SCN hyperimmunoglobulinemia is associated with elevated plasma cell counts and APRIL levels. (A) Serum Igs levels were measured by immunoturbidimetry in the patients. (B) Correlation between serum levels of each Ig isotype and BM PC in each patient, using Spearman correlation test. (C) Proportion of plasma cells in the BM, determined by cell morphology assays. Kruskal-Wallis test was applied to evaluate differences among 5 groups. (D) Serum APRIL levels in patients with SCN1 and age-matched healthy control (HC), measured by enzyme-linked immunosorbent assay. The gray area indicates normal reference range for each parameter. The Mann-Whitney test was used for SCN1 and HC comparison; ∗P < .05. Bars represent means ± SD.