Maternal Thyroid Dysfunction During Pregnancy as an Etiologic Factor in Autism Spectrum Disorder: Challenges and Opportunities for Research

Understanding autism: Causes, diagnosis, and advancing therapies

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition marked by difficulties in social communication, languages, and repetitive behaviors. Its rising prevalence has made it a critical global public health issue. ASD is believed to arise from a combination of genetic and environmental influences. While some gene mutations associated with ASD have been identified, most cases lack clear genetic explanations. Evidence increasingly points to early-life environmental factors as key contributors to ASD, including advanced parental age, maternal diabetes during pregnancy, infections, hormonal imbalances, certain medications, and exposure to air pollution. Currently, ASD diagnosis relies on behavioral assessments, but the absence of specific molecular biomarkers poses significant obstacles to early detection and targeted therapies. Encouragingly, research has identified potential biomarkers, such as neuroimaging classifiers, electroencephalography patterns, eye-tracking data, digital analytics, gene expression profiles, inflammatory and chemokine markers, proteomic and metabolomic profiles, and gut microbiota characteristics. Potential therapeutical strategies under investigation include digital therapies, non-invasive brain stimulation, antioxidants, oxytocin, AVPR1a antagonists, PPAR agonists, and mTOR inhibitors. This review explores ASD across five areas: epidemiological trends, genetic mechanisms, early-life environmental factors and their potential roles, diagnostic biomarkers, and therapeutic approaches.

Association of Thyroid Hormone and Insulin-Like Growth Factor-1 Levels With Autism Spectrum Disorders: A Systematic Review and Meta-Analysis

The action of the thyroid hormones and insulin-like growth factor 1 (IGF-1) is interdependent. The levels of thyroid hormone and IGF-1 were reported to be altered in individuals with autism spectrum disorder (ASD), but the results were controversial. This study aims to compare levels of thyroxine, triiodothyronine, thyroid stimulating hormone, and IGF-1 between the ASD group and neurotypical controls. PubMed, Web of Science, Cochrane, and Embase databases were searched for eligible observational studies. We calculated pooled standardized mean difference (SMD) with 95% confidence intervals (CIs) of our data using a random or fixed effect model. The search strategy provided a total of 1710 articles, of which 16 articles were quantitatively analyzed. The total number of included participants was 2399 (1285 cases and 1114 controls). The meta-analysis revealed no significantly changed blood levels of thyroxine, free triiodothyronine, free thyroxine, and IGF-1 of subjects with ASD compared to non-autistic controls. The blood TSH levels were significantly lower in ASD subjects than in controls (n = 859, Hedges' g = -1.18, 95% CI: -2.17 to -0.20, p = 0.02). Subgroup-analysis results showed that blood free triiodothyronine (n = 153, Hedges' g = -0.74, 95% CI: -1.08 to -0.40, p < 0.0001, I2 = 2%), free thyroxine (n = 153, Hedges' g = -0.72, 95% CI: -1.31 to -0.14, p = 0.02, I2 = 66%), and IGF-1 (n = 397; Hedges' g = -0.92; 95% CI: -1.30 to -0.55, p < 0.00001, I2 = 63%) levels were significantly reduced in subjects with severe ASD symptoms. Individuals with severe ASD may experience a dysfunction of the hypothalamic-pituitary-thyroid axis, and further studies are warranted to determine the correlation between thyroid hormone and IGF-1 levels and disease severity. Trial Registration: ClinicalTrials.gov identifiers: NCT01970345.

Convergence on CaMK4: A Key Modulator of Autism-Associated Signaling Pathways in Neurons

Although the precise underlying cause(s) of autism spectrum disorder remain unclear, more than 1000 rare genetic variations are associated with the condition. For many people living with profound autism, this genetic heterogeneity has impeded the identification of common biological targets for therapy development for core and comorbid traits that include significant impairments in social communication and repetitive and restricted behaviors. A substantial number of genes associated with autism encode proteins involved in signal transduction and synaptic transmission that are critical for brain development and function. CAMK4 is an emerging risk gene for autism spectrum disorder that encodes the CaMK4 (calcium/calmodulin-dependent protein kinase 4) enzyme. CaMK4 is a key component of a Ca2+-activated signaling pathway that regulates neurodevelopment and synaptic plasticity. In this review, we discuss 3 genetic variants of CAMK4 found in individuals with hyperkinetic movement disorder and comorbid neurological symptoms including autism spectrum disorder that are likely pathogenic with monogenic effect. We also comment on 4 other genetic variations in CAMK4 that show associations with autism spectrum disorder, as well as 12 examples of autism-associated variations in other genes that impact CaMK4 signaling pathways. Finally, we highlight 3 environmental risk factors that impact CaMK4 signaling based on studies of preclinical models of autism and/or clinical cohorts. Overall, we review molecular, genetic, physiological, and environmental evidence that suggest that defects in the CaMK4 signaling pathway may play an important role in a common autism pathogenesis network across numerous patient groups, and we propose CaMK4 as a potential therapeutic target.

Impact of Autism on the Relation Between Sleep and Life Satisfaction in Japanese Adults

BACKGROUND/OBJECTIVES

Sleep disorders, such as short sleep, are common comorbidities in individuals with autism spectrum disorder (ASD). Sleep quality and duration are directly associated with quality of life (QOL). Clarifying the influence of ASD on the association between short sleep duration and life satisfaction is an efficient way to improve the QOL of patients with ASD.

METHODS

To clarify the influence of ASD on the association between short sleep duration and life satisfaction scale scores, we conducted a web-based cross-sectional study involving 3823 Japanese adults aged 20-64 years.

RESULTS

In all the participants, a significant inverse association was observed between short sleep duration and life satisfaction. The adjusted odds ratio (OR) and 95% confidence interval (CI) of short sleep for one standard deviation (SD), the increment of life satisfaction scale (2.5 for men and 2.4 for women), was 0.76 (0.70, 0.82). When the analyses were stratified by ASD status, a significant inverse association was observed only among participants without ASD. The corresponding ORs (95% CIs) were 0.73 (0.67, 0.80) and 1.08 (0.85, 1.39) for those with and without ASD. Patients with ASD also showed a significant interaction effect on the association between short sleep duration and life satisfaction.

CONCLUSIONS

Only participants without ASD showed a significant inverse association between short sleep duration and life satisfaction. Although further investigations are necessary, these results can help clarify the mechanism underlying the association between QOL, short sleep duration, and ASD.

Gestational hypothyroxinemia induces ASD-like phenotypes in behavior, proinflammatory markers, and glutamatergic protein expression in mouse offspring of both sexes

Background

The prevalence of autism spectrum disorder (ASD) has significantly risen in the past three decades, prompting researchers to explore the potential contributions of environmental factors during pregnancy to ASD development. One such factor of interest is gestational hypothyroxinemia (HTX), a frequent condition in pregnancy associated with cognitive impairments in the offspring. While retrospective human studies have linked gestational HTX to autistic traits, the cellular and molecular mechanisms underlying the development of ASD-like phenotypes remain poorly understood. This study used a mouse model of gestational HTX to evaluate ASD-like phenotypes in the offspring.

Methods

To induce gestational HTX, pregnant mice were treated with 2-mercapto-1-methylimidazole (MMI), a thyroid hormones synthesis inhibitor, in the tap-drinking water from embryonic days (E) 10 to E14. A separate group received MMI along with a daily subcutaneous injection of T4, while the control group received regular tap water during the entire pregnancy. Female and male offspring underwent assessments for repetitive, anxious, and social behaviors from postnatal day (P) 55 to P64. On P65, mice were euthanized for the evaluation of ASD-related inflammatory markers in blood, spleen, and specific brain regions. Additionally, the expression of glutamatergic proteins (NLGN3 and HOMER1) was analyzed in the prefrontal cortex and hippocampus.

Results

The HTX-offspring exhibited anxious-like behavior, a subordinate state, and impaired social interactions. Subsequently, both female and male HTX-offspring displayed elevated proinflammatory cytokines in blood, including IL-1β, IL-6, IL-17A, and TNF-α, while only males showed reduced levels of IL-10. The spleen of HTX-offspring of both sexes showed increased Th17/Treg ratio and M1-like macrophages. In the prefrontal cortex and hippocampus of male HTX-offspring, elevated levels of IL-17A and reduced IL-10 were observed, accompanied by increased expression of hippocampal NLGN3 and HOMER1. All these observations were compared to those observed in the Control-offspring. Notably, the supplementation with T4 during the MMI treatment prevents the development of the observed phenotypes. Correlation analysis revealed an association between maternal T4 levels and specific ASD-like outcomes.

Discussion

This study validates human observations, demonstrating for the first time that gestational HTX induces ASD-like phenotypes in the offspring, highlighting the need of monitoring thyroid function during pregnancy.