Further, smokers carrying rs4646903 C/C in the CYP1A1 gene that encodes a monooxygenase that generates various reactive oxygen species were also at a significantly increased risk of SLE (OR 9.72, 95% CI 2.73–34.6), as the presence of rs4646903 contributed over 60% excess risk of SLE (145). This evidence concerns the gene CYP1A1 and systemic lupus erythematosus.