AUTOANTIBODIES TO GLUTAMIC-ACID DECARBOXYLASE AND INSULIN IN ISLET-CELL ANTIBODY-POSITIVE PRESYMPTOMATIC TYPE-1 DIABETES-MELLITUS - FREQUENCY AND SEGREGATION BY AGE AND GENDER

The frequency of antibodies to glutamic acid decarboxylase (GAD) and insulin (IAA) in presymptomatic Type 1 diabetes mellitus with a positive test for antibodies to islet cell antigen (ICA) was examined. Thirty-two persons positive for ICA (> 10 JDF units) were tested 2 to 48 months before their ascertained onset of Type 1 diabetes. ICA was quantitated by immunofluorescence as JDF units, anti-GAD by radioimmunoprecipitation and anti-insulin by radioimmunoassay. There was a positive test for anti-GAD in 25 (78 %), and for IAA in 23 (72 %), of the 32 prediabetic ICA-positive subjects. Stratification according to age at the onset of diabetes showed differing frequencies of anti-GAD and IAA in the prediabetic stage. Thus the positivity rate for anti-GAD for 18 subjects older than 10 years at onset of diabetes was 83 %, and for 14 aged 10 or younger at onset was 71 %; conversely, the rate for IAA for 18 subjects older than 10 at onset was 56 % and for 14 aged 10 or less at time of onset was 93 % (p = 0.01). The frequency of anti-GAD was higher in females (88 %) than males (71 %) whereas the frequency of IAA was higher in males (82 %) than in females (60 %). Since autoantibodies to GAD and insulin occur in presymptomatic Type 1 diabetes with differences in frequencies by age and gender, the stimuli to autoimmunity may operate differently at different ages, and may also be gender-related.