THE PREVALENCE OF THYROID MICROSOMAL AND THYROGLOBULIN AUTOANTIBODIES IN LIBYAN PATIENTS WITH GRAVES-DISEASE AND IDIOPATHIC MYXEDEMA

The prevalence of thyroid microsomal autoantibodies (TM-ab) and thyroglobulin autoantibodies (TG-ab) was studied in Libyan patients with Graves' disease (GD) and idiopathic myxoedema (MX). There were 98 cases of GD (68 Caucasians + 30 Blacks); 25-40 years of age; 10 males (7 Caucasians + 3 Blacks) and 88 females (61 Caucasians + 27 Blacks) and 100 cases of MX (72 Caucasians + 28 Blacks); 35-55 years of age; 12 males (9 Caucasians + 3 Blacks) and 88 females (63 Caucasians + 25 Blacks). As a control group (CG), 300 healthy Libyans were included in the study (220 Caucasians + 80 Blacks); 20-55 years of age; 40 males (30 Caucasians + 10 Blacks) and 260 females (190 Caucasians + 70 Blacks). The prevalence of the autoantibodies in GD (Caucasians + Blacks) (TM-ab: 68%, TG-ab: 51%) and MX (Caucasians + Blacks) (TM-ab: 75%, TG-ab: 65%) was significantly higher compared with CG (Caucasians + Blacks) (TM-ab: 9.0%, TG-ab: 3.6%) (p < 0.00001). When the subjects were segregated into Caucasians and Blacks, it was observed that the prevalence of both autoantibodies was significantly lower in GD (Blacks) (TM-ab: 47% TG-ab: 26%) and MX (Blacks) (TM-ab: 57%, TG-ab: 50%) compared with GD (Caucasians) (TM-ab: 78%, TG-ab: 62%) (p = 0.002 or 0.001) and MX (Caucasians) (TM-ab: 82%, TG-ab: 71%) (p = 0.05 or = 0.01) respectively. The prevalence of 9.0% and 3.6% for TM-ab and TG-ab respectively in healthy Libyans, CG (Caucasians + Blacks), was comparable with the reports from other parts of the world. However, CG (Blacks) seemed to have lower prevalence for both the autoantibodies compared with CG (Caucasians) (TM-ab: 2.5% vs 11.3%, p = 0.03; TG-ab: 1.2% vs 4.5%, p = 0.32). This finding of dissociation in the prevalence of TM-ab and TG-ab between Blacks and Caucasians was taken as evidence in support of the hypothesis that immunogenetic control of autoimmune thyroid diseases is different in Blacks and Caucasians.