Acetylcholine receptor antibody characteristics in myasthenia gravis. III. Patients with low anti-AChR antibody levels.

Twenty-five myasthenia gravis (MG) patients whose anti-acetylcholine receptor (anti-AChR) titres against denervated human leg AChR fell in the range of less than 0.1-2.0 nM were tested against AChR preparations from normal human leg muscle, and from human extra-ocular muscle, and the results compared with those of sera with titres greater than 2.0 nM. Seven sera failed to react appreciably with any of the AChR. Many of the remaining 18 low titre sera reacted better with normal leg and ocular AChR than with denervated AChR. In contrast, sera from patients with high anti-AChR titres generally reacted better with denervated, AChR, and as a group this was significantly different from the low titre patients. Sera reacting better with ocular AChR are not restricted to patients with purely ocular symptoms. The results indicate a subgroup of myasthenia gravis patients who have low titres, tend to be male and have relatively mild disease. The aetiology of the autoimmune disorder in this subgroup may differ from that in other MG patients.