CD40LG and systemic lupus erythematosus: The depressed IgM levels seen in female relatives are of interest in relation to the low levels that were seen in some 17% of SLE patients.4 It has been reported that patient levels of IgM decline with increasing duration of disease.6,7 However, as many as 6% of first-degree relatives of SLE patients may develop the disease,8 so that the finding of low blood IgM levels in female relatives suggests that the low level seen in patients is at least in part a primary genetic or environmental manifestation of their disease.