Familial myasthenia gravis, excluding neonatal myasthenia gravis, occurred in 3.8% of our 702 myasthenic patients and in 3.4% of reported patients, an incidence greater than in the general population (P < 0.001). The disease occurred in siblings (95 patients in 44 families), including six sets of twins, cousins (21 in 9), fathers and children (16 in 6), mothers and children (9 in 4), second cousins (6 in 3), and aunts, uncles, nieces, and nephews (17 in 7). Familial myasthenia gravis resembles the nonfamilial disease in male to female ratio, clinical manifestations, response to anticholinesterase medication, and occasional association with hyperthyroidism or rheumatoid arthritis, but begins at an earlier age, especially in men, tends to have a slow and benign course, and is associated with lower incidence of peripheral muscle involvement, remission, mortality, thymoma, and striation-binding globulin.
Namba T, Brunner NG, Brown SB, Muguruma M, Grob D. Familial Myasthenia Gravis: Report of 27 Patients in 12 Families and Review of 164 Patients in 73 Families. Arch Neurol. 1971;25(1):49–60. doi:10.1001/archneur.1971.00490010059009
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