ZnT8 autoantibody titers in type 1 diabetes patients decline rapidly after clinical onset

Abstract

Autoantibodies to the islet-specific zinc transporter isoform 8 (ZnT8) are detected in the majority of type 1 diabetes patients prior to and at clinical diagnosis. The presence of ZnT8Ab after diagnosis has not been investigated. This study analyzed the autoantibody response to ZnT8 in regard to age at onset and disease duration. Two new onset type 1 diabetes patient cohorts with different age distributions at onset (2-17 and 15-34 years of age at onset), a longitudinal subset of the younger type 1 diabetes patient cohort (n = 32), and a cohort of GAD65Ab-positive LADA patients (n = 47) was analyzed for the presence of autoantibodies directed to the two major isoforms, ZnT8-Arginine (ZnT8R) and ZnT8-Tryptophan (ZnT8W). The majority of type 1 diabetes patients tested positive for ZnT8Ab to both isoforms. ZnT8Ab titers were significantly higher in the younger type 1 diabetes patients as compared with the older cohort (ZnT8RAb at a median of 148 and 29 U/ml, respectively, p < 0.001) (ZnT8WAb at a median of 145 and 58 U/ml, respectively, p < 0.01). ZnT8RAb and ZnT8WAb titers were significantly lower in the LADA patients (ZnT8RAb at a median of 14 U/ml, ZnT8WAb at a median of 25 U/ml) as compared with either type 1 diabetes cohorts. In our longitudinal analysis of type 1 diabetes patients after clinical diagnosis, ZnT8Ab levels to both isoforms declined significantly during the initial year of disease (ZnT8RAb from a median of 320-162 U/ml, p = 0.0001; ZnT8WAb from a median of 128-46 U/ml, p = 0.0011). The antibody titers further declined during the following 4 years (p < 0.0001). We conclude that ZnT8Ab presents a useful marker for type 1 diabetes, especially in younger patients at disease diagnosis.

Conflict of interest statement

Declaration of interest: This study was performed as independent research sponsored by the National Institutes of Health(DK53456, DK53004, DK26190, and DK17047, a Basic Science Award from the American Diabetes Association to CSH, the EU 7th Framework Programme DIAPREPP (grant agreement 202013), the Swedish Research Council (2007–2266), and the Swedish Diabetes Association. The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.

Figures

Figure 1

ZnT8Ab titers to ZnT8R and ZnT8W correlate. Serum samples obtained from (a) 2–17-year-old and (b) 15–34-year-old new onset type 1 diabetes patients were tested for their binding to ZnT8R and ZnT8W. Antibody titers are shown as U/ml. R2 and p-values for r2 values are shown.

Figure 2

Overlapping prevalence of ZnT8Ab, GAD65Ab, and IA-2Ab at onset. Serum samples obtained from (a) 2–17-year-old and (b) 15–34-year-old new onset type 1 diabetes patients were tested for autoantibodies to ZnT8R and/or W (combined), GAD65, and IA-2. Frequencies of antibodies and their overlap with other autoantibodies are shown as percentage and total number of samples.

Figure 3

ZnT8Ab titers to both ZnT8 isoforms are significantly higher in the younger type 1 diabetes patient cohort. Serum samples obtained from 2–17-year-old (open symbols) and 15–34-year-old (black symbols) new onset type 1 diabetes patients, and LADA patients (gray symbols) were tested for their binding to ZnT8R (circles) and ZnT8W (squares). Median binding is indicated. Note that the ZnT8Ab titer is displayed on a logarithmic scale.

Figure 4

ZnT8Ab titers correlated with age at onset. Correlation between ZnT8RAb titers (a, b, c) and ZnT8WAb titers (d, e, f) with age at onset was tested in the 2–17-year-old cohort (a, d), the 15–34-year-old cohort (b, e), and the combined cohort (c, f). R2 and p-values for r2 values are shown.

Figure 5

Longitudinal titers of ZnT8Ab decline shortly after disease onset. Longitudinal samples from type 1 diabetes patients were obtained at onset, 1 and 5 years after onset. Samples were analyzed for (a) ZnT8RAb, (b) ZnT8WAb, (c) GAD65Ab, and (d) IA2Ab. Antibody-positive samples were analyzed for their respective antibody titer in respect to disease duration.