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    An Antibody-Deficiency Syndrome Due to Mutations in the CD19 Gene
    (Massachusetts Medical Soc, 2006) Van Zelm, Menno C.; Reisli, İsmail; Van Der Burg, Mirjam; Castano, Diana; Van Noesel, Carel J. M.; Van Tol, Maarten J. D.; Woellner, Cristina; Grimbacher, Bodo; Patino, Pablo J.; Van Dongen, Jasques J. M.; Franco, Jose L.
    BACKGROUND: The CD19 protein forms a complex with CD21, CD81, and CD225 in the membrane of mature B cells. Together with the B-cell antigen receptor, this complex signals the B cell to decrease its threshold for activation by the antigen. METHODS: We evaluated four patients from two unrelated families who had increased susceptibility to infection, hypogammaglobulinemia, and normal numbers of mature B cells in blood. We found a mutation in the CD19 gene in all four patients. The CD19 gene in the patients and their first-degree relatives was sequenced, and flow-cytometric immunophenotyping of B cells, immunohistochemical staining of lymphoid tissues, and DNA and messenger RNA analysis were performed. B-cell responses on the triggering of the B-cell receptor were investigated by in vitro stimulation; the antibody response after vaccination with rabies vaccine was also studied. RESULTS: All four patients had homozygous mutations in the CD19 gene. Levels of CD19 were undetectable in one patient and substantially decreased in the other three. Levels of CD21 were decreased, whereas levels of CD81 and CD225 were normal, in all four patients. The composition of the precursor B-cell compartment in bone marrow and the total numbers of B cells in blood were normal. However, the numbers of CD27+ memory B cells and CD5+ B cells were decreased. Secondary follicles in lymphoid tissues were small to normal in size and had a normal cellular composition. The few B cells that showed molecular signs of switching from one immunoglobulin class to another contained V-H-C-alpha and V-H-C-gamma transcripts with somatic mutations. The response of the patients' B cells to in vitro stimulation through the B-cell receptor was impaired, and in all four patients, the antibody response to rabies vaccination was poor. CONCLUSIONS: Mutation of the CD19 gene causes a type of hypogammaglobulinemia in which the response of mature B cells to antigenic stimulation is defective.
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    Large deletions and point mutations involving the dedicator of cytokinesis 8 (DOCK8) in the autosomal-recessive form of hyper-IgE syndrome
    (MOSBY-ELSEVIER, 2009) Engelhardt, Karin R.; McGhee, Sean; Winkler, Sabine; Sassi, Atfa; Woellner, Cristina; Lopez-Herrera, Gabriela; Chen, Andrew
    Background: The genetic etiologies of the hyper-IgE syndromes are diverse. Approximately 60% to 70% of patients with hyper-IgE syndrome have dominant mutations in STAT3, and a single patient was reported to have a homozygous TYK2 mutation. In the remaining patients with hyper-IgE syndrome, the genetic etiology has not yet been identified. Objectives: We aimed to identify a gene that is mutated or deleted in autosomal recessive hyper-IgE syndrome. Methods: We performed genome-wide single nucleotide polymorphism analysis for 9 patients with autosomal-recessive hyper-IgE syndrome to locate copy number variations and homozygous haplotypes. Homozygosity mapping was performed with 12 patients from 7 additional families. The candidate gene was analyzed by genomic and cDNA sequencing to identify causative alleles in a total of 27 patients with autosomal-recessive hyper-IgE syndrome. Results: Subtelomeric biallelic microdeletions were identified in 5 patients at the terminus of chromosome 9p. In all 5 patients, the deleted interval involved dedicator of cytokinesis 8 (DOCK8), encoding a protein implicated in the regulation of the actin cytoskeleton. Sequencing of patients without large deletions revealed 16 patients from 9 unrelated families with distinct homozygous mutations in DOCK8 causing premature termination, frameshift, splice site disruption, and single exon deletions and microdeletions. DOCK8 deficiency was associated with impaired activation of CD4(+) and CD8(+)T cells. Conclusion: Autosomal-recessive mutations in DOCK8 are responsible for many, although not all, cases of wautosomal-recessive hyper-IgE syndrome. DOCK8 disruption is associated with a phenotype of severe cellular immunodeficiency characterized by susceptibility to viral infections, atopic eczema, defective T-cell activation and T(H)17 cell differentiation, and impaired eosinophil homeostasis and dysregulation of IgE. (J Allergy Clin Immunol 2009;124:1289-302.)