Autoimmune diseases are characterized by aberrant chronic activation of the immune system which causes tissue inflammation and damage in genetically predisposed individuals . Some studies suggest associations between immune system abnormalities or cytokine aberrations with autism, suggesting that immunological dysregulation is an important comorbidity of autism and may play a role in its pathogenesis, including up regulation of inflammation markers .
Autoantibodies have been detected in patients with behavioral disorders, such as autism . Some studies demonstrated improvement of patients suffering from autism by treatment with intravenous immunoglobulin (IVIG) as shown by a recent pilot study . Autoimmunity to the central nervous system (CNS) may play a pathogenic role in a subgroup of patients with autism. This study aimed to assess plasma anti-ganglioside M1 autoantibodies levels in autistic children and comparing them with normal healthy children.
In our study, the ratio of male to female autistic children who were recruited randomly from the autism clinic in Cairo University Hospitals was about 5 to 1, which is nearly correlated with the study of Ahmedand Abou El-Seoud  who found that the ratio of male to female was ≈ 4 to 1. Also, Wiśniowiecka-Kowalnik and Nowakowska  have mentioned in their study that autism is one of the most prevalent groups of neurodevelopmental disorder that affects around 1–2% of the population with an average male to female ratio of 4–5:1. However, the ratio found in the current study is not representative of the general population due to the small sample size.
In the current study, the mean plasma anti-ganglioside M1 autoantibodies level was significantly higher in 40 autistic patients (3.75 ± 0.62 ng/ml) than in 40 sex- and age-matched control subjects (1.96 ± 0.3 ng/ml) (P value = 0.001). This is in agreement with a study conducted by Yang et al.  who found that autistic children had higher positive levels of anti-ganglioside M1 antibodies (37.8%) than controls (21.67%) (P value = 0.04). Also in line with the results of our study, Mostafa and Al-Ayadhi  observed that autistic children had significantly higher serum levels of anti-ganglioside M1 antibodies than healthy controls (P value < 0.001).
Also, suggesting a possible immunological process in autism, Kern et al.  found that brain autoantibody levels in autistic children were higher than those in the control group. Lekman et. al.  carried out a study on CSF samples obtained from 20 children with autism and 25 controls. He found that anti-ganglioside M1 autoantibodies were significantly increased in patients with autism compared with age-matched controls which is also concordant with the current study.
Careaga et al.  stated that increased anti-phospholipid antibody levels in young children with autism and the association between antibody levels and impaired behaviors in the pediatric population as whole offer potential new targets for understanding the mechanisms involved in the pathogenicity of autism.
Mazur-Kolecka et al.  tested the presence of autoantibodies against human neuronal progenitor cells in sera from children with autism (n = 20) and age-matched controls (n = 18) by immunoblotting and immunocytochemistry. They found that sera from individuals with autism had a higher incidence of autoantibodies than in control sera. Mostafa and Al-Ayadhi also found that autistic children had a significantly higher percentage of serum anti-neuronal antibodies (62.5%) than healthy controls (5%) (P value ≤ 0.001). In addition to the aforementioned studies, a study conducted by Wills et al.  proved that there were autoantibodies against certain neural antigens in autistic patients compared to a normal healthy control group. Also, a study presented by Mostafa and Kitchener  mentioned that children with autism had significantly higher percent seropositivity of anti-nuclear antibodies than healthy children (P value ≤ 0.01).
Moreover, a study conducted by , that included 30 normal and 68 autistic children using immunoblotting assay, found that autistic children but not normal children had antibodies to the caudate nucleus (49% positive sera), cerebral cortex (18% positive sera) and cerebellum (9% positive sera)  analyzed autoantibody repertoires to brain tissue extract in the plasma of 171 autistic children and 54 controls. They showed statistically significant higher levels in children with autism than in the control group. In addition,  found a significant increase in the incidence of (IgG isotype) to neuron-axon filament protein and glial fibrillary acidic protein in autistic subjects. In a cohort study conducted by , it was found that children with autism have a greater frequency of serum antibodies to brain endothelial cells and their nuclei than healthy children. The presence of these antibodies raises the possibility that autoimmunity plays a role in the pathogenesis of language and social developmental abnormalities in a subset of children with these disorders.
On other hand  carried out a study on 42 children (24 males, 18 females) with autism in comparison to 21 (13 males, 8 females) healthy-matched children aged between 2 and 12 years. There was no seropositivity of anti-neuronal antibodies in either of the groups including anti-ganglioside M1 autoantibodies. A possible cause for the discrepancy between the result of this study and our study is that autism is not considered as a typical autoimmune disease, self-reactive antibodies or autoantibodies against a wide variety of targets have been found in a subset of patients with autism. In addition, another study conducted by  suggested that there was no consistent evidence to indicate that the reactivity of plasma from children to neural profiles in the brain is related to an autism diagnosis. Also, in another study by , no difference was found in the rate of occurrence of autoantibodies to cerebellar golgi neurons between children with autism and healthy peers. This finding was not concordant with the current study and the discrepancy may be attributed to the different type of autoantibodies to different target brain tissue measured in both studies and also due to the difference in the technique used, where coronal sections of brain tissue from a rhesus macaque (Macaca mulatta) were used for immunohistochemical analysis in the latter study.
In the present work, children with severe autism had slightly higher levels of anti-ganglioside M1 antibodies (3.77 ± 0.68 ng/ml) than those patients with mild to moderate autism (3.73 ± 0.57 ng/ml), but this difference was statistically insignificant (P value = 0.840). On the other hand,  have found that anti-ganglioside M1 antibodies levels had significant positive correlations with the degree of the severity of autism which may be due to the larger sample size in the latter study. Also,  found that brain autoantibody levels in autistic patients showed significant correlation with autism severity. The children in the latter study were all exposed to mercury that may have elicited the production of autoantibodies, unlike the present study; therefore, this may have led to different results.
Also, in the study conducted by , the frequency of the positivity of serum anti-neuronal antibodies was significantly higher in children with severe autism than children with mild to moderate autism. This finding was not concordant to the results of the present study, probably because the sample size in the latter study was larger (80 patients with autism compared to 80 healthy controls) which may have also contributed to the difference in results.
Further studies with larger sample size as well as multi-center studies are required to delineate the relation between GM1 and disease severity. Also more studies are required to assess and follow-up the effect of different autoimmune therapeutic strategies in treating patients with autism.
Strengths and limitations
The strength in this study is that it evaluates the relation of anti-ganglioside M1 autoantibodies level and the severity of autism in a sample of Egyptian children, not merely its level without relating it to the clinical picture. Among the study limitations is the reduced clinical input which was largely due to global COVID-19 pandemic. In addition, the sample taken was a convenient sample which is another limitation. This study is a cross-sectional study, however a follow up study would more clearly show the relation between the level of anti-ganglioside M1 autoantibodies and autism clinical course over time.