The predictive value of diabetes-related antibodies in children with type 1 diabetes mellitus and their siblings

The purpose of this study is to screen for diabetes-related antibodies in newly diagnosed type I diabetes Saudi children, and their non-diabetic siblings. We studied 69 newly diagnosed type 1 diabetic Saudis (35 girls, 34 boys), 60 non-diabetic siblings (1 to 17 years), and 42 age- and sex-matched controls not having type 1 diabetes. Their sera were tested for insulin autoantibodies (IAA), antibodies to glutamic acid decarboxylase (GAD65A) and protein tyrosine phosphatase-2 antibodies (IA-2) using ¹²⁵I radioimmunoassays. Fifty-two percent of patients were significantly positive for IAA compared to controls (4.9 %). A total of 50.7 % of patients were also significantly positive for IA-2 compared to controls (4.8 %) (p < 0.0001). GAD65 antibody was detected in 81.2 % of the patients and in none of the controls (p < 0.0001). Both IAA and IA-2 are significantly higher among younger age group, unlike GAD65A, which is significantly higher among older age groups. In non-diabetic siblings, the frequencies of IAA, IA-2, and GAD65A were 6.8, 5.2, and 10.2 % (0.039), respectively, which were higher than in controls. IAA and IA-2 titers were significantly high among younger age group (<0.027), and GAD65A is significantly higher among older age group. A total of 21.6 % of diabetics were positive for all the three antibodies and 3.4 % in siblings. A total of 35.3 % were positive for two antibodies and none in siblings, while 39.2 % were positive for one antibody and 11.9 % in siblings. The combined GAD65 and IA-2 was positive in 81.3 % of young age, 80 % of middle, and in 100 % of the old age group. The screening of type 1 diabetes among Saudis showed the presence of diabetes-related antibodies in 96.1 % of all newly diagnosed patients, compared to 11.9 % of controls (non-diabetic siblings). IAA and IA-2 were significantly higher among younger age groups; GAD65A was significantly higher among older age. The combined GAD65 and IA-2 tests can be considered as a sensitive marker for predicting the occurrence of the disease in individuals at risk of type 1 diabetes in Saudis.