Laboratory tests also showed leukopenia (1.71 × 103 cells/μL) with lymphopenia (100 cells/μL), anemia (hemoglobin 9.7 g/dL), thrombocytopenia (115 × 103 cells/μL), elevated serum levels of anti-nuclear antibody (320×, homogeneous and speckled pattern), anti-double stranded DNA (dsDNA) antibody (99.2 IU/mL), and decreased serum level of C3 (31.1 mg/dL). The gene discussed is C3; the disease is Decreased total leukocyte count.