@article {783, title = {Disease-associated CTNNBL1 mutation impairs somatic hypermutation by decreasing nuclear AID.}, journal = {J Clin Invest}, volume = {130}, year = {2020}, month = {2020 08 03}, pages = {4411-4422}, abstract = {

Patients with common variable immunodeficiency associated with autoimmune cytopenia (CVID+AIC) generate few isotype-switched B cells with severely decreased frequencies of somatic hypermutations (SHMs), but their underlying molecular defects remain poorly characterized. We identified a CVID+AIC patient who displays a rare homozygous missense M466V mutation in β-catenin-like protein 1 (CTNNBL1). Because CTNNBL1 binds activation-induced cytidine deaminase (AID) that catalyzes SHM, we tested AID interactions with the CTNNBL1 M466V variant. We found that the M466V mutation interfered with the association of CTNNBL1 with AID, resulting in decreased AID in the nuclei of patient EBV-transformed B cell lines and of CTNNBL1 466V/V Ramos B cells engineered to express only CTNNBL1 M466V using CRISPR/Cas9 technology. As a consequence, the scarce IgG+ memory B cells from the CTNNBL1 466V/V patient showed a low SHM frequency that averaged 6.7 mutations compared with about 18 mutations per clone in healthy-donor counterparts. In addition, CTNNBL1 466V/V Ramos B cells displayed a decreased incidence of SHM that was reduced by half compared with parental WT Ramos B cells, demonstrating that the CTNNBL1 M466V mutation is responsible for defective SHM induction. We conclude that CTNNBL1 plays an important role in regulating AID-dependent antibody diversification in humans.

}, keywords = {Amino Acid Substitution, Apoptosis Regulatory Proteins, B-Lymphocytes, Cell Line, Child, Preschool, Common Variable Immunodeficiency, Cytidine Deaminase, Female, Homozygote, Humans, Immunologic Memory, Mutation, Missense, Nuclear Proteins, Somatic Hypermutation, Immunoglobulin}, issn = {1558-8238}, doi = {10.1172/JCI131297}, author = {Kuhny, Marcel and Forbes, Lisa R and {\c C}akan, Elif and Vega-Loza, Andrea and Kostiuk, Valentyna and Dinesh, Ravi K and Glauzy, Salom{\'e} and Stray-Pedersen, Asbjorg and Pezzi, Ashley E and Hanson, I Celine and Vargas-Hernandez, Alexander and Xu, Mina LuQuing and Coban-Akdemir, Zeynep H and Jhangiani, Shalini N and Muzny, Donna M and Gibbs, Richard A and Lupski, James R and Chinn, Ivan K and Schatz, David G and Orange, Jordan S and Meffre, Eric} } @article {72, title = {Loss of B Cells in Patients with Heterozygous Mutations in IKAROS.}, journal = {N Engl J Med}, volume = {374}, year = {2016}, month = {2016 Mar 17}, pages = {1032-1043}, abstract = {

BACKGROUND: Common variable immunodeficiency (CVID) is characterized by late-onset hypogammaglobulinemia in the absence of predisposing factors. The genetic cause is unknown in the majority of cases, and less than 10\% of patients have a family history of the disease. Most patients have normal numbers of B cells but lack plasma cells.

METHODS: We used whole-exome sequencing and array-based comparative genomic hybridization to evaluate a subset of patients with CVID and low B-cell numbers. Mutant proteins were analyzed for DNA binding with the use of an electrophoretic mobility-shift assay (EMSA) and confocal microscopy. Flow cytometry was used to analyze peripheral-blood lymphocytes and bone marrow aspirates.

RESULTS: Six different heterozygous mutations in IKZF1, the gene encoding the transcription factor IKAROS, were identified in 29 persons from six families. In two families, the mutation was a de novo event in the proband. All the mutations, four amino acid substitutions, an intragenic deletion, and a 4.7-Mb multigene deletion involved the DNA-binding domain of IKAROS. The proteins bearing missense mutations failed to bind target DNA sequences on EMSA and confocal microscopy; however, they did not inhibit the binding of wild-type IKAROS. Studies in family members showed progressive loss of B cells and serum immunoglobulins. Bone marrow aspirates in two patients had markedly decreased early B-cell precursors, but plasma cells were present. Acute lymphoblastic leukemia developed in 2 of the 29 patients.

CONCLUSIONS: Heterozygous mutations in the transcription factor IKAROS caused an autosomal dominant form of CVID that is associated with a striking decrease in B-cell numbers. (Funded by the National Institutes of Health and others.).

}, keywords = {Adolescent, Adult, Antigens, CD, B-Lymphocytes, Bone Marrow, Bone Marrow Examination, Child, Child, Preschool, Chromosomes, Human, Pair 7, Common Variable Immunodeficiency, Exome, Female, Heterozygote, Humans, Ikaros Transcription Factor, Immunoglobulin G, Lymphocyte Count, Male, Mutation, Pedigree, Sequence Analysis, DNA}, issn = {1533-4406}, doi = {10.1056/NEJMoa1512234}, author = {Kuehn, H S and Boisson, B and Cunningham-Rundles, C and Reichenbach, J and Stray-Pedersen, A and Gelfand, E W and Maffucci, P and Pierce, K R and Abbott, J K and Voelkerding, K V and South, S T and Augustine, N H and Bush, J S and Dolen, W K and Wray, B B and Itan, Y and Cobat, A and Sorte, H S and Ganesan, S and Prader, S and Martins, T B and Lawrence, M G and Orange, J S and Calvo, K R and Niemela, J E and Casanova, J-L and Fleisher, T A and Hill, H R and Kum{\'a}novics, A and Conley, M E and Rosenzweig, S D} }