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Changes related to the serotonin system play a key role in the etiology of autism spectrum disorder (ASD). Although we know that platelets are associated with the serotonin system, their relation to ASD has not yet been elucidated. In this study, we aim to investigate platelet parameters in children with ASD. Forty patients with ASD according to Diagnostic and Statistical Manual of Mental Disorders 5 (DSM‐5) and 30 healthy controls were included in the study. A complete blood count was done to measure parameters relating to platelet morphology. Moreover, prothrombin time (PT) and activated partial thromboplastin time (aPTT) were evaluated. Lastly, platelet functions were assessed with a platelet functions analyzer 100 (PFA‐100) device by measuring collagen‐ADP and collagen‐epinephrine (EPI) closure times. There was not a significant difference between the groups in terms of platelet count, mean platelet volume (MPV), platelet distribution width, plateletcrit, PT, or aPTT parameters for ASD patients when compared to the control group (P > 0.05). However, MPV in severe ASD, as quantified by the Childhood Autism Rating Scale, was found to be significantly lower when compared to mild to moderate ASD (P = 0.047). Moreover, in terms of platelet functions, the elongation in collagen‐ADP and collagen‐EPI closure times were significantly higher for the ASD group (P = 0.044). These results may suggest an impairment in platelet functions rather than in platelet morphology for children with ASD. Considering these results, further investigation of thrombocyte functions in the ASD may lead to a better understanding of the pathogenesis of ASD and to the development of our limited knowledge of this disorder. Autism Res 2019, 12: 1069–1076. © 2019 International Society for Autism Research, Wiley Periodicals, Inc. Lay Summary Serotonin is a chemical that is found in brain as wells as in blood cells that function in blood clotting in the human body. There are problems related to serotonin in brains of people who have autism. Thus, blood clotting cells may also be affected in people who have autism. In this study, we compare blood clotting functions of children with autism with that of healthy controls.

The purpose of this study was to investigate the possible relationship between Toxoplasma gondii (Nicolle et Manceaux, 1908) and stuttering. We investigated the seropositivity rate for anti-T. gondii IgG and antibodies by enzyme-linked immunosorbent assay (ELISA) in stuttering children to ascertain a possible relationship between T. gondii infection and stuttering. We selected 65 stuttering children and 65 control children (non-stutterers) to investigate the seropositivity rate of anti-T. gondii antibodies by ELISA. Cranial magnetic resonance imaging (MRI) and scalp electroencephalography (EEG) were also performed in stuttering children. The seropositivity rate of anti-T. gondii IgG antibodies among stuttering children (28%) was significantly higher than in control group (5%; p = 0.001). No abnormality was detected in cranial MRI's of stutttering children and their EEG recordings were also normal. There was no significant difference in seropositivity rate regarding age, genders and residence area. The association between seroprevalence of infection with T. gondii and stuttering may be due to hyperdopaminergic state in brains of patients who are T. gondii-seropositive. Thus, there might be a causal relationship between toxoplasmosis and stuttering.