1 | Introduction
Hyper-immunoglobulin M (HIGM) syndrome is a rare (incidence: 1 in 100,000 births) primary immunodeficiency syndrome in which defective B-cell isotype switching leads to a phenotype characterized by low serum levels of IgG, IgA, and IgE or their complete absence and either normal or increased concentration of IgM. 1-4 This syndrome is known as the immunoglobulin class-switch recombination (Ig-CSR) deficiency. Mutations in a number of genes involved in CSR including CD40 ligand (CD40L ), CD40 , nuclear factor kappa-B essential modulator, inhibitor of kappa light-chain gene enhancer in B cells, alpha, nuclear factor kappa-B subunit 1, and activation-induced cytidine deaminase have been implicated in the development of HIGM. 2, 5, 6X-linked hyper-IgM (X-HIGM) syndrome, which is caused by CD40LG mutation, is the most common form of HIGM, accounting for approximately 65–70% of all cases. 7, 8
Clinical manifestations of XHIGM are complex and severe. Most patients are susceptible to opportunistic and recurrent infections that may be accompanied by autoimmune manifestations.9 This retrospective study on seven children diagnosed with XHIGM preliminarily assessed the clinical presentation and pathogens of respiratory infections in these patients and aimed to describe the respiratory infection characteristics of these patients. We also aimed to provide insights into the early diagnosis and target treatment strategies for respiratory infections in these children.