Development and performance of an enzyme-linked immunosorbent assay for first line screening of glutamic acid decarboxilase (GAD) autoantibodies

POSKUS, EDGARDO; VALDEZ, SILVINA N.; VILLALBA, ANABEL; IACONO, RUBEN F.

Rio de Janeiro, Brasil

Congreso; 13th International Congress of Immunology; 2007

GADA is considered highly predictive marker of type 1 diabetes mellitus and also of the insulin requirement in adult-onset patients presumptively classified as type 2 or with Latent Autoimmune Diabetes in Adults (LADA). The reference radiometric method for GADA (RBA) is expensive, the reagents are unstable and environmentally inappropriate. As GADA assessment is a useful tool for diagnostic support, efforts are being made worldwide to develop more adequate tests for GADA in large populations. We have developed a method for GAD65 expression in E. coli as a thioredoxin fusion protein (TrxGAD65). Then such chimera was used in an ELISA in which GADA form a bridge between the immobilized TrxGAD65 and liquid-phase TrxGAD65-biotin. Sera from 46 RBA/GADA positive type 1 or LADA patients and 40 healthy control subjects were included in a first study. All normal control samples scored negative in both ELISA and RBA. The relative sensitivity of ELISA vs RBA was 76%. In a second study 94 samples from unselected diabetic individuals were screened for GADA using both tests. Thirty seven (39.4%) and 33 (35.1%) serum samples were positive for RBA and ELISA, respectively. From these, 27 were both RBA and ELISA positive whereas 10 sera were only RBA positive and 6 were only ELISA positive. Although RBA exhibited a better sensitivity than ELISA, the latest presenting similar specificity, may be considered a low cost assay useful as a first line screening for GADA.