Objective: We aimed to clarify biomarkers and pathogenic autoantibodies in cerebellar ataxia, especially multiple system atrophy (MSA) and immune-mediated cerebellar ataxias (IMCAs), by detection of antigens in serum.

Background: Cerebellar ataxia can be categorized by its mechanisms into hereditary, infectious, drug-induced, neurodegenerative and immune-mediated. It is often difficult but is very important to distinguish these mechanisms in cerebellar ataxia patients. Early MSA-C patients often present with only cerebellar ataxia and there are no serum biomarkers. Therefore, early diagnosis of MSA-C is difficult. IMCAs are attributed to various neuronal antibodies against cell surface or intracellular antigens and they are often associated with paraneoplastic neurological syndromes. It is important to measure these antibodies in patients with IMCAs. However, IMCAs may be diagnosed because of a good immunotherapy response despite neuronal antibodies being of negative in a clinical examination. There are two main reasons: the number of reported neuronal antibodies is too large to examine all of them and unknown neuronal antibodies associated with cerebellar ataxia may be remaining. In this study, we tried to identify specific antigens in serum of patients with MSA and IMCAs.

Method: We selected seven patients with cerebellar ataxia and one normal control. Three cases were probable MSA-C, one case was definite MSA-P, and the other cases were suspected IMCAs. We performed immunoprecipitation of serum and mass spectrometry to detect specific antigens in MSA and IMCAs.

Results: Five patients including two patients with probable MSA-C and three patients with suspected IMCAs were treated with immunotherapy. Two patients with IMCAs showed a good response to immunotherapy, but the other patients showed no response. We detected some antigens including ion channels and transporters on cell membranes in the patients with IMCAs. However, we could not detect specific and common antigens in the MSA patients. In the future, we will examine antibodies to these antigens in the serum of patients by a cell-based assay and Western blotting to identify specific antibodies in  patients with IMCAs.

Conclusion: We detected some antigens including ion channels and transporters on cell membranes in patients with IMCAs by immunoprecipitation of serum and mass spectrometry.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/detection-of-specific-antigens-in-immune-mediated-cerebellar-ataxias/