Autism: One or many spectrums?

Chloride imbalance in Fragile X syndrome

Developmental changes in ionic balance are associated with crucial hallmarks in neural circuit formation, including changes in excitation and inhibition, neurogenesis, and synaptogenesis. Neuronal excitability is largely mediated by ionic concentrations inside and outside of the cell, and chloride (Cl-) ions are highly influential in early neurodevelopmental events. For example, γ-aminobutyric acid (GABA) is the main inhibitory neurotransmitter of the mature central nervous system (CNS). However, during early development GABA can depolarize target neurons, and GABAergic depolarization is implicated in crucial neurodevelopmental processes. This developmental shift of GABAergic neurotransmission from depolarizing to hyperpolarizing output is induced by changes in Cl- gradients, which are generated by the relative expression of Cl- transporters Nkcc1 and Kcc2. Interestingly, the GABA polarity shift is delayed in Fragile X syndrome (FXS) models; FXS is one of the most common heritable neurodevelopmental disorders. The RNA binding protein FMRP, encoded by the gene Fragile X Messenger Ribonucleoprotein-1 (Fmr1) and absent in FXS, appears to regulate chloride transporter expression. This could dramatically influence FXS phenotypes, as the syndrome is hypothesized to be rooted in defects in neural circuit development and imbalanced excitatory/inhibitory (E/I) neurotransmission. In this perspective, we summarize canonical Cl- transporter expression and investigate altered gene and protein expression of Nkcc1 and Kcc2 in FXS models. We then discuss interactions between Cl- transporters and neurotransmission complexes, and how these links could cause imbalances in inhibitory neurotransmission that may alter mature circuits. Finally, we highlight current therapeutic strategies and promising new directions in targeting Cl- transporter expression in FXS patients.

Autism Spectrum Disorder: Focus on Glutamatergic Neurotransmission

Disturbances in the glutamatergic system have been increasingly documented in several neuropsychiatric disorders, including autism spectrum disorder (ASD). Glutamate-centered theories of ASD are based on evidence from patient samples and postmortem studies, as well as from studies documenting abnormalities in glutamatergic gene expression and metabolic pathways, including changes in the gut microbiota glutamate metabolism in patients with ASD. In addition, preclinical studies on animal models have demonstrated glutamatergic neurotransmission deficits and altered expression of glutamate synaptic proteins. At present, there are no approved glutamatergic drugs for ASD, but several ongoing clinical trials are currently focusing on evaluating in autistic patients glutamatergic pharmaceuticals already approved for other conditions. In this review, we provide an overview of the literature concerning the role of glutamatergic neurotransmission in the pathophysiology of ASD and as a potential target for novel treatments.

Genetics on the neurodiversity spectrum: Genetic, phenotypic and endophenotypic continua in autism and ADHD

How we ought to diagnose, categorise and respond to spectrum disabilities such as autism and Attention Deficit/Hyperactivity Disorder (ADHD) is a topic of lively debate. The heterogeneity associated with ADHD and autism is described as falling on various continua of behavioural, neural, and genetic difference. These continua are varyingly described either as extending into the general population, or as being continua within a given disorder demarcation. Moreover, the interrelationships of these continua are likewise often vague and subject to diverse interpretations. In this paper, I explore geneticists' and self-advocates' perspectives concerning autism and ADHD as continua. These diagnoses are overwhelmingly analysed as falling on a continuum or continua of underlying traits, which supports the notion of "the neurodiversity spectrum", i.e., a broader swath of human neural and behavioural diversity on which some concentrations of different functioning are diagnosed. I offer a taxonomy of conceptions of the genetic, phenotypic, and endophenotypic dimensionality within and beyond these diagnostic categories, and suggest that the spectrum of neurodiversity is characteristically endophenotypic.

The Feedback Session of an Autism Assessment: A Scoping Review of Clinical Practice Guideline Recommendations

This review aimed to assess the quality and content of recommendations for delivering an autism diagnosis, published internationally within clinical practice guidelines. Seventeen relevant guidelines were identified. When methodological information was provided, recommendations for feedback were predominantly formed through consensus. Recommendations consistently included who should attend feedback, the timing and mode of delivery, the clinician's manner, and what should be discussed and/or included in an accompanying report. Specific recommendations were not consistent however, and a number of gaps were identified, such as the inclusion of educators and educational specific recommendations. Although individual variation is necessary for autism diagnosis disclosure, agreement on minimum standards of practice is warranted. Further investigation is required to establish best practice.

Autism and mood disorders

Individuals with autism experience substantially higher rates of mood problems compared to the general population, which contribute to reduced quality of life and increased mortality through suicide. Here, we reviewed evidence for the clinical presentation, aetiology and therapeutic approaches for mood problems in autism. We identified a lack of validated tools for accurately identifying mood problems in individuals with autism, who may present with 'atypical' features (e.g. severe irritability). Risk factors for mood problems in autism appear to be largely overlapping with those identified in the general population, including shared genetic, environmental, cognitive, physiological/neurobiological mechanisms. However, these mechanisms are exacerbated directly/indirectly by lived experiences of autism, including increased vulnerability for chronic stress - often related to social-communication difficulties(/bullying) and sensory sensitivities. Lastly, current therapeutic approaches are based on recommendations for primary mood disorders, with little reference to the neurobiological/cognitive differences associated with autism. Thus, we recommend: 1) the development and validation of (objective) tools to identify mood problems in autism and measure therapeutic efficacy; 2) an interactive approach to investigating aetiologies in large-scale longitudinal studies, integrating different levels of analysis (e.g. cognitive, neurobiological) and lived experience; 3) testing potential treatments through high-quality (e.g. sufficiently powered, blinded) clinical trials, specifically for individuals with autism.

Automated recognition of spontaneous facial expression in individuals with autism spectrum disorder: parsing response variability

BACKGROUND

Reduction or differences in facial expression are a core diagnostic feature of autism spectrum disorder (ASD), yet evidence regarding the extent of this discrepancy is limited and inconsistent. Use of automated facial expression detection technology enables accurate and efficient tracking of facial expressions that has potential to identify individual response differences.

METHODS

Children and adults with ASD (N = 124) and typically developing (TD, N = 41) were shown short clips of "funny videos." Using automated facial analysis software, we investigated differences between ASD and TD groups and within the ASD group in evidence of facial action unit (AU) activation related to the expression of positive facial expression, in particular, a smile.

RESULTS

Individuals with ASD on average showed less evidence of facial AUs (AU12, AU6) relating to positive facial expression, compared to the TD group (p < .05, r = - 0.17). Using Gaussian mixture model for clustering, we identified two distinct distributions within the ASD group, which were then compared to the TD group. One subgroup (n = 35), termed "over-responsive," expressed more intense positive facial expressions in response to the videos than the TD group (p < .001, r = 0.31). The second subgroup (n = 89), ("under-responsive"), displayed fewer, less intense positive facial expressions in response to videos than the TD group (p < .001; r = - 0.36). The over-responsive subgroup differed from the under-responsive subgroup in age and caregiver-reported impulsivity (p < .05, r = 0.21). Reduced expression in the under-responsive, but not the over-responsive group, was related to caregiver-reported social withdrawal (p < .01, r = - 0.3).

LIMITATIONS

This exploratory study does not account for multiple comparisons, and future work will have to ascertain the strength and reproducibility of all results. Reduced displays of positive facial expressions do not mean individuals with ASD do not experience positive emotions.

CONCLUSIONS

Individuals with ASD differed from the TD group in their facial expressions of positive emotion in response to "funny videos." Identification of subgroups based on response may help in parsing heterogeneity in ASD and enable targeting of treatment based on subtypes.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02299700. Registration date: November 24, 2014.

Placental abruption and long-term neurological hospitalisations in the offspring

BACKGROUND

Placental abruption is a major determinant of maternal and perinatal morbidity and mortality, often related to asphyxia and preterm birth. However, the impact of abruption on the long-term morbidity of the offspring is less investigated.

METHODS

We designed a hospital-based cohort study, in which the incidence of long-term neurology-related hospitalisations of offspring to women with and without placental abruption was assessed. All singleton deliveries between 1991 and 2014 were included in the study. Congenital anomalies, perinatal mortality, and multifetal pregnancies were excluded from the analyses. We compared cumulative morbidity incidence using Kaplan-Meier survival curves and estimated the risk for long-term neurological hospitalisations from Cox proportional hazards models after adjustment for putative including maternal age, parity, hypertensive disorders, pre-gestational and gestational diabetes, gender, ethnicity, and year of birth.

RESULTS

Over the 22-year period, 2 202 269 person-years of follow-up, there were 217 910 deliveries of which 0.5% (n = 1003) were complicated with placental abruption. The median (interquartile range) follow-up of children in the abruption and non-abruption groups was 10.3 (4.6, 15.9) and 12.0 (6.3, 16.5) years, respectively. The cumulative incidence of total neurological hospitalisations was comparable between abruption (3.32 per 1000 person-years) and non-abruption (3.16 per 1000 person-years). Abruption was associated with increased rates of cerebral palsy (hazard ratio [HR] 6.71, 95% CI 3.32, 13.58) and developmental disorders (HR 3.36, 95% CI 1.38, 8.13), but not for total neurology-related hospitalisations (HR 1.08, 95% CI 0.78, 1.49).

CONCLUSION

Placental abruption is associated with increased rate of cerebral palsy and developmental disorders in the offspring later in life. This study may define risk factors for childhood neuropsychiatric disorders, enabling early diagnosis and intervention in children with such disorders, and perhaps improving their prognosis.