Two of the five participants with absolute insulin deficiency in our study fit these criteria, having high GAD titres (>2000 units/ml, reference value >64 units/ml); however, with three participants with a confirmed absolute insulin deficiency not exhibiting GAD antibodies, it suggests that the presence of these antibodies is not a sensitive test for detecting the development of absolute insulin deficiency in those with long‐standing diabetes. This evidence concerns the gene GAD1 and diabetes mellitus.