Monozygotic twins with Klinefelter's syndrome discordant for systemic lupus erythematosus and symptomatic myasthenia gravis.

Monozygotic twins with Klinefelter's syndrome were evaluated for two distinct illnesses. One subject had clinical and serologic evidence of systemic lupus erythematosus and no symptoms of muscle weakness. His identical twin had typical symptoms and laboratory evidence of myasthenia gravis. Antibodies to acetylcholine receptors were present in both subjects. These patients are discussed in relation to genetic, hormonal, and immunologic mechanisms involved in the pathogenesis of these two disorders.