Gene copy-number variation and associated polymorphisms of complement component C4 in human systemic lupus erythematosus (SLE): Low copy number is a risk factor for and high copy number is a protective factor against SLE susceptibility in European Americans

The C4 gene copy-number variation (CNV) was investigated in 1241 European Americans, including patients with systemic lupus erythematosus (SLE), their first degree relatives by defining genotyping and phenotyping techniques. The results show that gene copy number of gene CNV provides data for an important immune defense protein in health and disease suggesting that low copy number is a risk factor for and high copy number is a protective factor against susceptibility to human SLE.