Wyatt R C, Brigatti C, Liberati D, Grace S L, Gillard B T, Long A E, Marzinotto I, Shoemark D K, Chandler K A, Achenbach P, Gillespie K M, Piemonti L, Lampasona V, Williams A J K
Diabetes and Metabolism, Translational Health Sciences, University of Bristol, Bristol, UK.
Diabetes Research Institute, Milan, Italy.
Diabet Med. 2018 Jul;35(7):954-963. doi: 10.1111/dme.13628. Epub 2018 Apr 19.
Glutamate decarboxylase (GAD) antibodies are the most widely used predictive marker for Type 1 diabetes, but many individuals currently found to be GAD antibody-positive are unlikely to develop diabetes. We have shown previously that radioimmunoassays using N-terminally truncated S-GAD (96-585) offer better disease specificity with similar sensitivity to full-length S-GAD (1-585). To determine whether assay performance could be improved further, we evaluated a more radically truncated S-GAD (143-585) radiolabel.
Samples from people with recent-onset Type 1 diabetes (n = 157) and their first-degree relatives (n = 745) from the Bart's-Oxford family study of childhood diabetes were measured for GAD antibodies using S-labelled GAD (143-585). These were screened previously using a local radioimmunoassay with S-GAD (1-585). A subset was also tested by enzyme-linked immunosorbent assay (ELISA), which performs well in international workshops, but requires 10 times more serum. Results were compared with GAD antibody measurements using S-GAD (1-585) and S-GAD (96-585).
Sensitivity of GAD antibody measurement was maintained using S-GAD (143-585) compared with S-GAD (1-585) and S-GAD (96-585). Specificity for Type 1 diabetes was improved compared with S-GAD (1-585), but was similar to S-GAD (96-585). Relatives found to be GAD antibody-positive using these truncated labels were at increased risk of diabetes progression within 15 years, compared with those positive for GAD(1-585) antibody only, and at similar risk to those found GAD antibody-positive by ELISA.
The first 142 amino acids of GAD do not contribute to epitopes recognized by Type 1 diabetes-associated GAD antibodies. Low-volume radioimmunoassays using N-terminally truncated S-GAD are more specific than those using full-length GAD and offer practical alternatives to the GAD antibody ELISA for identifying children at increased risk of Type 1 diabetes.
谷氨酸脱羧酶（GAD）抗体是1型糖尿病最常用的预测标志物，但目前发现许多GAD抗体呈阳性的个体不太可能患糖尿病。我们之前已经表明，使用N端截短的S-GAD（96-585）的放射免疫测定法在敏感性与全长S-GAD（1-585）相似的情况下具有更好的疾病特异性。为了确定检测性能是否可以进一步提高，我们评估了一种截短程度更大的S-GAD（143-585）放射性标记物。
使用S标记的GAD（143-585）对来自儿童糖尿病的巴特牛津家族研究中近期发病的1型糖尿病患者（n = 157）及其一级亲属（n = 745）的样本进行GAD抗体检测。这些样本之前使用S-GAD（1-585）的局部放射免疫测定法进行过筛查。还通过酶联免疫吸附测定法（ELISA）对一个子集进行了检测，ELISA在国际研讨会上表现良好，但所需血清量是前者的10倍。将结果与使用S-GAD（1-585）和S-GAD（96-585）进行的GAD抗体检测结果进行比较。
与S-GAD（1-585）和S-GAD（96-585）相比，使用S-GAD（143-585）时GAD抗体检测的敏感性得以保持。与S-GAD（1-585）相比，对1型糖尿病的特异性有所提高，但与S-GAD（96-585）相似。与仅GAD（1-585）抗体呈阳性的亲属相比，使用这些截短标记物检测发现GAD抗体呈阳性的亲属在15年内糖尿病进展的风险增加，且与ELISA检测发现GAD抗体呈阳性的亲属风险相似。
GAD的前142个氨基酸对1型糖尿病相关GAD抗体识别的表位没有贡献。使用N端截短的S-GAD的小体积放射免疫测定法比使用全长GAD的方法更具特异性，并且为识别1型糖尿病风险增加的儿童提供了替代GAD抗体ELISA的实用方法。
