GABAB receptor autoantibody frequency in service serologic evaluation.
OBJECTIVE
Small-cell lung carcinoma (SCLC) and limbic encephalitis are recognized γ-aminobutyric acid-B receptor (GABABR) autoantibody accompaniments. We sought to determine in a diagnostic serology laboratory the frequency and accompaniments (neurologic, oncologic, and serologic) of GABABR-immunoglobulin G (IgG).


METHODS
We tested stored serum and CSF specimens from 3 patient groups for GABABR-IgG by indirect immunofluorescence on mouse brain tissue and transfected HEK293 cells. Group 1 included 3,989 patients tested for GABABR-IgG in service evaluation for suspected autoimmune encephalopathy. Group 2 included 49 patients with an unclassified CNS synaptic IgG detected (antedating descriptions of GABABR autoantibody). Group 3 included 384 patients in whom ≥1 SCLC-predictive autoantibodies had been detected.


RESULTS
GABABR-specific IgG was detected in 17 patients (serum, 14; CSF, 11). N-type calcium channel antibody coexisted with GABABR-IgG in all seropositive patients of groups 1 and 2. In group 1, 7 of 3,989 patients were positive (0.2%). All had limbic encephalitis; 5 had SCLC. Four patients received immunotherapy and improved neurologically. In group 2, 5 of 49 patients were positive (10%). Three had limbic encephalitis, 1 had rapidly progressive encephalomyelopathy, and 1 had cerebellar ataxia. Two patients had SCLC and 1 had multiple myeloma. In group 3, 5 of 384 patients were positive (1.3%); titers were low (detected only by transfected cell assay). The neurologic presentations were diverse and attributable to coexisting T-cell-mediated autoimmunity (indicated by CRMP-5 IgG [2], ANNA-1 [2], and ANNA-3 [2]), rather than to GABABR-IgG.


CONCLUSIONS
GABABR autoantibody is a marker of an uncommon but treatable paraneoplastic neurologic disorder, usually occurring in the setting of limbic encephalitis and SCLC.
Department of Neurology, Mayo Clinic College of Medicine, Rochester, MN, USA.
Oliver J
OJ
Jeffery
Vanda A
VA
Lennon
Sean J
SJ
Pittock
Jeremy K
JK
Gregory
Jeffrey W
JW
Britton
Andrew
A
McKeon
D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000096:biosynthesis* / Q000097:blood; D001927:Brain Diseases / Q000097:blood / Q000175:diagnosis; D004660:Encephalitis; D005260:Female; D057809:HEK293 Cells; D050031:Hashimoto Disease / Q000097:blood / Q000175:diagnosis; D006801:Humans; D007074:Immunoglobulin G / Q000096:biosynthesis* / Q000097:blood; D008297:Male; D008875:Middle Aged; D018080:Receptors, GABA-B / Q000276:immunology*; D012698:Serologic Tests / Q000592:standards; D055815:Young Adult
D001323:Autoantibodies; D007074:Immunoglobulin G; D018080:Receptors, GABA-B