Comment on: Gale EAM (2005) Latent autoimmune diabetes in adults: a guide for the perplexed. Diabetologia 48:2195-2199

Distinct clinical and laboratory characteristics of latent autoimmune diabetes in adults in relation to type 1 and type 2 diabetes mellitus

Ever since its first appearance among the multiple forms of diabetes, latent autoimmune diabetes in adults (LADA), has been the focus of endless discussions concerning mainly its existence as a special type of diabetes. In this mini-review, through browsing important peer-reviewed publications, (original articles and reviews), we will attempt to refresh our knowledge regarding LADA hoping to enhance our understanding of this controversial diabetes entity. A unique combination of immunological, clinical and metabolic characteristics has been identified in this group of patients, namely persistent islet cell antibodies, high frequency of thyroid and gastric autoimmunity, DR3 and DR4 human leukocyte antigen haplotypes, progressive loss of beta cells, adult disease onset, normal weight, defective glycaemic control, and without tendency to ketoacidosis. Although anthropomorphic measurements are useful as a first line screening, the detection of C-peptide levels and the presence of glutamic acid decarboxylase (GAD) autoantibodies is undoubtedly the sine qua non condition for a confirmatory LADA diagnosis. In point of fact, GAD autoantibodies are far from being solely a biomarker and the specific role of these autoantibodies in disease pathogenesis is still to be thoroughly studied. Nevertheless, the lack of diagnostic criteria and guidelines still puzzle the physicians, who struggle between early diagnosis and correct timing for insulin treatment.

GAD autoantibodies and epitope reactivities persist after diagnosis in latent autoimmune diabetes in adults but do not predict disease progression: UKPDS 77

AIMS/HYPOTHESIS

Latent autoimmune diabetes in adults (LADA) is a slowly progressive form of autoimmune diabetes, with autoantibodies to islet proteins developing in older patients who have no immediate requirement for insulin therapy. Markers of its clinical course are uncharacterised. The aim of this study was to determine whether persistence of, or changes in, GAD65 autoantibodies (GADAs) in the LADA patients who participated in the United Kingdom Prospective Diabetes Study (UKPDS) were associated with disease progression or insulin requirement.

METHODS

GADA levels and their relative epitope reactivities to N-terminal, middle and C-terminal regions of human GAD65 were determined in 242 UKPDS patients who were GADA-positive at diagnosis; samples taken after 0.5, 3 and 6 years of follow-up were tested using a radiobinding assay. Comparisons were made of GADA status with clinical details and disease progression assessed by the requirement for intensified glucose-lowering therapy.

RESULTS

GADA levels fluctuated between 0.5 and 6 years but persisted in 225 of 242 patients. No association of GADA levels with disease progression or insulin requirement was observed. Antibody reactivity was directed to C-terminal and middle epitopes of GAD65 in >70% patients, and the N-terminal in <9%. There were no changes in epitope reactivity pattern over the 6 year follow-up period, nor any association between epitope reactivity and insulin requirement.

CONCLUSIONS/INTERPRETATION

GADAs persist for 6 years after diagnosis of LADA, but levels and reactivity to different GAD65 epitopes are not associated with disease progression.