Diagnosis And Islet β-cell Function Of Latent Autoimmune Diabetes In Adults

Part 1 Carboxypeptidase-H Antibody Assay: Diagnostic Implications and Effects on Islet β -cell Function in Adult-onset Latent Autoimmune Diabetes (LADA)Objective: To establish a radioimmunoprecipitation assay for carboxypeptidase-H antibody (CPH-Ab), and explore its diagnostic role and effect of CPH-Ab on islet 3 -cell function in LADA.Design: Cross-sectional and case-contrul studies.Setting: Institute of Metabolism and Endocrinology, Xiangya 2nd Hospital, Central South University.Participants: Five hundred and forty-five type 2 diabetic patients (T2DM), 26 ~91yr. 85 type 1 diabetic patients (T1DM), 7~70yr. 123 healthy controls, 7~70yr.Methods: Human CPH cDNA plasmid was used in coupled in vitro transcription and translation system with methionine-free rabbit reticulocyte lysates in the presence of 35S-methionine. Serum CPH-Ab levels were determined by radioimmune assay, GAD-Ab assay as well for the T2DM group. T2DM patients, according to CPH-Ab and GAD-Ab status, were divided into CPH-Ab positive group, GAD-Ab positive group and antibody-negative group to compare their clinical characteristics and their relations with metabolic syndrome. The effect of CPH-Ab on islet β -cell function were evaluated by comparison of C-peptide in three T2DM groups.Main outcome measures: Prevalence of CPH-Ab, Body mass index (BMI), Blood pressure, Blood lipidemia (including serum triglyceride, total cholesterol, high density lipoprotein and low density lipoprotein), Fasting and postprandial 2?C-peptides.Results: Intra-assay CV and inter-assay CV of CPH-Ab assay were 4.9%~8.3% and7.1%~10.8%. The results were comparable with those of an international standardized laboratory (concordance was 97.5%). The prevalence of CPH-Ab in T2DM (5.5%, 30/545) was higher than that of T1DM patients(0%, 0/85; P < 0.05)and healthy controls(0.8%, 1/123; P<0.05) . Only 1/30 T2DM patients with CPH-Ab also had CPH-Ab. The positivity of CPH-Ab was higher in patients with lower body weight (BMI< 21kg/m2). The patients with CPH-Ab had a wider range of age at onset, lower body mass index and more tendency to develop ketosis. And these patients had lower levels of the markers of metabolic syndrome (including lower BMI, hypertension and serum triglyceride level) and higher prevalence of peripheral neuropathy. The fasting C-peptide level in CPH-Ab positive patients was between that of GAD-Ab positive patients and that of antibody-negative patients.Conclusions: (1)The CPH-Ab assay established in our laboratory is a stable and reproducible method for clinical applications. (2)CPH-Ab is a new autoimmune marker for the diagnosis of LAD A. (3)The clinical characteristics of patients with CPH-Ab are between that of classic LAD A who is GAD-Ab positive and antibody-negative T2DM patients. (4)The effect of CPH-Ab was less marked than that of GAD-Ab on islet β -cell function in LADA patients. (5)CPH-Ab screening should target the GAD-Ab negative T2DM patients in practice.