Clinical and autoimmune features of a patient with autism spectrum disorder seropositive for anti-NMDA-receptor autoantibody

Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by dysfunctions in social interactions resulting from a complex interplay between immunogenetic and environmental risk factors. Autoimmunity has been proposed as a major etiological component of ASD. Whether specific autoantibodies directed against brain targets are involved in ASD remains an open question. Here, we identified within a cohort an ASD patient with multiple circulating autoantibodies, including the well-characterized one against glutamate NMDA receptor (NMDAR-Ab). The patient exhibited alexithymia and previously suffered from two major depressive episodes without psychotic symptoms. Using a single molecule-based imaging approach, we demonstrate that neither NMDAR-Ab type G immunoglobulin purified from the ASD patient serum, nor that from a seropositive healthy subject, disorganize membrane NMDAR complexes at synapses. These findings suggest that the autistic patient NMDAR-Abs do not play a direct role in the etiology of ASD and that other autoantibodies directed against neuronal targets should be investigated.

Trial registration: ClinicalTrials.gov NCT02628808.

Keywords: autism spectrum disorder; autoimmunity; glutamate; infection; single-molecule tracking.

Figures

Figure 1.. NMDAR autoantibodies from the seropositive healthy subject (Healthy+) and the seropositive ASD patient (ASD+) do not differ in their capacity to alter synaptic NMDAR dynamics. (A) Schematic representation of the experimental design. Before tracking GluN2A-NMDAR-QD complexes, hippocampal cultures (13 to 15 days in vitro) were incubated for 30 minutes with different purified type G immunoglobulin (IgG) samples from a seropositive healthy subject from the cohort (Healthy+), a seropositive ASD patient from the cohort (ASD+), or three pooled healthy seronegative subjects (Healthy-). (B) Representative trajectories of GluN2A-NMDAR-QD complexes (500 frames, 50 ms acquisition) at the plasma membrane in the presence of NMDAR-Ab from Healthy+ and ASD+. Synapses (in green) are identified with Mitotracker. Scale bar: 500 nm. (C) Synaptic mean square displacement (MSD) of GluN2A-NMDAR-QD complexes in the absence (Healthy-) or presence (Healthy+, ASD+) of NMDAR-Ab. (D) Cumulative frequency of the synaptic GluN2A-NMDAR-QD complexes diffusion coefficient in the absence (Healthy-) or presence (Healthy+, ASD+) of NMDAR-Ab. (E) Comparison of GluN2A-NMDAR diffusion coefficient in the absence (Healthy-) or presence (Healthy+, ASD+) of NMDAR-Ab at glutamate synapses (median diffusion coefficient ࢱ 25%-75% IQR, Healthy- = 0.107 μm2/s, IQR= 0.034-0.197 μm2/s, n= 492; Healthy+ = 0.089 μm2m/s, interquartile range (IQR) = 0.036-0.185 μm2/s, n= 490; ASD+ = 0.102 μm2/s, IQR= 0.039-0.186 μm2/s, n= 555; P= 0.81 Kruskal-Wallis test). Anti-GluN2A, anti-N-methyl-D-aspartate receptor 2A; ASD, autism spectrum disorder; ASD+, seropositive autism spectrum disorder patient; Cumui. freq., cumulative frequency; Diff. coeff., diffusion coefficient; Healthy+, seropositive healthy subject; Healthy-, seronegative healthy subject; IgG, type G immunoglobulin; QD, quantum dot; MSD, mean square displacement; NMDAR, N-methyl-D-aspartate receptor; NMDAR-Ab, N-methyl-D-aspartate receptor autoantibody.