@article {49, title = {Ataxia-Pancytopenia Syndrome Is Caused by Missense Mutations in SAMD9L.}, journal = {Am J Hum Genet}, volume = {98}, year = {2016}, month = {2016 Jun 02}, pages = {1146-1158}, abstract = {

Ataxia-pancytopenia (AP) syndrome is characterized by cerebellar ataxia, variable hematologic cytopenias, and predisposition to marrow failure and myeloid leukemia, sometimes associated with monosomy 7. Here, in the four-generation family UW-AP, linkage analysis revealed four regions that provided the maximal LOD scores possible, one of which was in a commonly microdeleted chromosome 7q region. Exome sequencing identified a missense mutation (c.2640C>A, p.His880Gln) in the sterile alpha motif domain containing 9-like gene (SAMD9L) that completely cosegregated with disease. By targeted sequencing of SAMD9L, we subsequently identified a different missense mutation (c.3587G>C, p.Cys1196Ser) in affected members of the first described family with AP syndrome, Li-AP. Neither variant is reported in the public databases, both affect highly conserved amino acid residues, and both are predicted to be damaging. With time in culture, lymphoblastic cell lines (LCLs) from two affected individuals in family UW-AP exhibited copy-neutral loss of heterozygosity for large portions of the long arm of chromosome 7, resulting in retention of only the wild-type SAMD9L allele. Newly established LCLs from both individuals demonstrated the same phenomenon. In addition, targeted capture and sequencing of SAMD9L in uncultured blood DNA from both individuals showed bias toward the wild-type allele. These observations indicate in~vivo hematopoietic mosaicism. The hematopoietic cytopenias that characterize AP syndrome and the selective advantage for clones that have lost the mutant allele support the postulated role of SAMD9L in the regulation of cell proliferation. Furthermore, we show that AP syndrome is distinct from the dyskeratoses congenita telomeropathies, with which it shares some clinical characteristics.

}, keywords = {Adolescent, Adult, Cerebellar Ataxia, Child, Chromosome Aberrations, Chromosomes, Human, Pair 7, Exome, Female, Genetic Linkage, Genotype, High-Throughput Nucleotide Sequencing, Humans, Intracellular Signaling Peptides and Proteins, Loss of Heterozygosity, Male, Middle Aged, Mutation, Missense, Pancytopenia, Pedigree, Proteins, Tumor Suppressor Proteins, Young Adult}, issn = {1537-6605}, doi = {10.1016/j.ajhg.2016.04.009}, author = {Chen, Dong-Hui and Below, Jennifer E and Shimamura, Akiko and Keel, Sioban B and Matsushita, Mark and Wolff, John and Sul, Youngmee and Bonkowski, Emily and Castella, Maria and Taniguchi, Toshiyasu and Nickerson, Deborah and Papayannopoulou, Thalia and Bird, Thomas D and Raskind, Wendy H} } @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} }