Abstract: Objective　To analyze the clinical features of X-linked agammaglobulinemia (XLA) and the gene mutation of Bruton tyrosine kinase (BTK). Method　The clinical data of 20 children with XLA confirmed by genetic testing were retrospectively analyzed, and the mutation of BTK gene was analyzed by Sanger sequencing. Results　All the 20 cases were male, and the age at onset was from 6 to 54 months, and an average age was 26.3±14.61 months. The age at gene diagnosis was from 26 to 168 months and an average age was 64.7±38.22 months. The median diagnostic period was 27.5 months (3~114 months). Respiratory tract infection was the main clinical manifestation of all cases: 18 cases were diagnosed of pneumonia and the other 2 cases were diagnosed of digestive tract infection. Immune function test showed that either mature B lymphocytes were absent or the proportion of mature B lymphocytes was significantly reduced, and serum IgG, IgA and IgM levels were significantly reduced. Gene detection revealed 10 missense mutations, 4 nonsense mutations, 3 frameshift mutations, 2 intron shear site mutation and 1 splicing mutation. Twenty patients were received intravenous gamma globulin replacement therapy after the diagnosis, and the frequency of infection was significantly reduced without sequelae. Conclusion　For boys with recurrent severe and special site infection, especially those with related family history, immune function screening should be performed as soon as possible, along with genetic testing, for clear diagnosis and genetic counseling.

Key words: X-linked agammaglobulinemia;　Bruton tyrosine kinase;　immunologic deficiency