ANTIBODIES TO GAD AND GLYCEMIC CONTROL IN RECENT-ONSET IDDM

OBJECTIVE - To analyze the effect of antibodies to glutamic acid decar boxylase (GAD65Ab) and islet cells (ICA512Ab) on glycemic control earl y in IDDM. RESEARCH DESIGN AND METHODS - GAD65Ab and ICA512Ab were mea sured twice in 35 patients (10 male, 25 female; age 10-40 years) initi ally within 2 years of diagnosis and again 1 year later. The glycosyla ted hemoglobin was measured one to four times each year, and the avera ge glycosylated hemoglobin for the preceding year was calculated each time the antibodies were measured. RESULTS - The mean HbA(1) at the ti me of the initial evaluation was 8.04 +/- 0.30 (reference range 4.7-7. 3% for nondiabetic patients), the average GAD65Ab index was 0.735 +/- 0.306, and the mean ICA512Ab index was 1.94 +/- 0.65. The GAD65Ab inde x correlated with HbA(1) (r = 0.41, P < 0.025). whereas the ICA512Ab i ndex did not (r = 0.13). One year later, the mean GAD65Ab index was 0. 94 +/- 0.34, the mean ICA512Ab index was 1.04 +/- 0.40, and the mean H bA(1) was 9.03 +/- 0.30. The GAD65Ab index correlated with HbA(1) (r = 0.61 P < 0.001), whereas the ICA512Ab index did not ir = -0.06). Stra tification of patients into tertiles according to the average GAD65 in dex revealed, at the follow-up evaluation, that the better glycemic co ntrol in the lowest GAD65Ab tertile was accomplished with significantl y less insulin (0.41 +/- 0.08 U/kg for the lowest tertile vs. 0.71 +/- 0.09 and 0.64 +/- 0.09 for the middle and highest tertiles, respectiv ely; P < 0.05). CONCLUSIONS - In summary, patients with IDDM and low G AD65Ab have better glycemic control even though they require less insu lin. The ICA512Ab index, however, fails to correlate with glycemia.