Gene CNVs and protein levels of complement C4A and C4B as novel biomarkers for partial disease remissions in new-onset type 1 diabetes patients

Objective To determine the roles of complement C4A and C4B gene copy-number variations and their plasma protein concentrations in residual insulin secretion and loss of pancreatic beta-cell function in new-onset type 1 diabetes (T1D) patients. Methods We studied 34 patients of European ancestry with new-onset T1D, aged between 3 and 17 yr (10.7 +/- 3.45), at Nationwide Children's Hospital in Columbus, Ohio. Gene copy-number and size variations of complement C4A and C4B were determined by genomic Southern blot analyses. C4A and C4B protein phenotypes were elucidated by immunofixation and radial immunodiffusion. Two-digit human leukocyte antigen (HLA)-DRB1 genotypes were determined by sequence-specific polymerase chain reaction. At 1- and 9-month post diagnosis, stimulated C-peptide levels were measured after a standardized mixed-meal tolerance test. Results The diploid gene copy-numbers of C4A varied from 0 to 4, and those of C4B from 0 to 3. Patients with higher copy-number of C4A or higher C4A plasma protein concentrations at diagnosis had higher C-peptide levels at 1-month post diagnosis (p = 0.008; p = 0.008). When controlled by the Z-score of body mass index, C4A copy-numbers, C4A protein concentrations, the age of disease onset, and the number of HLA-DR3 but not DR4 alleles were significant parameters in determining C-peptide levels. At 9-month post diagnosis, 42.3% of patients remained in partial remission, and these patients were characterized by lower total C4B copy-numbers or lower C4B protein concentrations (p = 0.02; p = 0.0004). Conclusions C4A appears to associate with the protection of residual beta-cell function in new-onset T1D; C4B is correlated with the end of disease remission at 9-month post diagnosis.