title: Novel RAG1 mutation in a case of severe combined immunodeficiency.
abstract: OBJECTIVE
  The recombination activating enzymes RAG1 and RAG2 are essential to the process of V(D)J rearrangement in B and T cells and thus to the development of normal immune function. Mutations in RAG1 or RAG2 can lead to a spectrum of disorders, ranging from typical (B-)(T-) severe combined immunodeficiency to Omenn's syndrome. We present a unique presentation of RAG1 deficiency.
  
  
  METHODS
  We report on a 6-month-old girl who presented with severe respiratory distress, which continued to progress despite antibiotic therapy but seemed to respond to treatment with corticosteroids. The patient exhibited no erythroderma or eosinophilia, and her lymphoid organs were not enlarged.
  
  
  RESULTS
  Investigation of the immune system showed normal numbers of CD3+ T cells, which expressed either CD4 or CD8. Subsequent analysis of the T-cell receptor demonstrated that nearly all CD3+ T cells were clonal; one clone expressed CD4, whereas the other expressed CD8. The extremely restricted T-cell repertoire and the lack of circulating B cells prompted analysis of the RAG1 gene, which revealed a novel homozygous thymine to cytosine substitution at nucleotide position 2686.
  
  
  CONCLUSIONS
  This case underscores the importance of more extensive evaluation of the immune system even when widely available, standard, flow cytometric analysis shows normal numbers of T cells that express CD4 or CD8, especially in the absence of circulating B cells.
authors.affiliation: Division of Immunology and Allergy, Hospital for Sick Children, University of Toronto, Toronto, Canada.
authors.forename: Junyan
authors.initials: J
authors.lastname: Zhang
authors.forename: Linda
authors.initials: L
authors.lastname: Quintal
authors.forename: Adelle
authors.initials: A
authors.lastname: Atkinson
authors.forename: Brent
authors.initials: B
authors.lastname: Williams
authors.forename: Eyal
authors.initials: E
authors.lastname: Grunebaum
authors.forename: Chaim M
authors.initials: CM
authors.lastname: Roifman
mesh_terms: D019943:Amino Acid Substitution; D016175:B-Lymphocyte Subsets; D005260:Female; D016654:Genes, RAG-1 / Q000235:genetics*; D006801:Humans; D007223:Infant; D020125:Mutation, Missense; D017354:Point Mutation; D016511:Severe Combined Immunodeficiency / Q000175:diagnosis / Q000235:genetics*; D016176:T-Lymphocyte Subsets; D013601:T-Lymphocytes / Q000276:immunology