Hemizygous Moesin (MSN) Gene Deletion in an Adult With Chronic Neutropenia

X-linked moesin-associated immunodeficiency (X-MAID) is a recently identified combined immunodeficiency caused by a mutation in the moesin (MSN) gene. It is characterized by cytopenias, hypogammaglobulinemia, poor immune response to vaccine antigens, and increased susceptibility to early-life infections. We report a patient with adult-onset neutropenia, lymphopenia, inadequate response to the pneumococcal polysaccharide vaccine (PPSV23), and recurrent bacterial infections associated with a hemizygous MSN deletion. Notably, the patient has no history of significant childhood infections, cytopenias, or hypogammaglobulinemia. Although only a few cases have been documented worldwide, we underscore the importance of whole-genome sequencing (WES) in diagnosing this atypical immunodeficiency disease in adulthood. Moreover, this report may shed light on our understanding of further variants of X-MAID and enrich the known spectrum of the disease.