Antibodies to GAD in Diabetic Patients with Chronic Hepatitis C
There is a documented relationship between hepatitis C virus (HCV) infection and evidence of autoimmune thyroid disease. (AITD). 1 Furthermore titres of glutamic acid decarboxylase (GAD) antibodies, one of the markers for autoimmune insulitis, are higher in patients with AITD than in controls. We have therefore examined the status of antithyroid and GAD antibodies in diabetic patients with chronic hepatitis C.
Sera from 63 diabetic patients (46 men and 17 women; mean age, 62.2 Β± 8.9 years), all with chronic hepatitis C diagnosed serologically and histologically were tested for anti-GAD and anti-thyroid (anti-thyroglobulin and anti-microsomal) autoantibodies. The diagnosis of diabetes was established, following a 75g oral glucose tolerance test, based on the guidelines of the World Health Organization, and Type 1 diabetic patients were not included. No patient had received interferon. GAD antibodies were measured by a radioimmunoassay (RIA) kit using human recombinant GAD 65 as an antigen (RSR Limited, Cardiff, UK) (antithyroglobulin antibodies by a particle agglutination test (PA) or a RIA and antimicrosomal antibodies detected by a PA.
Eight of 46 (17.4 %) men and 4 of 17 (23.5 %) women had anti-thyroid autoantibodies. One of the men and 2 of the women had subclinical hypothyroidism, and 1 woman had hyperthyroidism. Anti-GAD antibodies were however under measurable range (i.e. 1.3 U ml -1 ) in all patients.
Hieronimus et al. 3 have recently reported that only 1 of 47 chronic hepatitis C patients, a known case of Type 1 DM, had anti-GAD antibodies. In this study, we have found no anti-GAD antibodies in diabetic patients with hepatitis C, even in patients with AITD. Although the number of subjects was small, these results suggest that HCV rarely contributes to the occurrence of GAD antibodies. However, it is now well recognized that interferon therapy for chronic viral hepatitis can precipitate IDDM. 4 Further study is needed to clarify whether interferon may induce the occurrence of GAD antibodies preferentially in chronic HCV-infected patients.