Autism Spectrum Disorder in Fragile X Syndrome: Cooccurring Conditions and Current Treatment

Healthy brain function requires a balance between the activity of dopamine receptor 1 (D1) and dopamine receptor 2 (D2). Alterations in this balance increase the risk for numerous developmental brain disorders. Indeed, D1 and D2 expression fluctuates throughout maturation, although there is conflicting evidence regarding the precise changes that occur. Here, we used stereology to investigate the developmental changes in the number of D1‐ or D2‐expressing neurons in the prelimbic cortex, infralimbic cortex (IL), insula cortex, dorsal striatum, and ventral striatum of female and male mice with green fluorescent protein‐tagged D1 or D2. Postnatal day 17, 25, 35, 49, and 70 were examined to cover juvenility to adulthood. In all regions, analysis of D1 density compared to D2 density within each sex seldom detected effects or interactions involving age. However, D1:D2 density ratio changed across age depending on sex. In the IL, D1:D2 density ratio increased in females from adolescence, whereas it was stable in males. In the insula cortex, D1:D2 ratio initially increased in males but decreased in females from juvenility to preadolescence. The ratio then increased in males and females from adolescence to adulthood, with males showing a more dramatic increase. In both the dorsal and ventral striatum, the ratio increased from adolescence. In all regions, females had a higher ratio compared to males throughout maturation except in the insula cortex at P25. These comprehensive observations are novel, and highlight how the maturational changes in the expression of these receptors may contribute to developmental disorders.

Background: Fragile X syndrome (FXS) is the most frequent cause of inherited intellectual disability and the most commonly identified monogenic cause of autism. Recent studies have shown that long-term pathological consequences of FXS are not solely confined to the central nervous system (CNS) but rather extend to other physiological dysfunctions in peripheral organs. To gain insights into possible immune dysfunctions in FXS, we profiled a large panel of immune-related biomarkers in the serum of FXS patients and healthy controls. Methods: We have used a sensitive and robust Electro Chemi Luminescence (ECL)-based immunoassay to measure the levels of 52 cytokines in the serum of n = 25 FXS patients and n = 29 healthy controls. We then used univariate statistics and multivariate analysis, as well as an advanced unsupervised clustering method, to identify combinations of immune-related biomarkers that could discriminate FXS patients from healthy individuals. Results: While the majority of the tested cytokines were present at similar levels in FXS patients and healthy individuals, nine chemokines, CCL2, CCL3, CCL4, CCL11, CCL13, CCL17, CCL22, CCL26 and CXCL10, were present at much lower levels in FXS patients. Using robust regression, we show that six of these biomarkers (CCL2, CCL3, CCL11, CCL22, CCL26 and CXCL10) were negatively associated with FXS diagnosis. Finally, applying the K-sparse unsupervised clustering method to the biomarker dataset allowed for the identification of two subsets of individuals, which essentially matched the FXS and healthy control categories. Conclusions: Our data show that FXS patients exhibit reduced serum levels of several chemokines and may therefore exhibit impaired immune responses. The present study also highlights the power of unsupervised clustering methods to identify combinations of biomarkers for diagnosis and prognosis in medicine.

RNA binding proteins play essential roles during development and aging, and are also involved in disease pathomechanisms. RNA sequencing and omics analyses have provided a window into systems level alterations in neurological disease, and have identified RNA processing defects among notable disease mechanisms. This review focuses on two seemingly distinct neurological disorders, the RNA binding proteins they are linked to, and their newly discovered functional relationship. When deficient, Fragile X Mental Retardation Protein (FMRP) causes developmental deficits and autistic behaviors while TAR-DNA Binding Protein (TDP-43) dysregulation causes age dependent neuronal degeneration. Recent findings that FMRP and TDP-43 associate in ribonuclear protein particles and share mRNA targets in neurons highlight the critical importance of translation regulation in synaptic plasticity and provide new perspectives on neuronal vulnerability during lifespan.