Identification of Maternal Antibody Targets in Autism

Background: Previous observations of fetal-brain reactive maternal IgG antibodies in a subset of mothers of children with autism spectrum disorder (ASD), and an association between presence of these antibodies and severe behavioral manifestations led us to undertake identification of the protein targets of these antibodies. Fetal exposure during gestation to brain-reactive maternal IgG may be the underlying cause of the behavioral symptoms noted in some ASD cases and unraveling the molecular interactions between these antibodies and their targets may open new avenues for treatment and prevention.

Objectives: The focus of this project was to identify the molecular targets of ASD associated, fetal-brain reactive maternal IgG antibodies. 

Methods: A protein extract derived from fetal Rhesus macaque brain (152 day gestation) was fractionated by molecular weight and individual fractions were probed with diluted plasma from mothers of children with ASD. Fractions containing antigenic proteins were subjected to duplicate 2-dimensional gel electrophoresis, with one gel being transferred to nitrocellulose and probed with diluted maternal plasma to pinpoint the antigen location, and the other used for spot picking and tandem MS/MS analysis. Verification of mass spectrometric results was carried out using commercially available purified or recombinant proteins, and further confirmed using blocking studies. Reactivity to the identified protein antigens was determined in a sample of 169 mothers of children with ASD and 149 mothers of typically developing children.

Results: Four proteins were identified and confirmed to be the primary antigenic targets of ASD-associated maternal IgG. The 37kDa antigen is an essential metabolic enzyme with well characterized functions in neurogenesis. The 39kDa antigen is an enzyme known to regulate post-synaptic targeting. Two proteins were identified as 73kDa antigens – one that is critical for neuronal growth cone collapse and another that functions as a chaperone for several heat-shock proteins. Confirmed reactivity to the 37kDa and both of the 73kDa proteins is observed exclusively among mothers of children with ASD with a prevalence of approximately 8%, yielding an odds ratio of 26 (95% CI: 1.5-438) 

Conclusions: Maternal IgG reactivity to the protein antigens identified in this study constitutes the most significant biomarker of ASD risk identified to date. In our study sample, reactivity to the 37kDa and 73kDa proteins was observed in approximately 8% of mothers of children with ASD and absent in mothers of typically developing children yielding a highly significant association with ASD (p=0.0003). Furthermore, previous findings from our group and others indicate that such maternal antibodies are often present during pregnancy, supporting the hypothesis that they could play a causal role in precipitating the behavioral outcomes noted in some cases of ASD.