Rapid clinical deployment of UBA1 testing in patients with VEXAS syndrome.

Objective: VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) is a recently described autoinflammatory syndrome caused by pathogenic variants in UBA1. However, there is a dearth of widely available UBA1 testing aside from large, expensive sequencing studies. Thus, we sought to rapidly develop, validate, and clinically deploy a cost-effective assay for detecting the most common UBA1 variants.

Methods: We developed, validated, and implemented a single base extension mass spectrometry assay for detecting pathogenic UBA1 variants at the c.121, c.122, and c.118-1 positions in patients with suspected VEXAS syndrome. Assay performance characteristics were assessed using peripheral blood and bone marrow samples from patients with (n = 8) and without (n = 36) VEXAS.

Results: The assay demonstrated a lower limit of detection (LOD) of 10% variant allele fraction for each mutation. The analytical accuracy, sensitivity, and specificity were each demonstrated to be 100% at the LOD, with excellent intra- and interrun reproducibility. Based on literature review of reported UBA1 variants associated with VEXAS, to date, this assay detects the most prevalent variants, with a clinical sensitivity of 97% or more.

Conclusions: A cost-effective, mass spectrometry-based assay with high analytical and clinical performance can feasibly be implemented in hospital laboratories for diagnosis of VEXAS syndrome.