The familial occurrence of myasthenia gravis 1-3 and of rheumatoid arthritis 4,5 and the concurrence of the two diseases in the same patient 1,6,7 have been reported to be more frequent than can be explained by chance. This communication describes the first report of the simultaneous familial occurrence of myasthenia gravis and rheumatoid arthritis in a brother and sister, and reviews the familial occurrence of these diseases.
The patients were a brother and sister who had rheumatoid arthritis and died of myasthenia gravis. They had two additional brothers and two sisters. One brother had ptosis and diplopia attributed to "nerve paralysis" at the age of 40 years. At the age of 59 years, he still had limitation of lateral movement of the right eye by 10 degrees, and of the left eye by 5 degrees. Another brother, aged 63 years, had rheumatoid arthritis with swelling of the proximal