Development of the pupillary light reflex from 9 to 24 months: association with common autism spectrum disorder (ASD) genetic liability and 3-year ASD diagnosis

Presymptomatic Biological, Structural, and Functional Diagnostic Biomarkers of Autism Spectrum Disorder

Autism spectrum disorder (ASD) is a common neurodevelopmental disorder clinically diagnosed by persistent deficits in three areas of social communication and interaction, plus at least two of four types of restricted repetitive behaviors. ASD has been shown to be caused by genetic predisposition and environmental factors; however, the heterogeneity of ASD complicates its diagnosis and treatment. Early behavioral interventions have shown significant benefits, emphasizing the urgent need for reliable diagnostic biomarkers to enhance long-term outcomes. Here we provide a systematic review that outlines current findings on genetic and neurological biomarkers for presymptomatic ASD diagnoses, assessed prior to the observation of behavioral manifestations. Specifically, we offer insights into the mechanisms of presymptomatic neurological, biological, structural, and functional markers for ASD, compare outcomes across studies, and critically assess their limitations and implications. Recent findings highlight genotype-guided therapeutic strategies in animal models, such as dietary zinc supplementation for reversing ASD-associated behaviors by synaptic deficits. However, the differential efficacy based on underlying genotypes, along with challenges in identifying reliable genomic biomarkers prior to symptom onset, indicates the need for further research. Notably, recent advancements in imaging technologies like magnetic resonance imaging, electroencephalography, and pupillometry have shown promising markers in neonates, and at 3 and 9 months old, respectively. Newer developments in magnetoencephalography hardware can facilitate the much-needed infant ASD studies. It is important to note that many of these biomarker findings are preliminary, and further validation for clinical use is required. Continued research is needed to advance the practicality, reliability, and acceptability of these biomarkers to improve ASD diagnosis and treatment strategies.

Sensory-movement underpinnings of lifelong neurodivergence: getting a grip on autism

While the autism diagnosis emphasizes "deficits" in social communication, the article advances that sensory-movement differences underpin autism through a review of the following sources of evidence. This account critically challenges "autistic regression", with evidence that sensory-movement features appear by birth as the earliest signs of autism and underlie the behavioral differences used for diagnosis, which may reflect adaptations to inherent differences and misunderstandings from others. Sensory and motor differences are salient to autistic people, but they often go underrecognized by others. They cause cascading effects in infancy on behavior and communication through differences in sensorimotor learning, automatic imitation, eye contact, sensory perception, and interests. The article then explains how sensory processing differences may influence reduced perceptual narrowing, which involves a bottom-up information processing style grounded in the surrounding environment. Furthermore, this bottom-up processing may grow from reduced sensory integration in feedback loops potentially involving the cerebellum of the brain. The article then moves into implications for the widespread consequences of these inherent differences on quality of life. The article closes with implications for autism as a construct (including underestimated empathy and pain), testing the theory, providing sensory-sensitive support and acceptance of autistic people, and applications to diverse autistic people. The theory may apply particularly well to autistic women and girls, autistic people with speech divergence, autistic people with ADHD, and autistic people with co-occurring sensory and motor-related neurodivergences. Throughout the article, the theory also provides clinical, neurological, and experiential evidence for sensory and motor differences as lifelong, challenging the notion of "losing" (an) autism (diagnosis) as instead reflecting (risky and not necessarily "successful") camouflaging.

Twenty-four-month effortful control predicts emerging autism characteristics

Longitudinal research can assess how diverging development of multiple cognitive skills during infancy, as well as familial background, are related to the emergence of neurodevelopmental conditions. Sensorimotor and effortful control difficulties are seen in infants later diagnosed with autism; this study explored the relationships between these skills and autism characteristics in 340 infants (240 with elevated familial autism likelihood) assessed at 4-7, 8-10, 12-15, 24, and 36 months. We tested: (1) the relationship between parent-reported effortful control (Rothbart's temperament questionnaires) and sensorimotor skills (Mullen Scales of Early Learning), using random intercept cross-lagged panel modelling; (2) whether household income and maternal education predicted stable individual differences in cognition; (3) sensorimotor and effortful control skills as individual and interactive predictors of parent-reported autism characteristics (Social Responsiveness Scale) at 3 years, using multiple regression; and (4) moderation of interactions by familial likelihood. Sensorimotor skills were longitudinally associated with effortful control at the subsequent measurement point from 12-15 months. Socioeconomic status indicators did not predict stable between-infant differences in sensorimotor or effortful control skills. Effortful control skills were longitudinally related to 3-year autism characteristics from the first year of life, with evidence for an interaction with sensorimotor skills at 24 months. Effects of effortful control increased with age and were particularly important for infants with family histories of autism. Results are discussed in relation to different theoretical frameworks: Developmental Cascades and Anterior Modifiers in the Emergence of Neurodevelopmental Disorders. We suggest a role for 24-month effortful control in explaining the emergent autism phenotype. RESEARCH HIGHLIGHTS: Sensorimotor skills longitudinally predicted effortful control from 12-15 months onward but effortful control did not longitudinally predict sensorimotor skills during infancy. Measures of effortful control skills taken before the age of 1 predicted continuous variation in autism characteristics at 36 months, with associations increasing in strength with age. Effortful control (measured at 12-15 and 24 months) was a stronger predictor of 36-month autism characteristics in infants with elevated familial likelihood for autism. The relationship between 24-month sensorimotor skills and 36-month autism characteristics was stronger in infants with weaker effortful control skills.

The potential and translational application of infant genetic research

In the current genomic revolution, the infancy life stage is the most neglected. Although clinical genetics recognizes the value of early identification in infancy of rare genetic causes of disorders and delay, common genetic variation is almost completely ignored in research on infant behavioral and neurodevelopmental traits. In this Perspective, we argue for a much-needed surge in research on common genetic variation influencing infant neurodevelopment and behavior, findings that would be relevant for all children. We now see convincing evidence from different research designs to suggest that developmental milestones, skills and behaviors of infants are heritable and thus are suitable candidates for gene-discovery research. We highlight the resources available to the field, including genotyped infant cohorts, and we outline, with recommendations, special considerations needed for infant data. Therefore, infant genetic research has the potential to impact basic science and to affect educational policy, public health and clinical practice.

Neonatal brain dynamic functional connectivity in term and preterm infants and its association with early childhood neurodevelopment

Brain dynamic functional connectivity characterises transient connections between brain regions. Features of brain dynamics have been linked to emotion and cognition in adult individuals, and atypical patterns have been associated with neurodevelopmental conditions such as autism. Although reliable functional brain networks have been consistently identified in neonates, little is known about the early development of dynamic functional connectivity. In this study we characterise dynamic functional connectivity with functional magnetic resonance imaging (fMRI) in the first few weeks of postnatal life in term-born (n = 324) and preterm-born (n = 66) individuals. We show that a dynamic landscape of brain connectivity is already established by the time of birth in the human brain, characterised by six transient states of neonatal functional connectivity with changing dynamics through the neonatal period. The pattern of dynamic connectivity is atypical in preterm-born infants, and associated with atypical social, sensory, and repetitive behaviours measured by the Quantitative Checklist for Autism in Toddlers (Q-CHAT) scores at 18 months of age.

Investigating the development of the autonomic nervous system in infancy through pupillometry

We aim to investigate early developmental trajectories of the autonomic nervous system (ANS) as indexed by the pupillary light reflex (PLR) in infants with (i.e. preterm birth, feeding difficulties, or siblings of children with autism spectrum disorder) and without (controls) increased likelihood for atypical ANS development. We used eye-tracking to capture the PLR in 216 infants in a longitudinal follow-up study spanning 5 to 24 months of age, and linear mixed models to investigate effects of age and group on three PLR parameters: baseline pupil diameter, latency to constriction and relative constriction amplitude. An increase with age was found in baseline pupil diameter (F(3,273.21) = 13.15, p < 0.001, [Formula: see text] = 0.13), latency to constriction (F(3,326.41) = 3.84, p = 0.010, [Formula: see text] = 0.03) and relative constriction amplitude(F(3,282.53) = 3.70, p = 0.012, [Formula: see text] = 0.04). Group differences were found for baseline pupil diameter (F(3,235.91) = 9.40, p < 0.001, [Formula: see text] = 0.11), with larger diameter in preterms and siblings than in controls, and for latency to constriction (F(3,237.10) = 3.48, p = 0.017, [Formula: see text] = 0.04), with preterms having a longer latency than controls. The results align with previous evidence, with development over time that could be explained by ANS maturation. To better understand the cause of the group differences, further research in a larger sample is necessary, combining pupillometry with other measures to further validate its value.

Infant temperamental fear, pupil dilation, and gaze aversion from smiling strangers

In childhood, higher levels of temperamental fear-an early-emerging proclivity to distress in the face of novelty-are associated with lower social responsivity and greater social anxiety. While the early emergence of temperamental fear in infancy is poorly understood, it is theorized to be driven by individual differences in reactivity and self-regulation to novel stimuli. The current study used eye tracking to capture infants' (N = 124) reactions to a video of a smiling stranger-a common social encounter-including infant gaze aversions from the stranger's face (indexing arousal regulation) and pupil dilation (indexing physiological reactivity), longitudinally at 2, 4, 6, and 8 months of age. Multilevel mixed-effects models indicated that more fearful infants took more time to look away from a smiling stranger's face than less fearful infants, suggesting that high-fear infants may have slower arousal regulation. At 2 and 4 months, more fearful infants also exhibited greater and faster pupil dilation before gaze aversions, consistent with greater physiological reactivity. Together, these findings suggest that individual differences in infants' gaze aversions and pupil dilation can index the development of fearful temperament in early infancy, facilitating the identification of, and interventions for, risk factors to social disruptions.

Pupil size and pupillary light reflex in early infancy: heritability and link to genetic liability to schizophrenia

BACKGROUND

Measures based on pupillometry, such as the pupillary light reflex (PLR) and baseline pupil size, reflect physiological responses linked to specific neural circuits that have been implicated as atypical in some psychiatric and neurodevelopmental conditions.

METHODS

We investigated the contribution of genetic and environmental factors to the baseline pupil size and the PLR in 510 infant twins assessed at 5 months of age (281 monozygotic and 229 dizygotic pairs), and its associations with common genetic variants associated with neurodevelopmental (autism spectrum disorder and attention deficit hyperactivity disorder) and mental health (bipolar disorder, major depressive disorder and schizophrenia) conditions using genome-wide polygenic scores (GPSs).

RESULTS

Univariate twin modelling showed high heritability at 5 months for both pupil size (h²  = .64) and constriction in response to light (h²  = .62), and bivariate twin modeling indicated substantial independence between the genetic factors influencing each (r_G  = .38). A statistically significant positive association between infant tonic pupil size and the GPS for schizophrenia was found (β = .15, p = .024), while there was no significant association with the GPS for autism or any other GPSs.

CONCLUSIONS

This study shows that some pupil measures are highly heritable in early infancy, although substantially independent in their genetic etiologies, and associated with common genetic variants linked to schizophrenia. It illustrates how genetically informed studies of infants may help us understand early physiological responses associated with psychiatric disorders which emerge much later in life.