Autoantibodies Against Gad₆₅Rather Than Gad₆₇Precede the Onset of Type 1 Diabetes

Abstract

The enzyme glutamate decarboxylase (GAD) is considered one of the major Beta cell antigens in Type 1 diabetes mellitus. The GAD autoantibody (GAD-AAb) prevalence in newly diagnosed Type 1 diabetic patients has been described up to 80%, depending on the detection method used. The aim of this study was to evaluate a simple, specific, and sensitive radioimmunoassay (RIA) method for detection of AAb against both isoforms of the enzyme, GAD65 and GAD67, in a cross-sectional study using sera from newly diagnosed Type 1 diabetic patients and in a longitudinal study using sera from prediabetic patients and individuals at risk of developing the disease. The 125I-labelled full-length human recombinant proteins of GAD65 and GAD67 expressed in SF9 cells were used as the antigen source. The prevalence of GAD65-AAb in newly diagnosed Type 1 diabetic patients was found to be 73% (112/153), in contrast to 19% (14/72) of GAD67-AAb. Only one patient produced AAb restricted to GAD67. Furthermore, GAD65-AAb could also be detected in 73% (11/15) of prediabetic patients (up to 122 months before clinical manifestation of the disease), whereas only 27% (4/15) of them were positive for GAD67-AAb. In the group at risk of developing Type 1 diabetes, these prevalences were 77% (10/13) and 46% (6/13), respectively. In all GAD67-AAb-positive patients investigated in the longitudinal study, AAb to GAD65 were detectable. In 47% of patients positive for both GAD65-AAb and ICA, the GAD65-AAb appeared by up to 46 months before the occurrence of ICA was detected. The data illustrated that GAD65 is the main immunogenic isoform of the enzyme in the preclinical and clinical stages. The RIA detecting AAb against this isoform may facilitate the screening for individuals at risk of developing the disease.

The cation efflux transporter ZnT8 (Slc30A8) is a major autoantigen in human type 1 diabetes

“…The final list of 68 candidate genes included major known diabetes autoantigens, notably insulin (9), GAD65 (GAD2) (10), IA2 (11), and phogrin (PTPrN2) (16) as well as most of the other putative targets of autoimmunity (heat shock protein 90B (17), carboxypeptidase E (CPE) (18), islet glucose 6 phosphatase-related protein (IGRP) (19), islet amyloid polypeptide (IAPP) (20), pancreatitis-associated protein (humanReg3a/Mouse Reg2) (21), ICA69 (22), imogen 38 (23), peripherin (24), sox13 (25), and GAD67 (GAD1) (26). The appearance of GAD65, CPE, IA2, and phogrin on the list, although gratifying, was surprising, given their known association with neuroendocrine tissues.…”

Diabetes Mellitus-Related Autoantibodies in Childhood Autoimmune Hepatitis

“…Anti-GAD65 antibodies were determined by radioimmunoassay (RSR, UK) 29 . In our control population (5-60 years), the mean ICA value was 0.54 ± 2.27 JDFU (0-10 JDFU).…”

Karlsburg Type I diabetes risk study of a general population: frequencies and interactions of the four major Type I diabetes-associated autoantibodies studied in 9419 schoolchildren

“…For detection of GADA human recombinant GAD65 (Synectics Biotechnology AB, Stockholm, Sweden) was used after iodination as described in detail [14,15]. 20 ml (12 000 cpm) of 125I-GAD65 were incubated with 20 ml serum in duplicates for 18 h at 4°C.…”