SummaryThe serum of 100 patients with myasthenia gravis and 441 of their first-degree relatives was studied for the presence of autoantibodies against several antigens. Antibodies to skeletal muscle were present in 22% of the patients and in 2% of the relatives. Both these frequencies were significantly higher than those in matched control subjects. Also, antinuclear antibodies were present more often both in the patients and in the relatives. Typing for HL-A antigens had shown a positive correlation between HL-A 8 and myasthenia gravis which was significantly higher in women than in men. Antibodies to skeletal muscle and thymomas were found to be much rarer in HL-A 8-positive patients than in HL-A 8-negative patients; HL-A 8-positive patients acquired the disease at an earlier age.HL-A 2-positive patients more often had thymomas and antibodies to skeletal muscle than HL-A 2-negative patients; HL-A 2-positive patients acquired myasthenia gravis at a later age.The fact that the clinical aspects of the HL-A 8-negative and HL-A 2-positive patients were different from those of the HL-A 8-positive and HL-A 2-negative patients justifies the hypothesis that there are two forms of myasthenia gravis.

The sera of 67 patients with thymomas-43 with myasthenia gravis (thymoma(+) MG(+)) and 24 without myasthenia gravis (thymoma (+) MG (-)) from 5 Dutch centers were examined with the indirect immunofluorescence test for the presence of antibodies reacting with skeletal muscle (AMA), thyroid tissue, gastric parietal cells, adrenocortex and antinuclear antibodies (ANA). The data were compared with those obtained in a group 83 MG patients in whom a thymoma was excluded by histological verification (thymoma (-) MG (+)) and with 1106 controls from the normal population. Histocompatibility (HL-A) antigens were tested in 24 thymoma (+) MG (+), 23 thymoma (+) MG (-), and 43 thymoma (-) MG (+) patients and 533 controls from the Dutch population. AMA was found in all thymoma (+) MG (+) cases, in 42% of thymoma (+) MG (-), in 11% of thymoma (-) MG (+), and in less than 1% of the controls. The differences between each of these groups are significant (p less than 0.01, Table 3.) ANA was found in 54%, 50%, 18%, and 4%, respectively, of the above mentioned groups. The differences between the thymoma (+) and the thymoma (-) groups are significant (p less than 0.001. Table 4). The frequencies of antibodies reacting with thyroid tissue, gastric parietal cells and adrenocortex were low and showed no differences between the groups. The frequencies of HL-A8 were significantly decreased in both thymoma groups that had a relatively high incidence of associated immunological disorders (Table 5). Patients with MG and without antimuscle antibodies have no thymomas: This rule is of practical value in the management of the MG patient.

Actin has been purified from varius non-muscle cells and characterized by its molecular weight and ability to polymerize into filaments. Although the occurrence of this protein has been postulated in the mammalian eye lens after observation of actin-like filaments in the electron microscope, definite (bio)chemical proof has been provided only recently. Amino acid analysis, peptide mapping and affinity chromatography revealed the identity of lens actin with the corresponding protein in other tissues. As the filaments could be obtained by co-isolation with highly purified lens plasma membranes, we were interested to know how the actin-containing structures wre located in situ. In the experimental approach reported here, the indirect immunofluorescence technique (IFT) was applied to unfixed cryostat sections of lens tissue. The distribution of actin in calf, rat and pigeon lens is described, and evidence from this for the role of actin in visual accommodation discussed.

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