Visual search in neurodevelopmental disorders: evidence towards a continuum of impairment.

Disorders with neurodevelopmental aetiology such as Attention-Deficit/Hyperactivity Disorder (ADHD), Autism Spectrum Disorder (ASD) and Schizophrenia share commonalities at many levels of investigation despite phenotypic differences. Evidence of genetic overlap has led to the concept of a continuum of neurodevelopmental impairment along which these disorders can be positioned in aetiological, pathophysiological and developmental features. This concept requires their simultaneous comparison at different levels, which has not been accomplished so far. Given that cognitive impairments are core to the pathophysiology of these disorders, we provide for the first time differentiated head-to-head comparisons in a complex cognitive function, visual search, decomposing the task with eye movement-based process analyses. N = 103 late-adolescents with schizophrenia, ADHD, ASD and healthy controls took a serial visual search task, while their eye movements were recorded. Patients with schizophrenia presented the greatest level of impairment across different phases of search, followed by patients with ADHD, who shared with patients with schizophrenia elevated intra-subject variability in the pre-search stage. ASD was the least impaired group, but similar to schizophrenia in post-search processes and to schizophrenia and ADHD in pre-search processes and fixation duration while scanning the items. Importantly, the profiles of deviancy from controls were highly correlated between all three clinical groups, in line with the continuum idea. Findings suggest the existence of one common neurodevelopmental continuum of performance for the three disorders, while quantitative differences appear in the level of impairment. Given the relevance of cognitive impairments in these three disorders, we argue in favour of overlapping pathophysiological mechanisms.

Altered peripheral BDNF mRNA expression and BDNF protein concentrations in blood of children and adolescents with autism spectrum disorder.

Findings from molecular genetic studies and analyses of postmortem and peripheral tissue led to the hypothesis that neurotrophins-as crucial moderators of neuroplasticity-impact on the pathophysiology of autism spectrum disorder (ASD). The study projects aimed to complement former results on the role of brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family with fundamental impact on brain development and function. The purpose of this work was to investigate peripheral BDNF mRNA expression and BDNF protein concentrations in ASD as potential surrogates for the effects observed in the central nervous system. In a BDNF protein quantification study, serum concentrations were analyzed using Enzyme-Linked Immunosorbent Assays in 24 male patients with ASD, all with an IQ > 70 (age 13.9 ± 3.0 years) and 20 age- and gender-matched healthy control subjects (age 14.4 ± 2.1 years; p = 0.522). In a further independent project, a BDNF mRNA expression analysis, mRNA levels from total blood were assessed by quantitative real-time polymerase chain reaction in a sample of 16 male ASD patients (age 10.8 ± 2.2), 15 age- and gender-matched healthy controls (age 12.1 ± 2.2) and 15 patients with attention deficit hyperactivity disorder as a clinical control group (age 11.8 ± 2.2; p = 0.207). In the protein quantification project, significantly decreased BDNF serum concentrations were found in ASD cases compared to healthy control children (t = -2.123, df = 42, p < 0.05). Analysis of covariance (ANCOVA) revealed this result in accordance with significant reductions in BDNF mRNA expression in ASD, observed in the mRNA expression study (F = 3.65; df = 2.43; p < 0.05); neither age nor IQ confounded the result, as indicated by ANCOVA (F = 3.961; df = 2.41; p < 0.05, η (2) = 0.162). Our study projects supported the notion that neurotrophins are involved in the pathophysiology of ASD. Further studies may eventually contribute to the identification of distinct peripheral mRNA expression and protein concentration patterns possibly supporting diagnostic and therapeutic processes.

Evidence towards a continuum of impairment across neurodevelopmental disorders from basic ocular-motor tasks.

Findings of genetic overlap between Schizophrenia, Attention-Deficit/Hyperactivity Disorder (ADHD) and Autism Spectrum Disorder (ASD) contributed to a renewed conceptualization of these disorders as laying on a continuum based on aetiological, pathophysiological and neurodevelopmental features. Given that cognitive impairments are core to their pathophysiology, we compared patients with schizophrenia, ADHD, ASD, and controls on ocular-motor and manual-motor tasks, challenging crucial cognitive processes. Group comparisons revealed inhibition deficits common to all disorders, increased intra-subject variability in schizophrenia and, to a lesser extent, ADHD as well as slowed processing in schizophrenia. Patterns of deviancies from controls exhibited strong correlations, along with differences that posited schizophrenia as the most impaired group, followed by ASD and ADHD. While vector correlations point towards a common neurodevelopmental continuum of impairment, vector levels suggest differences in the severity of such impairment. These findings argue towards a dimensional approach to Neurodevelopmental Disorders' pathophysiological mechanisms.