Combined analysis of long-term anti-beta-cell humoral reactivity in type 1diabetes with and without thyroid disease

The prevalence and levels of islet-cel[ antibodies (ICA) decrease in the ye ars following diabetes onset but may persist, particularly in patients with concomitant autoimmune disease. The aim of this cross-sectional study was to investigate the frequencies, associations and levels of the major anti-b eta-cell antibodies in long-standing diabetic patients (median duration : 1 4 years; range 5-47 years) with and without autoimmune thyroid disease (ATD ) in order to consider the specific anti-pancreatic immunologic features as sociated with endocrine autoimmunity. Both ICA and glutamic acid decarboxyl ase (GAD) antibody (GAD-A) frequencies were increased in diabetic patients with ATD (38 vs 23 %, p = 0.03 and 70 vs 21 %, p < 10(-4) respectively). Al though IA2-A frequency tended to be higher in diabetic patients with ATD, n o significant difference was seen (37 vs 26 %, p = 0.14). GAO median level was significantly higher in the diabetic group with ATD (15 vs 5 units, p < 10(-4)). [AZ-A and ICA median levels were similar in both groups. Regardle ss of the combined analysis performed (ICA/GAD-A, ICA/IA2-A or GAD-A/IA2-A) , the prevalence of combined antibody positivity was higher in diabetic pat ients with than without ATD. In bath diabetic populations, ICA and GA-DA we re significantly associated (p < 10-4), and their levels were correlated (r = 0.42, p < 10(-4) and r = 0.584, p < 10(-4) respectively). No significant correlation was seen between IA2-A levels and either ICA or GAD-A titres. It is concluded that Type 1 diabetes mellitus with ATD is characterised by increased persistent humoral islet-related reactivity, particularly directe d towards GAD.