Epidemiology
The rate of SLE varies considerably between countries, ethnicity, gender, and changes over time. In the United States, one estimate of the prevalence of SLE is 53 per 100,000.; other estimates range from 322,000 to over 1 million. In Northern Europe the rate is about 40 per 100,000 people. SLE occurs more frequently and with greater severity among those of non-European descent. That rate has been found to be as high as 159 per 100,000 among those of Afro-Caribbean descent.
SLE, like many autoimmune diseases, affects females more frequently than males, at a rate of almost 9 to 1. This is due to the presence of two X chromosomes in the female as opposed to the one X chromosome present in males. The X chromosome carries immunological related genes, which can mutate and contribute to the onset of SLE. The Y chromosome has no identified mutations associated with autoimmune disease.
The incidence of SLE in the United States increased from 1.0 in 1955 to 7.6 in 1974. Whether the increase is due to better diagnosis or to increasing frequency of the disease is unknown.
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