Autoantibodies to ICA12 (SOX-13) are not specific for Type I diabetes

The majority of patients with Type I (insulin-dependent) diabetes mellitus has autoantibodies to insulin, glutamic acid decarboxylase and the tyrosine phosphatase-like protein IA-2. Some patients with Type I diabetes, in particular with adult onset diabetes, have, however, only cytoplasmic islet cell antibodies that could be directed to as yet unknown beta cell autoantigens. Recently, one potential antigen, ICA12, was identified as the high mobility group (HMG) box transcription factor SOX-13. Our aim was to evaluate the diagnostic sensitivity and specificity of autoantibodies to SOX-13 for autoimmune diabetes.

Full-length SOX-13 was cloned from human brain mRNA, expressed by vitro transcription/ translation and used to detect autoantibodies by immunoprecipitation and radioligand assay in patients suffering from autoimmune diabetes or non-organ-specific autoimmune diseases.

We found SOX-13 antibodies to be present in 11 of 125 (8.8%) patients with newly diagnosed Type I diabetes and in 3 of 43 (7.0%) patients with latent autoimmune diabetes in adults. There was no association with age, sex and a particular pattern of diabetes-specific autoantibodies. Similar frequencies of SOX-13 antibodies were found in 84 patients with rheumatic diseases (4.0-11.4%) and 211 healthy control subjects (5.2 %).

Our data indicate that SOX-13 represents a minor target of autoantibodies in patients with autoimmune diabetes. Because SOX-13 antibodies were found not to be disease-specific, we assume they are not helpful in improving the diagnosis and prediction of Type I diabetes.