Systemic lupus erythematosus (SLE) occurs more frequently among woman than men. We undertook the present study to determine whether the male-female ratio in SLE families is different than expected by chance, and whether excess male fetal loss is found.
All SLE patients met the revised American College of Rheumatology Classification criteria, while SLE-unaffected subjects were shown not to satisfy these same criteria. Putative family relationships were confirmed by genetic testing. Pregnancy history was obtained from all subjects, including unrelated control woman. Adjusted Wald binomial confidence intervals (CI) were calculated for ratio of boys to girls in families and compared to the expected ratio of 1.06
There were 2578 subjects with SLE with 6056 siblings. Considering all subjects, we found 3201 boys and 5434 girls (ratio=0.59, of 95% CI 0.576–0.602). When considering only the SLE-unaffected siblings, there were 2919 boys and 3137 girls (ratio=0.93, 95%CI 0.92–0.94). In both cases, the ratio of males-to-females is statistically different than the known birth rate. Among SLE patients as well as among their sisters and mothers there was an excess of male fetal loss compared to the controls.
Siblings of SLE patients are more likely to be girls than expected. This finding may be in part explained by excess male fetal loss, which is found among SLE patients and their first degree relatives.