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There appears to be an association between deficiencies of a number of complement components, particularly of the second component (C2), and rheumatic diseases, especially lupus. The meaning of this association is not clear, but the linkage of deficiency of C2 with HLA, especially HLA-A10, B18, Dw2, as well as with BfS, suggests a possible linkage to immune response genes.
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Peter H. Schur (1978) studied this question.
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