Validation of the IgA1 Detection Method With Gradient Glycosylation by Mass Spectrometry as a Potential Marker of Renal Involvement in Pediatric Rheumatoid Purpura

In this ancillary study on the FoxTreg cohort, the study investigators will select variables to input and thus develop two models (Linear Discriminant Analysis and Decision Tree). The aim of this study is to validate the method in terms of repeatability, reproducibility, control of pre-analytical conditions and sample conservation, to complete the screening of IgA glycosylation in individuals of the FoxTreg cohort and to refine the glycopeptide signature to predict renal involvement.