This study analyzes the performance of a cell-based anti-GABAAR indirect immunofluorescence assay (IFA; for research use only, EUROIMMUN) using sera from patients with suspected anti-GABAAR encephalitis.

Autoantibodies (AAbs) against Gamma-aminobutyric acid receptors A and B (GABAAR, GABABR) are found in patients with autoimmune anti-GABAR encephalitis. Because of the rareness of anti-GABAAR encephalitis the full spectrum of symptoms is still unknown. Most patients suffer from seizures accompanied by status epilepticus. Treatment of epileptic seizures might be ineffective without simultaneous autoimmune therapy, demonstrating the importance to diagnose this rare form of encephalitis.  

Clinically pre-characterized sera from 30 patients with suspected anti-GABAAR encephalitis were tested for presence of anti-GABAAR and anti-GABABR AAbs with specific cell-based IFAs using GABAAR- or GABABR-transfected cells. Anti-GABAR-positive sera were further investigated with tissue-based IFAs using cryosections of rat hippocampus as well as rat and monkey cerebellum. Serologically pre-characterized samples from 21 patients positive for encephalitis-specific AAbs other than anti-GABAAR served as controls. 

Of the 30 patient sera, one serum was positive for anti-GABAAR and one for anti-GABABR AAbs. AAb positivity was confirmed using tissue-based IFA. All control samples were anti-GABAAR-negative in the cell-based anti-GABAAR IFA, indicating an analytical specificity of 100%.

This cell-based anti-GABAAR IFA shows excellent analytical specificity for the detection of anti-GABAAR AAbs in human serum. Thus, the test provides a diagnostic tool to support recognition of rare anti-GABAAR encephalitis.