Blood transcriptome indicates different disease etiology in pediatric ANCA-associated vasculitis subtypes.

Purpose: The goal of this study was to compare gene expression profiles from whole blood RNA-Seq data from pediatric ANCA-associated vasculitis patients to identify mechanistic endotypes. Methods: Whole blood mRNA profiles were generated from pediatric and adult vasculitis patients using Illumina GAIIx or Hi Seq 2500 RNA-Seq. Fastq files were alinged to human genome version GRC38.91 using STAR v2.6 and count data was generated with HTSEQ v0.61p1. Counts that passed quality and minimum expression filteres were anlayzed by hierarchical clustering based on Euclidean distance, and then for differential expression with DESeq2. Results: Our workflow identified 14,156 transcripts consistently expressed in vasculitis patients. Distance hierarchcial clustering identified three groups within these pediatric samples, and two groups plus one outlier in the adult samples. The two largest pediatric clusters were used as groups for differential expression analysis with the DESeq2 package for R. DE analysis identified 3,809 differentially expressed genes between clusters. Between the two adult groups, 1,682 genes were differentially expressed. DE genes were anlayzed for enrichment using ReatomePA as the reference database. This analysis revealed that genes involved in T-cell mediated immunity are more highly expressed in pediatric patients that fell into one endotype and those involved in neutrophil and Toll-like receptor mediated inflammation are more highly expressed in pediatric patients that fell into the other endotype group. Similar results were also seen in adults. Conclusions: This study utilizes RNA-Seq data to investigate the etiologies of ANCA-associated vasculitis. Using this approach we have identified T-cell mediated immunity and Toll-like receptor mediated inflammation as potentially differing inflammatory mechanisms in both pediatric and adult vasculitis patients that do not fall along normal diagnostic criteria. Whole blood mRNA expression profiles generated from pediatric vasculitis patients using RNA-Seq.