title: Class switch recombination process in ataxia telangiectasia patients with elevated serum levels of IgM.
abstract: Ataxia telangiectasia (AT) is a rare primary immunodeficiency disorder with various clinical manifestations. Increased serum levels of IgM and recurrent infections, mainly sinopulmonary infections, can be the presenting feature in a number of AT patients and may be initially misdiagnosed as hyper-IgM (HIgM) syndrome. This study was designed to investigate class switch recombination (CSR) as a critical mechanism in B lymphocytes' maturation to produce different isotypes of antibody in response to antigen stimulation in AT cases with HIgM presentation. Quantitative IgE production after stimulation by IL-4 and CD40L was considered as an indicator for CSR function. We also compared their results with sex and age matched AT patients without HIgM presentation. We report four AT patients with recurrent infections during infancy and high serum levels of IgM. Laboratory evaluations revealed defective CSR while none of the three AT patients without HIgM presentation had a defect in the CSR process. The characterized defect in AT is a mutation in the ataxia telangiectasia mutated (ATM) gene. This gene may result in CSR defects due to impaired DNA break repair. A special association between AT and HIgM may indicate a new subgroup of AT patients according to their clinical phenotype and CSR condition.
authors.affiliation: a Research Center for Immunodeficiencies, Pediatrics Center of Excellence, Children's Medical Center , Tehran University of Medical Science , Tehran , Iran.
authors.forename: Payam
authors.initials: P
authors.lastname: Mohammadinejad
authors.forename: Hassan
authors.initials: H
authors.lastname: Abolhassani
authors.forename: Asghar
authors.initials: A
authors.lastname: Aghamohammadi
authors.forename: Shabnam
authors.initials: S
authors.lastname: Pourhamdi
authors.forename: Sujal
authors.initials: S
authors.lastname: Ghosh
authors.forename: Bamdad
authors.initials: B
authors.lastname: Sadeghi
authors.forename: Rasoul
authors.initials: R
authors.lastname: Nasiri Kalmarzi
authors.forename: Anne
authors.initials: A
authors.lastname: Durandy
authors.forename: Arndt
authors.initials: A
authors.lastname: Borkhardt
mesh_terms: D001260:Ataxia Telangiectasia / Q000235:genetics / Q000276:immunology*; D006801:Humans; D017578:Immunoglobulin Class Switching / Q000235:genetics / Q000276:immunology*; D007075:Immunoglobulin M / Q000097:blood* / Q000276:immunology; D009154:Mutation; D011995:Recombination, Genetic / Q000235:genetics / Q000276:immunology*
chemical_list: D007075:Immunoglobulin M
keywords: ataxia telangiectasia; class switch recombination; hyper-IgM syndrome; α-feto protein