general, the more severe the speech/language deficits, the more severe the long-term symptoms.13 Language deficits in young children with ASD tend to be of both the expressive and receptive type, with onset in infancy, which suggests that neural processes predate the emergence of behavioral symptoms of ASD, and also that early language deficits/delays could be a marker for or indicator of future risk of ASD.13 Individuals with ASD also have been noted to have limitations in orienting or attending to human voices.13,30
Facial recognition. Evidence has linked ASD with deficits in facial recognition that emerge in the first few months of life.2 Earlier studies have found that lack of attention to others’ faces was the strongest distinguishing factor between 1-year-olds with ASD and typically developing 1-year-olds.2,31 A recent study that used EEG to compare facial emotion recognition in boys with ASD vs typically developing boys found that boys with ASD exhibited significantly lower sensitivity to angry and fearful faces.27
Other features. A 2020 study (N = 37) found that compared with typically developing children, those with ASD show less “interactional synchrony’’ (a dynamic process in which the timing of children and caregivers’ behaviors [specifically, vocalizations and movements] become mutually coordinated) with both familiar and unfamiliar adults.32 These researchers concluded that impairment in interactional synchrony may be linked to social communication deficits in ASD.32
A recent study (N = 98) evaluated “sluggish cognitive tempo” in 3 groups of children: children with attention-deficit/hyperactivity disorder (ADHD), children with ASD, and children with both ADHD and ASD.33 It found that children with ASD exhibited sluggish cognitive tempo at levels similar to those of the other 2 groups, and indicated that sluggish cognitive tempo may be linked with “social and global impairment above and beyond” the impairment associated with ASD.
Understanding early aberrations in neurobiologic processes in ASD can help develop biomarkers for early recognition of ASD, as well as guide the development of targeted interventions and treatments (Box1-3,7-9,12,13,30,35-39).
Box
Compared with individuals who do not have autism spectrum disorder (ASD), individuals with ASD exhibit anatomical differences in the brain that can be seen on MRI.9,35 Brain regions affected in ASD include the frontal gyrus, temporal gyrus, cingulate gyrus, postcentral gyrus, precuneus, caudate, and hippocampus.9 Some studies have found anomalous structural neural characteristics in infants, such as in the uncinate fasciculus, that correlated with later joint attention challenges, while others have found aberrations in the corpus callosum(responsible for transfer of procedural learning between the hemispheres, and oculomotor response)and internal capsule (responsible for sensorimotor function, as well as other functions) in children with ASD.12
Widespread white matter anomalies have been noted in ASD.12,35,36 In a 2-year longitudinal study that used diffusion tensor imaging, Li et al35 found that preschool children with ASD experience overgrowth of the uncinate fasciculus, which is one of the brain regions implicated in socioemotional processing, and concluded that this overgrowth correlated with ASD severity.35 Andrews et al37 used diffusion-weighted MRI to examine white matter in 127 preschool children. They found that compared with typically developing children, children with ASD exhibited altered white matter microstructure.37
Research suggests that developing representations of the reward value of social stimuli may be challenging for children with ASD.2 Abrams et al30 used resting-state functional brain MRI to evaluate children with typical development and children with highfunctioning, “verbally fluent” ASD. They found that the children with ASD exhibited lower functional connectivity between voice-specific left hemisphere posterior superior temporal sulcus and areas representing the reward circuitry.30 This study also found that children with ASD had underconnectivity between the right hemisphere posterior superior temporal sulcus (which deals with speech prosody) and areas known for emotion-linked associative learning, the orbitofrontal cortex and amygdala.30 These findings are thought to align with the social motivation theory of ASD.13,30,38
The extent of underconnectivity between these systems was found to determine the severity of communication challenges in high-functioning children with ASD.30 One MRI study observed lower gray matter volume in the voice-selective bilateral superior temporal sulcus in children age approximately 9 to 11 years with ASD.39
Neural systems responsible for facial recognition (particularly the right fusiform gyrus and other brain areas) have been shown to exist or begin “very early in life,” which suggests that impaired face recognition may be an early marker of ASD.2 In addition to problems with visual scanning, preferential attention to (and visual sensitivity to) biological motion is a forerunner for the development of social interactions in infants, specifically in regard to being able to detect and recognize emotion, which is considered vital for attachment.7,8 Impaired biological motion perception has been found in very young children with ASD.7,8 This presents an important avenue/potential biomarker for further research to better understand neurobiologic processes underlying atypical development at an earlier age.3,8
Early neural biomarkers for ASD
Nonlinear EEG values may serve as an early neurobiomarker for detecting ASD in young children.1 Because it is relatively inexpensive and convenient, EEG may be highly useful for detecting ASD.1 A study that compared EEG results of 99 infants who had siblings with ASD and 89 low-risk controls from age 3 months to 36 months found that nonlinear EEG measurements predicted with high accuracy later diagnosis of ASD, and were strongly correlated with later Autism Diagnostic Observation Schedule scores.1
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