title: De novo mutation in the BTK gene of atypical X-linked agammaglobulinemia in a patient with recurrent pyoderma.
abstract: BACKGROUND
  X-linked agammaglobulinemia (XLA), characterized by a profound deficiency of all immunoglobulins and the absence of mature B cells, is caused by mutations in the gene encoding Bruton tyrosine kinase (BTK). Most patients have recurrent sinopulmonary infection. Infections usually occur in multiple locations across time, but single infection may be limited to one anatomic location.
  
  
  OBJECTIVE
  To report a case of atypical XLA with recurrent pyoderma and to observe the immunologic changes in the patient in 10 years.
  
  
  METHODS
  Immunologic investigations, skin wound culture, and molecular study with DNA sequencing were performed.
  
  
  RESULTS
  The patient was originally diagnosed as having common variable immunodeficiency disease because of the presence of circulating B cells (CD19+ B cells: 7%) at 11 years old. On further evaluation at the age of 20 years, flow cytometric analysis of lymphocytes showed only 0.4% B cells. The molecular study with DNA sequencing of the patient showed a point mutation in complementary DNA 1630 A>G(p.R544G) in the BTK gene, indicating that the patient has XLA. The mutation analysis of the BTK gene revealed a normal DNA sequence in the other family members.
  
  
  CONCLUSIONS
  This case is an important example of a possible presentation of XLA with a predominant skin manifestation, and it demonstrates that maintaining a high level of clinical suspicion is essential for the diagnosis of XLA in a child with recurrent pyoderma.
authors.affiliation: Section of Pediatric Allergy and Immunology, Department of Pediatrics, Mackay Memorial Hospital, Taipei, Taiwan.
authors.forename: Mao-Tsair
authors.initials: MT
authors.lastname: Lin
authors.forename: Yin-Hsiu
authors.initials: YH
authors.lastname: Chien
authors.forename: Shyh-Dar
authors.initials: SD
authors.lastname: Shyur
authors.forename: Li-Hsin
authors.initials: LH
authors.lastname: Huang
authors.forename: Yi-Chi
authors.initials: YC
authors.lastname: Chiang
authors.forename: Da-Chin
authors.initials: DC
authors.lastname: Wen
authors.forename: Pei-Hsuan
authors.initials: PH
authors.lastname: Liang
authors.forename: Hwai-Chih
authors.initials: HC
authors.lastname: Yang
mesh_terms: D000293:Adolescent; D000328:Adult; D000077329:Agammaglobulinaemia Tyrosine Kinase; D000361:Agammaglobulinemia / Q000150:complications / Q000235:genetics / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology; D001483:Base Sequence; D002648:Child; D017074:Common Variable Immunodeficiency / Q000473:pathology; D004252:DNA Mutational Analysis; D003937:Diagnosis, Differential; D005434:Flow Cytometry; D040181:Genetic Diseases, X-Linked / Q000150:complications / Q000235:genetics / Q000276:immunology*; D006801:Humans; D008297:Male; D010375:Pedigree; D017354:Point Mutation / Q000235:genetics*; D016133:Polymerase Chain Reaction; D011505:Protein-Tyrosine Kinases / Q000235:genetics*; D011711:Pyoderma / Q000209:etiology*; D012008:Recurrence
chemical_list: D011505:Protein-Tyrosine Kinases; D000077329:Agammaglobulinaemia Tyrosine Kinase; C000625949:BTK protein, human