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Thomson DW, Shahrin NH, Wang PPS, Wadham C, Shanmuganathan N, Scott HS, Dinger ME, Hughes TP, Schreiber AW, Branford S. Aberrant RAG-mediated recombination contributes to multiple structural rearrangements in lymphoid blast crisis of chronic myeloid leukemia. Leukemia 2020; 34:2051-2063. [PMID: 32076119 DOI: 10.1038/s41375-020-0751-y] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2019] [Revised: 01/08/2020] [Accepted: 02/06/2020] [Indexed: 11/10/2022]
Abstract
Blast crisis of chronic myeloid leukemia is associated with poor survival and the accumulation of genomic lesions. Using whole-exome and/or RNA sequencing of patients at chronic phase (CP, n = 49), myeloid blast crisis (MBC, n = 19), and lymphoid blast crisis (LBC, n = 20), we found 25 focal gene deletions and 14 fusions in 24 patients in BC. Deletions predominated in LBC (83% of structural variants). Transcriptional analysis identified the upregulation of genes involved in V(D)J recombination, including RAG1/2 and DNTT in LBC. RAG recombination is a reported mediator of IKZF1 deletion. We investigated the extent of RAG-mediated genomic lesions in BC. Molecular hallmarks of RAG activity; DNTT-mediated nucleotide insertions and a RAG-binding motif at structural variants were exclusively found in patients with high RAG expression. Structural variants in 65% of patients in LBC displayed these hallmarks compared with only 5% in MBC. RAG-mediated events included focal deletion and novel fusion of genes associated with hematologic cancer: IKZF1, RUNX1, CDKN2A/B, and RB1. Importantly, 8/8 patients with elevated DNTT at CP diagnosis progressed to LBC by 12 months, potentially enabling early prediction of LBC. This work confirms the central mutagenic role of RAG in LBC and describes potential clinical utility in CML management.
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Affiliation(s)
- Daniel W Thomson
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
| | - Nur Hezrin Shahrin
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
| | - Paul P S Wang
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
- Australian Cancer Research Foundation Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
| | - Carol Wadham
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
| | - Naranie Shanmuganathan
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
- School of Medicine, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, SA, Australia
- South Australian Health and Medical Research Institute, Adelaide, SA, Australia
| | - Hamish S Scott
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
- Australian Cancer Research Foundation Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Medicine, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, SA, Australia
| | - Marcel E Dinger
- School of Biotechnology and Biomolecular Sciences, University of New South Wales, Kensington Campus, Sydney, NSW, Australia
| | - Timothy P Hughes
- School of Medicine, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, SA, Australia
- South Australian Health and Medical Research Institute, Adelaide, SA, Australia
| | - Andreas W Schreiber
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia
- Australian Cancer Research Foundation Genomics Facility, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia
- School of Biological Sciences, University of Adelaide, Adelaide, SA, Australia
| | - Susan Branford
- Department of Genetics and Molecular Pathology, Centre for Cancer Biology, SA Pathology, Adelaide, SA, Australia.
- School of Pharmacy and Medical Science, Division of Health Sciences, University of South Australia, Adelaide, SA, Australia.
- School of Medicine, Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, SA, Australia.
- School of Biological Sciences, University of Adelaide, Adelaide, SA, Australia.
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Abstract
Potential ionising radiation exposure scenarios are varied, but all bring risks beyond the simple issues of short-term survival. Whether accidentally exposed to a single, whole-body dose in an act of terrorism or purposefully exposed to fractionated doses as part of a therapeutic regimen, radiation exposure carries the consequence of elevated cancer risk. The long-term impact of both intentional and unintentional exposure could potentially be mitigated by treatments specifically developed to limit the mutations and precancerous replication that ensue in the wake of irradiation The development of such agents would undoubtedly require a substantial degree of in vitro testing, but in order to accurately recapitulate the complex process of radiation-induced carcinogenesis, well-understood animal models are necessary. Inbred strains of the laboratory mouse, Mus musculus, present the most logical choice due to the high number of molecular and physiological similarities they share with humans. Their small size, high rate of breeding and fully sequenced genome further increase its value for use in cancer research. This chapter will review relevant m. musculus inbred and F1 hybrid animals of radiation-induced myeloid leukemia, thymic lymphoma, breast and lung cancers. Method of cancer induction and associated molecular pathologies will also be described for each model.
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PTEN microdeletions in T-cell acute lymphoblastic leukemia are caused by illegitimate RAG-mediated recombination events. Blood 2014; 124:567-78. [PMID: 24904117 DOI: 10.1182/blood-2014-03-562751] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Phosphatase and tensin homolog (PTEN)-inactivating mutations and/or deletions are an independent risk factor for relapse of T-cell acute lymphoblastic leukemia (T-ALL) patients treated on Dutch Childhood Oncology Group or German Cooperative Study Group for Childhood Acute Lymphoblastic Leukemia protocols. Some monoallelic mutated or PTEN wild-type patients lack PTEN protein, implying that additional PTEN inactivation mechanisms exist. We show that PTEN is inactivated by small deletions affecting a few exons in 8% of pediatric T-ALL patients. These microdeletions were clonal in 3% and subclonal in 5% of patients. Conserved deletion breakpoints are flanked by cryptic recombination signal sequences (cRSSs) and frequently have non-template-derived nucleotides inserted in between breakpoints, pointing to an illegitimate RAG recombination-driven activity. Identified cRSSs drive RAG-dependent recombination in a reporter system as efficiently as bona fide RSSs that flank gene segments of the T-cell receptor locus. Remarkably, equivalent microdeletions were detected in thymocytes of healthy individuals. Microdeletions strongly associate with the TALLMO subtype characterized by TAL1 or LMO2 rearrangements. Primary and secondary xenotransplantation of TAL1-rearranged leukemia allowed development of leukemic subclones with newly acquired PTEN microdeletions. Ongoing RAG activity may therefore actively contribute to the acquisition of preleukemic hits, clonal diversification, and disease progression.
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Mouse models for efficacy testing of agents against radiation carcinogenesis—a literature review. INTERNATIONAL JOURNAL OF ENVIRONMENTAL RESEARCH AND PUBLIC HEALTH 2012; 10:107-43. [PMID: 23271302 PMCID: PMC3564133 DOI: 10.3390/ijerph10010107] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Revised: 11/26/2012] [Accepted: 12/11/2012] [Indexed: 12/12/2022]
Abstract
As the number of cancer survivors treated with radiation as a part of their therapy regimen is constantly increasing, so is concern about radiation-induced cancers. This increases the need for therapeutic and mitigating agents against secondary neoplasias. Development and efficacy testing of these agents requires not only extensive in vitro assessment, but also a set of reliable animal models of radiation-induced carcinogenesis. The laboratory mouse (Mus musculus) remains one of the best animal model systems for cancer research due to its molecular and physiological similarities to man, small size, ease of breeding in captivity and a fully sequenced genome. This work reviews relevant M. musculus inbred and F1 hybrid animal models and methodologies of induction of radiation-induced leukemia, thymic lymphoma, breast, and lung cancer in these models. Where available, the associated molecular pathologies are also included.
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Arnal SM, Holub AJ, Salus SS, Roth DB. Non-consensus heptamer sequences destabilize the RAG post-cleavage complex, making ends available to alternative DNA repair pathways. Nucleic Acids Res 2010; 38:2944-54. [PMID: 20139091 PMCID: PMC2875030 DOI: 10.1093/nar/gkp1252] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
V(D)J recombination entails double-stranded DNA cleavage at the antigen receptor loci by the RAG1/2 proteins, which recognize conserved recombination signal sequences (RSSs) adjoining variable (V), diversity (D) and joining (J) gene segments. After cleavage, RAG1/2 remain associated with the coding and signal ends (SE) in a post-cleavage complex (PCC), which is critical for their proper joining by classical non-homologous end joining (NHEJ). Certain mutations in RAG1/2 destabilize the PCC, allowing DNA ends to access inappropriate repair pathways such as alternative NHEJ, an error-prone pathway implicated in chromosomal translocations. The PCC is thus thought to discourage aberrant rearrangements by controlling repair pathway choice. Since interactions between RAG1/2 and the RSS heptamer element are especially important in forming the RAG-SE complex, we hypothesized that non-consensus heptamer sequences might affect PCC stability. We find that certain non-consensus heptamers, including a cryptic heptamer implicated in oncogenic chromosomal rearrangements, destabilize the PCC, allowing coding and SEs to be repaired by non-standard pathways, including alternative NHEJ. These data suggest that some non-consensus RSS, frequently present at chromosomal translocations in lymphoid neoplasms, may promote genomic instability by a novel mechanism, disabling the PCC’s ability to restrict repair pathway choice.
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Affiliation(s)
- Suzzette M Arnal
- Department of Pathology, New York University School of Medicine, New York, NY 10016, USA
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The t(14;18)(q32;q21)/IGH-MALT1 translocation in MALT lymphomas contains templated nucleotide insertions and a major breakpoint region similar to follicular and mantle cell lymphoma. Blood 2009; 115:2214-9. [PMID: 19965626 DOI: 10.1182/blood-2009-08-236265] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The t(14;18)(q32;q21) involving the immunoglobulin heavy chain locus (IGH) and the MALT1 gene is a recurrent abnormality in mucosa-associated lymphoid tissue (MALT) lymphomas. However, the nucleotide sequence of only one t(14;18)-positive MALT lymphoma has been reported so far. We here report the molecular characterization of the IGH-MALT1 fusion products in 5 new cases of t(14;18)-positive MALT lymphomas. Similar to the IGH-associated translocations in follicular and mantle cell lymphomas, the IGH-MALT1 junctions in MALT lymphoma showed all features of a recombination signal sequence-guided V(D)J-mediated translocation at the IGH locus. Furthermore, analogous to follicular and mantle cell lymphoma, templated nucleotides (T-nucleotides) were identified at the t(14;18)/IGH-MALT1 breakpoint junctions. On chromosome 18, we identified a novel major breakpoint region in MALT1 upstream of its coding region. Moreover, the presence of duplications of MALT1 nucleotides in one case suggests an underlying staggered DNA-break process not consistent with V(D)J-mediated recombination. The molecular characteristics of the t(14;18)/IGH-MALT1 resemble those found in the t(14;18)/IGH-BCL2 in follicular lymphoma and t(11;14)/CCND1-IGH in mantle cell lymphoma, suggesting that these translocations could be generated by common pathomechanisms involving illegitimate V(D)J-mediated recombination on IGH as well as new synthesis of T-nucleotides and nonhomologous end joining (NHEJ) or alternative NHEJ repair pathways on the IGH-translocation partner.
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Krzywinski M, Schein J, Birol I, Connors J, Gascoyne R, Horsman D, Jones SJ, Marra MA. Circos: an information aesthetic for comparative genomics. Genome Res 2009; 19:1639-45. [PMID: 19541911 DOI: 10.1101/gr.092759.109] [Citation(s) in RCA: 7019] [Impact Index Per Article: 467.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
We created a visualization tool called Circos to facilitate the identification and analysis of similarities and differences arising from comparisons of genomes. Our tool is effective in displaying variation in genome structure and, generally, any other kind of positional relationships between genomic intervals. Such data are routinely produced by sequence alignments, hybridization arrays, genome mapping, and genotyping studies. Circos uses a circular ideogram layout to facilitate the display of relationships between pairs of positions by the use of ribbons, which encode the position, size, and orientation of related genomic elements. Circos is capable of displaying data as scatter, line, and histogram plots, heat maps, tiles, connectors, and text. Bitmap or vector images can be created from GFF-style data inputs and hierarchical configuration files, which can be easily generated by automated tools, making Circos suitable for rapid deployment in data analysis and reporting pipelines.
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Affiliation(s)
- Martin Krzywinski
- Canada's Michael Smith Genome Sciences Center, Vancouver, British Columbia V5Z 4S6, Canada.
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Finette BA. Analysis of mutagenic V(D)J recombinase mediated mutations at the HPRT locus as an in vivo model for studying rearrangements with leukemogenic potential in children. DNA Repair (Amst) 2006; 5:1049-64. [PMID: 16807138 DOI: 10.1016/j.dnarep.2006.05.023] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Pediatric acute lymphocytic leukemia (ALL) is a multifactorial malignancy with many distinctive developmentally specific features that include age specific acquisition of deletions, insertions and chromosomal translocations. The analysis of breakpoint regions involved in these leukemogenic genomic rearrangements has provided evidence that many are the consequence of V(D)J recombinase mediated events at both immune and non-immune loci. Hence, the direct investigation of in vivo genetic and epigenetic features in human peripheral lymphocytes is necessary to fully understand the mechanisms responsible for the specificity and frequency of these leukemogenic non-immune V(D)J recombinase events. In this review, I will present the utility of analyzing mutagenic V(D)J recombinase mediated genomic rearrangements at the HPRT locus in humans as an in vivo model system for understanding the mechanisms responsible for leukemogenic genetic alterations observed in children with leukemia.
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Affiliation(s)
- Barry A Finette
- Department of Pediatrics, Microbiology and Molecular Genetics, University of Vermont College of Medicine, E203 Given Building, 89 Beaumont Ave., Burlington, VT 05405, USA.
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Marculescu R, Vanura K, Montpellier B, Roulland S, Le T, Navarro JM, Jäger U, McBlane F, Nadel B. Recombinase, chromosomal translocations and lymphoid neoplasia: targeting mistakes and repair failures. DNA Repair (Amst) 2006; 5:1246-58. [PMID: 16798110 DOI: 10.1016/j.dnarep.2006.05.015] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
A large number of lymphoid malignancies is characterized by specific chromosomal translocations, which are closely linked to the initial steps of pathogenesis. The hallmark of these translocations is the ectopic activation of a silent proto-oncogene through its relocation at the vicinity of an active regulatory element. Due to the unique feature of lymphoid cells to somatically rearrange and mutate receptor genes, and to the corresponding strong activity of the immune enhancers/promoters at that stage of cell development, B- and T-cell differentiation pathways represent propitious targets for chromosomal translocations and oncogene activation. Recent progress in the understanding of the V(D)J recombination process has allowed a more accurate definition of the translocation mechanisms involved, and has revealed that V(D)J-mediated translocations result both from targeting mistakes of the recombinase, and from illegitimate repair of the V(D)J recombination intermediates. Surprisingly, V(D)J-mediated translocations turn out to be restricted to two specific sub-types of lymphoid malignancies, T-cell acute lymphoblastic leukemias, and a restricted set of mature B-cell Non-Hodgkin's lymphomas.
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Affiliation(s)
- Rodrig Marculescu
- Department of Internal Medicine I, Division of Hematology, Medical University of Vienna, Währinger Gürtel 18-20, A-1090 Vienna, Austria
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Hardianti MS, Tatsumi E, Syampurnawati M, Furuta K, Suzuki A, Saigo K, Kawano S, Takenokuchi M, Kumagai S, Matsuo Y, Koizumi T, Takeuchi M. Presence of somatic hypermutation and activation-induced cytidine deaminase in acute lymphoblastic leukemia L2 with t(14;18)(q32;q21). Eur J Haematol 2005; 74:11-9. [PMID: 15613101 DOI: 10.1111/j.1600-0609.2004.00338.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
AIM Acute lymphoblastic leukemia (ALL) with L2 (FAB) morphology has rarely been reported to show t(14;18)(q32;q21). We aimed to delineate the stage at which this type of ALL is derived in B-lineage differentiation. METHODS The somatic hypermutation (SHM) of the variable region of immunoglobulin heavy chain (IgV(H)) gene and the expression of terminal deoxynucleotidyl transferase (TdT), recombination-activating gene 1 and 2 (RAG-1 and -2), and activation-induced cytidine deaminase (AID) were investigated in three cell lines and two fresh samples, including a pair of matched fresh and cell line cells. RESULTS TdT, RAG-1, and RAG-2 were variably expressed. AID was expressed in four of five samples. SHM of the IgV(H) gene was found in all samples with high average frequency (11.84%) comparable with that in follicular lymphoma. Ongoing mutation was seen in two fresh samples. CONCLUSION As AID and SHM are generally regarded as properties exhibited by mature B cells, the presence of AID and SHM in this study seems to be incompatible with the general understanding of the early stage derivation of ALL in B-lineage differentiation. The results here give some insight into the relationship between disease type (ALL or lymphoma) and derivation stage, the overlapping of the early stage phenotype and the mature genomic characteristics, and the probable relationship between the mechanism of the occurrence of t(14;18)(q32;q21) and the machinery causing SHM.
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MESH Headings
- Base Sequence
- Cell Line, Tumor
- Chromosomes, Human, Pair 14/genetics
- Chromosomes, Human, Pair 18/genetics
- Cytidine Deaminase
- Cytosine Deaminase/genetics
- DNA Nucleotidylexotransferase/genetics
- DNA, Neoplasm/genetics
- DNA-Binding Proteins/genetics
- Gene Expression
- Genes, RAG-1
- Humans
- Immunoglobulin Heavy Chains/genetics
- Immunoglobulin Variable Region/genetics
- Nuclear Proteins
- Precursor Cell Lymphoblastic Leukemia-Lymphoma/enzymology
- Precursor Cell Lymphoblastic Leukemia-Lymphoma/genetics
- Precursor Cell Lymphoblastic Leukemia-Lymphoma/immunology
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Neoplasm/genetics
- RNA, Neoplasm/metabolism
- Somatic Hypermutation, Immunoglobulin
- Translocation, Genetic
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Affiliation(s)
- Mardiah Suci Hardianti
- International Center for Medical Research (ICMR), Graduate School of Medicine, Kobe University, Kobe, Japan
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Viardot AA, Barth TFE, Möller P, Döhner H, Bentz M. Cytogenetic evolution of follicular lymphoma. Semin Cancer Biol 2003; 13:183-90. [PMID: 12959349 DOI: 10.1016/s1044-579x(03)00014-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Follicular lymphoma (FL) is closely associated with the chromosomal translocation t(14;18)(q32;q21), which results in an overexpression of the anti-apoptotic bcl-2 gene product leading to a survival advantage of B-lymphocytes. However, in animal models, this genomic aberration is not sufficient for the initiation of the malignant phenotype. Additional genomic rearrangements are required for disease progression. In this review, the most important additional aberrations and possible candidate genes in the respective genomic regions are discussed. In addition, relevant data regarding their role in disease progression as well as the association with clinical presentation and clinical course are presented.
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Wiemels JL, Leonard BC, Wang Y, Segal MR, Hunger SP, Smith MT, Crouse V, Ma X, Buffler PA, Pine SR. Site-specific translocation and evidence of postnatal origin of the t(1;19) E2A-PBX1 fusion in childhood acute lymphoblastic leukemia. Proc Natl Acad Sci U S A 2002; 99:15101-6. [PMID: 12415113 PMCID: PMC137550 DOI: 10.1073/pnas.222481199] [Citation(s) in RCA: 79] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2002] [Indexed: 11/18/2022] Open
Abstract
The t(1;19) translocation yields a fusion between E2A and PBX1 genes and occurs in 5% of acute lymphoblastic leukemia in children and adults. We used chromosomal translocations and Ig heavy chain (IGH)/T cell antigen receptor (TCR) rearrangements to develop an understanding of the etiology and natural history of this subtype of leukemia. We sequenced the genomic fusion between E2A and PBX1 in 22 preB acute lymphoblastic leukemias and two cell lines. The prenatal origin of the leukemia was assessed in 15 pediatric patients by screening for the clonotypic E2A-PBX1 translocation in neonatal blood spots, or Guthrie cards, obtained from the children at the time of birth. Two patients were determined to be weakly positive for the fusion at the time of birth, in contrast to previously studied childhood leukemia fusions, t(12;21), t(8;21), and t(4;11), which were predominantly prenatal. The presence of extensive N-nucleotides at the point of fusion in the E2A-PBX1 translocation as well as specific characteristics of the IGH/TCR rearrangements provided additional evidence for a postnatal, preB cell origin. Intriguingly, 16 of 24 breakpoints on the 3.2-kb E2A intron 14 were located within 5 bp, providing evidence for a site-specific recombination mechanism. Breakpoints on the 232-kb PBX1 intron 1 were more dispersed but highly clustered proximal to exon 2. In sum, the translocation breakpoints displayed evidence of unique temporal, ontological, and mechanistic formation than the previously analyzed pediatric leukemia translocation breakpoints and emphasize the need to differentiate cytogenetic and molecular subgroups for studies of leukemia causality.
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Affiliation(s)
- Joseph L Wiemels
- Department of Epidemiology and Biostatistics, University of California, San Francisco 94143, USA.
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