Single-nucleotide genetic variants spanning the <i>MASP1</i> and <i>MASP2</i> genes were analysed for associations with MASP/MAP levels and SLE manifestations.<h4>Results</h4>Patients with MAP-1 serum concentrations in the highest quartile had significantly higher rates of discoid rash (OR 2.8 (95% CI 1.4 to 5.7)), haematological manifestations (OR 2.1 (95% CI 1.1 to 3.7)) and autoantibodies against Sm, RNP, SSA and SSB (ORs 2.4 (95% CI 1.3 to 4.6) to 3.6 (95% CI 1.7 to 7.7)). This evidence concerns the gene MASP1 and systemic lupus erythematosus.