Genetic factors in myasthenia gravis: a family study.

We studied forty-four patients with myasthenia gravis (MG) and their families. Thirty percent of patients had a confirmed family history of autoimmune disease; in one case this was MG. In all the families with autoimmune disease, the affected relatives were related to the patients through the maternal line. HLA-B8 and DR3 were increased in patients due to the high incidence of these antigens in female, nonthymoma patients with onset before 40 years. HLA-B5 was increased in patients with older onset. The haplotype A1-B8-DR3 was not found to be increased given the presence of B8 or DR3.