The three ZNT8 autoantibody variants together improve the diagnostic sensitivity of childhood and adolescent type 1 diabetes

Abstract

Aims: We tested whether autoantibodies to all three ZnT8RWQ variants, GAD65, insulinoma-associated protein 2 (IA-2), insulin and autoantibodies to islet cell cytoplasm (ICA) in combination with human leukocyte antigen (HLA) would improve the diagnostic sensitivity of childhood type 1 diabetes by detecting the children who otherwise would have been autoantibody-negative.

Methods: A total of 686 patients diagnosed in 1996–2005 in Skåne were analyzed for all the seven autoantibodies [arginin 325 zinc transporter 8 autoantibody (ZnT8RA), tryptophan 325 zinc transporter 8 autoantibody (ZnT8WA), glutamine 325 Zinc transporter 8 autoantibody (ZnT8QA), autoantibodies to glutamic acid decarboxylase (GADA), Autoantibodies to islet-antigen-2 (IA-2A), insulin autoantibodies (IAA) and ICA] in addition to HLA-DQ genotypes.

Results: Zinc transporter 8 autoantibody to either one or all three amino acid variants at position 325 (ZnT8RWQA) was found in 65% (449/686) of the patients. The frequency was independent of age at diagnosis. The ZnT8RWQA reduced the frequency of autoantibody-negative patients from 7.5 to 5.4%—a reduction by 28%. Only 2 of 108 (2%) patients who are below 5 years of age had no autoantibody at diagnosis. Diagnosis without any islet autoantibody increased with increasing age at onset. DQA1-B1^*X-0604 was associated with both ZnT8RA (p = 0.002) and ZnT8WA (p = 0.01) but not with ZnT8QA (p = 0.07). Kappa agreement analysis showed moderate (>0.40) to fair (>0.20) agreement between pairs of autoantibodies for all combinations of GADA, IA-2A, ZnT8RWQA and ICA but only slight ( < 0.19) agreement for any combination with IAA.

Conclusions: This study revealed that (1) the ZnT8RWQA was common, independent of age; (2) multiple autoantibodies were common among the young; (3) DQA1-B1^*X-0604 increased the risk for ZnT8RA and ZnT8WA; (4) agreement between autoantibody pairs was common for all combinations except IAA. These results suggest that ZnT8RWQA is a necessary complement to the classification and prediction of childhood type 1 diabetes as well as to randomize the subjects in the prevention and intervention of clinical trials.

Keywords::

• Diabetes mellitus
• GAD65 autoantibodies
• human leukocyte antigen genotype
• IA-2 autoantibodies
• islet cell cytoplasm
• insulin autoantibodies

Acknowledgements

We thank all the participant families and Gabriella Gremsberger, Ida Hansson, Jennifer Hemmendahl, Emma Jacobssen, Mea Pelkonen, Ali Shalouie, Ingrid Wigheden and Annika Winqvist for their excellent technical assistance.

Declaration of interest: Our research is supported, in part, by the Swedish Research Council (Grant 14064), Swedish Child Diabetes Foundation, Swedish Diabetes Association, National Institutes of Health (DK26190), UMAS Fund, the Knut and Alice Wallenberg Foundation and the Skåne County Council for Research and Development, as well as by a grant to Karin Larsson from the Clinical Advisory Board, Kristianstad University. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.