High frequency of Smith autoantibodies in Omani patients with systemic lupus erythematosus.

This study was conducted to investigate the frequency and significance of some antinuclear autoantibodies in Omani patients with systemic lupus erythematosus (SLE). Anti-nuclear antibodies (ANA), anti-double stranded-DNA (anti-dsDNA), and anti-Smith (anti-Sm) autoantibodies were investigated in 60 Omani patients clinically diagnosed with SLE according to the American College of Rheumatology Criteria. The SLE group included 57 females and 3 males with an average age of 26 years. In addition, a group of 60 healthy Omanis (26 females and 34 males; average age 25 years) was used as a control. ANA patterns and autoantibody profile were assayed by indirect immunofluorescence assay using Hep-2 cells and liver/kidney/stomach tissue, respectively. Anti-dsDNA were examined by enzyme-linked immunosorbent assays; anti-Sm antibodies were measured by immunoblotting technique. Out of the 60 SLE patients, 59/60 (98.3%) were seropositive for ANA. Anti-dsDNA and anti-Sm each was detected in 50/60 (83.3%) of the Omani patients. The homogenous pattern of ANA was detected in 30/60 (50%) of patients, whereas the frequency of fine-speckled and coarse-speckled was 16/60 (26.7%) and 6/60 (10%), respectively. High titers (≥ 1:320) of ANA was detected in 56/60 (93.3%) of SLE patients. High titers of anti-Sm were detected in 22/60 (33.3%) of patients. High titers (>100 IU/ml) of anti-dsDNA were detected in 40/60 (66.7%) of patients. In the control group, ANA were detected in 8/60 (13.3%) but at low titers, whereas anti-dsDNA and anti-Sm were not detected in the healthy control group. This study shows that anti-Sm is as important as the anti-dsDNA for confirming the diagnosis of SLE and that anti-Sm occurs at a much higher frequency (83.3%) than that reported in other populations indicating the importance of this specific autoantibody for the diagnosis and possibly prognosis of Omani SLE patients.