Somatic mosaicism in genetic errors of immunity

Genetic mosaicism in somatic cells can lead to the presence of pathogenic variants in a subset of immune cells causing genetic errors of immunity, often phenocopying germline inborn errors of immunity. Over the last 2 decades, significant progress has been made in the identification of these disorders in patients, including discovery of new diseases. Diagnosis of disease-causing somatic mosaicism provides a target for treatment and monitoring of patients and has implications for genetic counseling. However, there continue to be barriers in the identification of somatic mosaicism, particularly for the clinical diagnosis of patients, based on the limitations of current diagnostic sequencing and analysis approaches. This review focuses on how somatic mosaicism can lead to genetic errors of immunity, the genes known to be associated with somatic genetic errors of immunity, and challenges in the field for accurate diagnosis of patients.