Klinefelter's syndrome (47,XXY) in male systemic lupus erythematosus patients: Support for the notion of a gene‐dose effect from the X chromosome

The frequency of Klinefelter's syndrome (47,XXY), often subclinical, is increased in men with SLE by approximately 14-fold compared with its prevalence in men without SLE. Diagnostic vigilance for 47,XXY in male patients with SLE is warranted. These data are the first to show an association of Klinefelter's syndrome with an autoimmune disease found predominantly in women. The risk of SLE in men with Klinefelter's syndrome is predicted to be similar to the risk in normal women with 46,XX and approximately 14-fold higher than in men with 46,XY, consistent with the notion that SLE susceptibility is partly explained by an X chromosome gene-dose effect.