Antibodies to glutamate receptor subtype 3 (GluR3) are found in some patients suffering from epilepsy as the main disease, but not in patients whose epilepsy accompanies antiphospholipid syndrome or Sneddon's syndrome.

Autoantibodies (Ab's) to the "B" peptide (amino acids 372-395) of glutamate/AMPA receptor subtype 3 (GluR3) are found in serum and cerebrospinal fluid of some patients with different types of epilepsy. Since such anti-GluR3B Ab's can activate and/or kill neurons in vitro and in vivo, they may contribute to epilepsy. To investigate whether anti-GluR3B Ab's may also be relevant to epilepsy when it accompanies some autoimmune-diseases, we tested for these Ab's in patients suffering from epilepsy that accompanies anti-phospholipid syndrome (APS) or Sneddon's syndrome (SNS), both being autoimmune-diseases with frequent neurological complications. We tested 77 pediatric patients whose epilepsy is their main disease; 31 adult patients whose epilepsy accompanies APS (primary or SLE-associated) or SNS; 45 epilepsy-free APS and SNS patients; and 90 healthy controls. Compared to the controls, significantly elevated anti-GluR3B Ab's were found in 22/77 (29%) patients whose epilepsy is their main disease, but in none of the patients whose seizures accompany APS or SNS. Yet, all the APS and SNS patients harbored the characteristic anti-phospholipid Ab's (aPL), directed against cardiolipin and beta2-glycoprotein I, and had lupus anti-coagulant. Thus, anti-GluR3B Ab's are not crossreactive with aPL, and not produced as a non-specific consequence of seizures on the one hand, or autoimmune-diseases on the other. Taken together with new findings accumulated recently in our lab, we suggest that anti-GluR3B Ab's are produced primarily in the periphery due to specific/non-specific "irritation" of the immune system, and that once they reach the brain via a leaky blood-brain barrier they may cause neuronal/glial damage and facilitate the outburst of epilepsy and additional neurological abnormalities. In contrast, the presence of anti-GluR3B Ab's does not seem to increase the probability of developing APS, SNS or the seizures that often accompany these autoimmune-diseases. These findings may have important diagnostic and therapeutic implications.