Thriving Without Transplant: A Case of X-Linked Hyper-IgM Syndrome with Near-Normal Quality of Life on IVIG

Introduction Hyper-IgM syndrome (HIGM) is a rare primary immunodeficiency characterized by impaired immunoglobulin class-switch recombination, most commonly due to mutations in the CD40 ligand (CD40L) gene. Affected patients typically present in early childhood with recurrent sinopulmonary infections and are at risk for opportunistic infections, chronic lung disease, and immune dysregulation. Hematopoietic stem cell transplantation (HSCT) is considered curative but carries significant risks. Long-term outcomes with immunoglobulin replacement therapy alone in selected patients remain an area of clinical interest. Case Report We present a male patient with X-linked HIGM (CD40L Thr254Met mutation) diagnosed at age 6 years. He initially developed recurrent otitis media by 1 year of age, followed by recurrent bacterial pneumonias and chronic sinusitis. Notably, he had no history of opportunistic infections. Initial immunologic evaluation revealed elevated IgM (431 mg/dL), markedly low IgG and IgA, and undetectable IgE levels. He was started on intravenous immunoglobulin (IVIG) replacement therapy in 2011, resulting in significant clinical improvement and resolution of recurrent infections. He is currently 21 years of age, his immunoglobulin levels demonstrated therapeutic IgG (1,542 mg/dL), persistently low IgA (<5 mg/dL), and improved IgM (170 mg/dL). Over the subsequent years, he experienced only two mild, self-limited upper respiratory infections and was described by his family as healthier than most peers. He remained compliant with IVIG therapy (30 g every 3 weeks) and reported excellent quality of life. A minor gastrointestinal concern consisting of intermittent passage of small amounts of mucus-like stool with flatus was reported but was infrequent, nonprogressive, and without systemic symptoms. Physical examination was unremarkable. Given his stable clinical course, lack of opportunistic infections, and excellent response to IVIG, HSCT was previously discussed but deferred in favor of continued immunoglobulin replacement. Discussion This case highlights the potential for excellent long-term clinical stability in selected patients with X-linked HIGM managed with IVIG alone. While HSCT remains the definitive therapy, careful patient selection is critical, particularly in those with mild phenotypes and excellent infection control. This case supports an individualized approach to management, emphasizing quality of life, treatment response, and shared decision-making in rare primary immunodeficiencies.