Somatic mutations in VEXAS Syndrome and Erdheim-Chester disease: Inflammatory myeloid diseases.

Somatic mutations have been increasingly identified as etiologic for many hematologic and autoinflammatory disorders. VEXAS (vacuoles, E1 enzyme, X-linked, autoinflammatory, somatic) syndrome and Erdheim-Chester disease (ECD), a type of histiocytosis, can be classified as inflammatory myeloid diseases, characterized by systemic inflammation and multi-organ disease with predisposition to myeloid malignancies. VEXAS is a novel disease caused by UBA1 mutations that was first discovered using a genotype-driven approach (genotype was used to identify patients with undiagnosed inflammatory diseases). Since the initial description, many VEXAS cases have been reported and disease phenotype is expanding rapidly. In contrast, ECD was first characterized in the 1930s based on patients' phenotype, and only recently found to be caused by recurrent somatic mutations in the MAPK pathway (traditional phenotype-driven approach). The discovery of these mutations and development of target therapies have revolutionized the treatment of patients with histiocytosis, particularly ECD. Here we discuss the impact of causal and associated somatic mutations in VEXAS and ECD at both clinical and molecular levels.