Figure 1.

Heterozygosity of the 28‐bp C2 deletion rs9332736 in systemic lupus erythematosus (SLE) patients and primary Sjögren's syndrome (SS) patients. A, Prevalence of heterozygous carriers of the C2 loss‐of‐function variant rs9332736 in SLE patients (n = 955), primary SS patients (n = 910), and healthy controls (n = 2,262). Individuals homozygous for the rs9332736 variant (2 SLE patients and 1 primary SS patient) were excluded. B, Risk of association with SLE or primary SS according to number of C4A copies in rs9332736, with odds calculated relative to healthy controls. C, Risk of association with SLE or primary SS according to the combined effect of C4A copy number and rs9332736 heterozygosity (ref/del), with odds calculated relative to a C4A copy number of 2 and normal C2 (ref/ref). Due to rs9332736 segregating with C4A, no individuals heterozygous for rs9332736 have 0 C4A copies. Data were analyzed using logistic regression and adjusted for sex (A, B, and C) and C4B copy number (B and C). In B and C, bars show the 95% confidence intervals. D, Linkage disequilibrium (LD; r²) between the 28‐bp C2 deletion rs9332736 and HLA alleles/biallelic single‐nucleotide polymorphisms in the HLA region. LD with HLA alleles for 6 HLA genes are indicated by triangles, including HLA alleles A, C, B, DRB1, DQB1, and DPB1. The vertical gray‐shaded line indicates the genomic position of C2. LD was estimated using SweGen whole‐genome sequencing samples (n = 1,000). Color figure can be viewed in the online issue, which is available at http://onlinelibrary.wiley.com/doi/10.1002/art.42270/abstract.