Clinical and immunological phenotypes of selective IgM deficiency in children: Results from a multicenter study

background: a few studies assessed the clinical and immunological features of selective IgM deficiency (SIgMD), especially in the pediatric age. we aimed to characterize the clinical and immunological phenotypes of a cohort of pediatric patients with SIgMD according to the different diagnostic criteria available. methods: In this multicenter study, we evaluated pediatric SIgMD patients diagnosed at the pediatric clinic in pavia, Italy, or through the Italian primary Immunodeficiency NETwork (IPINET) and monitored changes in their diagnosis over a time frame that ranges from several months to several years. results: forty-eight patients with SIgMD were included (mean serum IgM: 33 mg/dL). the most common clinical manifestations were recurrent infections (67%) and allergies (48%). subgroup analysis according to SIgMD definition criteria of the european society for Immunodeficiencies (ESID) showed no significant difference in clinical manifestations, also considering the group with additional immunological abnormalities. sixteen patients had long-term follow-up, during which 87% preserved their SIgMD diagnosis, while two patients showed a reduction in IgA in addition to low IgM. conclusions: our data suggest that the identification of a reduction in serum IgM in children should lead to a complete immunological work-up to obtain a comprehensive clinical and immunological characterization of the patient. the follow-up of these patients is fundamental to define the disease evolution and appropriate management.