Brian A Walker (Brian Walker, B A Walker)

Scopus Author ID Loop profile ORCID

Publication Activity (10 Years)

Years Active: 2015-2023
Publications (10 Years): 41

Top Venues

Leukemia

Blood cancer journal

Nature communications

Blood

Myeloma Institute

This page only lists publications with an associated author ORCID identifier.

Affiliation History

Myeloma Institute Nov 1o 2015 - Oct 31o 2019

United States

Director of Research

Publications

Enze Liu, Nathan Becker, Parvathi Sudha, Chuanpeng Dong, Yunlong Liu, Jonathan J Keats, Gareth Morgan, Brian A Walker
Alternative splicing in multiple myeloma is associated with the non-homologous end joining pathway. Blood cancer journal 13 (1) (2023)
Brian A Walker, Travis S Johnson, Parvathi Sudha, Enze Liu, Patrick Blaney, Gareth J Morgan, Vivek Chopra, Cedric Dos Santos, Michael Nixon, Kun Huang, Attaya Suvannasankha, Mohammad Abu Zaid, Rafat Abonour
Identifying 1q amplification and PHF19 expressing high-risk cells associated with relapsed/refractory multiple myeloma. Research square (2023)
Enze Liu, Parvathi Sudha, Nathan Becker, Oumaima Jaouadi, Attaya Suvannasankha, Kelvin Lee, Rafat Abonour, Mohammad Abu Zaid, Brian A Walker
Identifying novel mechanisms of biallelic TP53 loss refines poor outcome for patients with multiple myeloma. Blood cancer journal 13 (1) (2023)
Enze Liu, Nathan Becker, Parvathi Sudha, Chuanpeng Dong, Yunlong Liu, Jonathan J Keats, Gareth Morgan, Brian A Walker
Alternative splicing in multiple myeloma is associated with the non-homologous end joining pathway. Blood cancer journal 13 (1) (2023)
Eileen Mary Boyle, Patrick Blaney, James H Stoeckle, Yubao Wang, Hussein Ghamlouch, Dylan Gagler, Marc J Braunstein, Louis Williams, Avital Tenenbaum, Ariel M Siegel, Xiaoyi Chen, Gaurav Varma, Jason Avigan, Alexander Li, Monica Jinsi, David Kaminetzky, Arnaldo Arbini, Lydia Montes, Jill Corre, Even Holth Rustad, Carl Ola Landgren, Francesco Maura, Brian A Walker, Michael A Bauer, Benedetto Bruno, Aristotelis Tsirigos, Faith E Davies, Gareth J Morgan
Multiomic mapping of acquired chromosome 1 copy number and structural variants to identify therapeutic vulnerabilities in multiple myeloma. Clinical cancer research : an official journal of the American Association for Cancer Research (2023)
Enze Liu, Nathan Becker, Parvathi Sudha, Chuanpeng Dong, Yunlong Liu, Jonathan J Keats, Gareth Morgan, Brian A Walker
Alternative splicing in multiple myeloma is associated with the non-homologous end joining pathway. Blood cancer journal 13 (1) (2023)
Parvathi Sudha, Aarif Ahsan, Cody Ashby, Tasneem Kausar, Akhil Khera, Mohammad H Kazeroun, Chih-Chao Hsu, Lin Wang, Evelyn Fitzsimons, Outi Salminen, Patrick Blaney, Magdalena Czader, Jonathan Williams, Mohammad Abu Zaid, Naser Ansari-Pour, Kwee L Yong, Frits van Rhee, William E Pierceall, Gareth J Morgan, Erin Flynt, Sarah Gooding, Rafat Abonour, Karthik Ramasamy, Anjan Thakurta, Brian A Walker
Myeloma Genome Project Panel is a Comprehensive Targeted Genomics Panel for Molecular Profiling of Patients with Multiple Myeloma. Clinical cancer research : an official journal of the American Association for Cancer Research 28 (13) (2022)
Daniel Rico, Daniel Kent, Nefeli Karataraki, Aneta Mikulasova, Rolando Berlinguer Palmini, Brian A Walker, Biola M Javierre, Lisa J Russell, Chris A Brackley
High-resolution simulations of chromatin folding at genomic rearrangements in malignant B cells provide mechanistic insights into proto-oncogene deregulation. Genome research (2022)
Naser Ansari-Pour, Mehmet K Samur, Erin Flynt, Sarah Gooding, Fadi Towfic, Nicholas Stong, Maria Ortiz Estevez, Konstantinos Mavrommatis, Brian A Walker, Gareth J Morgan, Nikhil C Munshi, Herve Avet Loiseau, Anjan Thakurta
Whole-genome analysis identifies novel drivers and high-risk double-hit events in relapsed/refractory myeloma. Blood (2022)
Faith E Davies, Charlotte Pawlyn, Saad Z Usmani, Jesús San F Miguel, Hermann Einsele, Eileen Mary Boyle, Jill Corre, Daniel Auclair, Hearn Jay Cho, Sagar Lonial, Pieter Sonneveld, A Keith Stewart, Peter Leif Bergsagel, Martin F Kaiser, Katja Weisel, Jonathan J Keats, Joseph R Mikhael, Kathryn E Morgan, Irene M Ghobrial, Robert Z Orlowski, Carl Ola Landgren, Francesca Gay, Joseph Caers, Wee-Joo Chng, Ajai Chari, Brian A Walker, Shaji K Kumar, Luciano José Megale Costa, Kenneth C Anderson, Gareth J Morgan
Perspectives on the Risk-Stratified Treatment of Multiple Myeloma. Blood cancer discovery 3 (4) (2022)
Mark Bustoros, Shankara Anand, Romanos Sklavenitis-Pistofidis, Robert A Redd, Eileen Mary Boyle, Benny Zhitomirsky, Andrew J Dunford, Yu-Tzu Tai, Selina J Chavda, Cody Boehner, Carl Jannes Neuse, Mahshid Rahmat, Andrew T Hutchinson, Tineke Casneuf, Raluca Verona, Efstathis Kastritis, Lorenzo Trippa, Chip Stewart, Brian A Walker, Faith E Davies, Meletios- Athanasios Dimopoulos, Peter Leif Bergsagel, Kwee L Yong, Gareth J Morgan, François Aguet, Gad A Getz, Irene M Ghobrial
Genetic subtypes of smoldering multiple myeloma are associated with distinct pathogenic phenotypes and clinical outcomes. Nature communications 13 (1) (2022)
Cody Ashby, Eileen Mary Boyle, Michael A Bauer, Aneta Mikulasova, Christopher Paul Wardell, Louis Williams, Ariel Siegel, Patrick Blaney, Marc Braunstein, David Kaminetsky, Jonathan J Keats, Francesco Maura, Carl Ola Landgren, Brian A Walker, Faith E Davies, Gareth J Morgan
Structural variants shape the genomic landscape and clinical outcome of multiple myeloma. Blood cancer journal 12 (5) (2022)
Leo Rasche, Carolina D Schinke, Francesco Maura, Michael A Bauer, Cody Ashby, Shayu Deshpande, Alexandra M Poos, Maurizio Zangari, Sharmilan Thanendrarajan, Faith E Davies, Brian A Walker, Bart Barlogie, Carl Ola Landgren, Gareth J Morgan, Frits van Rhee, Niels Weinhold
The spatio-temporal evolution of multiple myeloma from baseline to relapse-refractory states. Nature communications 13 (1) (2022)
Chuanpeng Dong, Annamaria Cesarano, Giuseppe Bombaci, Jill L Reiter, Christina Y Yu, Yue Wang, Zhaoyang Jiang, Mohammad Abu Zaid, Kun Huang, Xiongbin Lu, Brian A Walker, Fabiana Perna, Yunlong Liu
Intron retention-induced neoantigen load correlates with unfavorable prognosis in multiple myeloma. Oncogene 40 (42) (2021)
Bénedith Oben, Guy Froyen, Kylee H Maclachlan, Daniel A Leongamornlert, Federico Abascal, Binbin Zheng-Lin, Venkata Yellapantula, Andriy Derkach, Ellen Geerdens, Benjamin T Diamond, Ingrid Arijs, Brigitte Maes, Kimberly Vanhees, Malin L Hultcrantz, Elisabet E Manasanch, Dickran Kazandjian, Alexander Lesokhin, Ahmet Dogan, Yanming Zhang, Aneta Mikulasova, Brian A Walker, Gareth J Morgan, Peter J Campbell, Carl Ola Landgren, Jean-Luc Rummens, Niccolò Bolli, Francesco Maura
Whole-genome sequencing reveals progressive versus stable myeloma precursor conditions as two distinct entities. Nature communications 12 (1) (2021)
Eileen M Boyle, Louis Williams, Patrick Blaney, Cody Ashby, Michael A Bauer, Brian A Walker, Hussein Ghamlouch, Jinyoung Choi, Emeline Perrial, Yubao Wang, Jessica Caro, James H Stoeckle, Arnaldo Arbini, David Kaminetzky, Marc Braunstein, Benedetto Bruno, Beatrice Razzo, Benjamin T Diamond, Kylee H Maclachlan, Francesco Maura, Carl Ola Landgren, Rachel Litke, Christopher D Fegan, Jonathan J Keats, Daniel Auclair, Faith E Davies, Gareth J Morgan
Improving prognostic assignment in older adults with multiple myeloma using acquired genetic features, clonal hemopoiesis and telomere length. Leukemia (2021)
J R Jones, A Barber, Yann-Vaï Le Bihan, N Weinhold, Cody Ashby, Brian A Walker, Christopher Paul Wardell, H Wang, M F Kaiser, G H Jackson, F E Davies, R Chopra, Gareth J Morgan, Charlotte Pawlyn
Mutations in CRBN and other cereblon pathway genes are infrequently associated with acquired resistance to immunomodulatory drugs. Leukemia 35 (10) (2021)
Eileen M Boyle, Adam Rosenthal, Hussein Ghamlouch, Yan Wang, Phillip Farmer, Michael W Rutherford, Cody Ashby, Michael A Bauer, Sarah K Johnson, Christopher Paul Wardell, Yubao Wang, Antje Hoering, Carolina D Schinke, Sharmilan Thanendrarajan, Maurizio Zangari, Bart Barlogie, Madhav V Dhodapkar, Faith E Davies, Gareth J Morgan, Frits van Rhee, Brian A Walker
Plasma cells expression from smouldering myeloma to myeloma reveals the importance of the PRC2 complex, cell cycle progression, and the divergent evolutionary pathways within the different molecular subgroups. Leukemia (2021)
Aneta Mikulasova, Daniel Kent, Marco Trevisan-Herraz, Nefeli Karataraki, Kent T M Fung, Cody Ashby, Agata Cieslak, Shmuel Yaccoby, Frits van Rhee, Maurizio Zangari, Sharmilan Thanendrarajan, Carolina Schinke, Gareth J Morgan, Vahid Asnafi, Salvatore Spicuglia, Chris A Brackley, Anne E Corcoran, Sophie Hambleton, Brian A Walker, Daniel Rico, Lisa J Russell
Epigenomic translocation of H3K4me3 broad domains over oncogenes following hijacking of super-enhancers. Genome research 32 (7) (2021)
Eileen M Boyle, Shayu Deshpande, Ruslana Tytarenko, Cody Ashby, Yan Wang, Michael A Bauer, Sarah K Johnson, Christopher Paul Wardell, Sharmilan Thanendrarajan, Maurizio Zangari, Thierry Facon, Charles Dumontet, Bart Barlogie, Arnaldo Arbini, Even H Rustad, Francesco Maura, Carl Ola Landgren, Fenghuang Zhan, Frits van Rhee, Carolina D Schinke, Faith E Davies, Gareth J Morgan, Brian A Walker
The molecular make up of smoldering myeloma highlights the evolutionary pathways leading to multiple myeloma. Nature communications 12 (1) (2021)
Samrat Roy Choudhury, Cody Ashby, Ruslana Tytarenko, Michael Bauer, Yan Wang, Shayu Deshpande, Judith Den, Carolina Schinke, Maurizio Zangari, Sharmilan Thanendrarajan, Faith E Davies, Frits van Rhee, Gareth J Morgan, Brian A Walker
The functional epigenetic landscape of aberrant gene expression in molecular subgroups of newly diagnosed multiple myeloma. Journal of hematology & oncology 13 (1) (2020)
Brian A Walker
The Chromosome 13 Conundrum in Multiple Myeloma. Blood cancer discovery 1 (1) (2020)
Shayu Deshpande, Ruslana G Tytarenko, Yan Wang, Eileen M Boyle, Cody Ashby, Carolina D Schinke, Sharmilan Thanendrarajan, Maurizio Zangari, Fenghuang Zhan, Faith E Davies, Gareth J Morgan, Frits van Rhee, Brian A Walker
Monitoring treatment response and disease progression in myeloma with circulating cell-free DNA. European journal of haematology 106 (2) (2020)
Eileen Mary Boyle, Cody Ashby, Ruslana G Tytarenko, Shayu Deshpande, Hongwei Wang, Yan Wang, Adam Rosenthal, Jeffrey Sawyer, Erming Tian, Erin Flynt, Antje Hoering, Sarah K Johnson, Michael W Rutherford, Christopher P Wardell, Michael A Bauer, Charles Dumontet, Thierry Facon, Sharmilan Thanendrarajan, Carolina D Schinke, Maurizio Zangari, Frits van Rhee, Bart Barlogie, David Cairns, Graham Jackson, Anjan Thakurta, Faith E Davies, Gareth J Morgan, Brian A Walker
BRAF and DIS3 Mutations Associate with Adverse Outcome in a Long-term Follow-up of Patients with Multiple Myeloma. Clinical cancer research : an official journal of the American Association for Cancer Research 26 (10) (2020)
Michael Mason, Carolina Schinke, Christine L P Eng, Fadi Towfic, Fred Gruber, Andrew P Dervan, Brian S White, Aditya Pratapa, Yuanfang Guan, Hongjie Chen, Yi Cui, Bailiang Li, Thomas Yu, Elias Chaibub Neto, Konstantinos Mavrommatis, Maria Ortiz, Valeriy Lyzogubov, Kamlesh Bisht, Hongyue Y Dai, Frank Schmitz, Erin Flynt, null Dan Rozelle, Samuel A Danziger, Alexander Ratushny, null null, William S Dalton, Hartmut Goldschmidt, Herve Avet-Loiseau, Mehmet Samur, Boris Hayete, Pieter Sonneveld, Kenneth H Shain, Nikhil Munshi, Daniel Auclair, Dirk Hose, Gareth Morgan, Matthew Trotter, Douglas Bassett, Jonathan Goke, Brian A Walker, Anjan Thakurta, Justin Guinney
Multiple Myeloma DREAM Challenge reveals epigenetic regulator PHF19 as marker of aggressive disease. Leukemia 34 (7) (2020)
Samuel A Danziger, Mark McConnell, Jake Gockley, Mary H Young, Adam Rosenthal, Frank Schmitz, David J Reiss, Phillip Farmer, Daisy V Alapat, Amrit P Singh, Cody Ashby, Michael A Bauer, Yan Ren, Kelsie Smith, Suzana S Couto, Frits van Rhee, Faith Davies, Maurizio Zangari, Nathan Petty, Robert Z Orlowski, Madhav V Dhodapkar, Wilbert B Copeland, Brian Fox, Antje Hoering, Alison Fitch, Katie Newhall, Bart Barlogie, Matthew W B Trotter, Robert M Hershberg, Brian A Walker, Andrew P Dervan, Alexander V Ratushny, Gareth J Morgan
Bone marrow microenvironments that contribute to patient outcomes in newly diagnosed multiple myeloma: A cohort study of patients in the Total Therapy clinical trials. PLoS medicine 17 (11) (2020)
Carolina D Schinke, Eileen M Boyle, Cody Ashby, Yan Wang, Valeriy Lyzogubov, Christopher Paul Wardell, Pingping Qu, Antje Hoering, Shayu Deshpande, Katie Ryan, Sharmilan Thanendrarajan, Meera Mohan, Naveen Yarlagadda, Maliha Khan, Samrat Roy Choudhury, Maurizio Zangari, Frits van Rhee, Faith Davies, Bart Barlogie, Gareth Morgan, Brian A Walker
Genomic analysis of primary plasma cell leukemia reveals complex structural alterations and high-risk mutational patterns. Blood cancer journal 10 (6) (2020)
Alex Pearson, Paula Proszek, Javier Pascual, Charlotte Fribbens, Monee K Shamsher, Belinda Kingston, Ben O'Leary, Maria T Herrera-Abreu, Rosalind J Cutts, Isaac Garcia-Murillas, Hannah Bye, Brian A Walker, David Gonzalez De Castro, Lina Yuan, Sabri Jamal, Michael Hubank, Elena Lopez-Knowles, Eugene F Schuster, Mitch Dowsett, Peter Osin, Ashutosh Nerurkar, Marina Parton, Alicia F C Okines, Stephen R D Johnston, Alistair Ring, Nicholas C Turner
Inactivating NF1 Mutations Are Enriched in Advanced Breast Cancer and Contribute to Endocrine Therapy Resistance. Clinical cancer research : an official journal of the American Association for Cancer Research 26 (3) (2019)
Jeffrey R Sawyer, Erming Tian, Brian A Walker, Christopher Wardell, Janet L Lukacs, Gael Sammartino, Clyde Bailey, Carolina D Schinke, Sharmilan Thanendrarajan, Faith E Davies, Gareth J Morgan, Bart Barlogie, Maurizio Zangari, Frits van Rhee
An acquired high-risk chromosome instability phenotype in multiple myeloma: Jumping 1q Syndrome. Blood cancer journal 9 (8) (2019)
Brian A Walker
Knick-knack PADIMAC. Blood 132 (20) (2019)
Julie Støve Bødker, Rasmus Froberg Brøndum, Alexander Schmitz, Anna Amanda Schönherz, Ditte Starberg Jespersen, Mads Sønderkær, Charles Vesteghem, Hanne Due, Caroline Holm Nørgaard, Martin Perez-Andres, Mehmet Kemal Samur, Faith Davies, Brian A Walker, Charlotte Pawlyn, Martin Kaiser, David Johnson, Uta Bertsch, Annemiek Broyl, Mark van Duin, Rajen Shah, Preben Johansen, Martin Agge Nørgaard, Richard J Samworth, Pieter Sonneveld, Hartmut Goldschmidt, Gareth J Morgan, Alberto Orfao, Nikhil Munshi, Hans Erik Johnson, Tarec El-Galaly, Karen Dybkær, Martin Bøgsted
A multiple myeloma classification system that associates normal B-cell subset phenotypes with prognosis. Blood advances 2 (18) (2019)
L Rasche, D Alapat, M Kumar, G Gershner, J McDonald, C P Wardell, R Samant, R Van Hemert, J Epstein, A F Williams, S Thanendrarajan, C Schinke, Michael A Bauer, Cody Ashby, R G Tytarenko, F van Rhee, Brian A Walker, M Zangari, B Barlogie, F E Davies, G J Morgan, N Weinhold
Combination of flow cytometry and functional imaging for monitoring of residual disease in myeloma. Leukemia 33 (7) (2018)
Gareth J Morgan, Jie He, Ruslana Tytarenko, Purvi Patel, Owen W Stephens, Shan Zhong, Shayu Deshpande, Michael A Bauer, Niels Weinhold, Carolina Schinke, Leo Rasche, Mark Bailey, Siraj Ali, Jeff Ross, Vincent A Miller, Phillip Stephens, Sharmilan Thanendrarajan, Maurizio Zangari, Frits van Rhee, Tariq Mughal, Faith E Davies, Brian A Walker
Kinase domain activation through gene rearrangement in multiple myeloma. Leukemia 32 (11) (2018)
Eileen Mary Boyle, Cody Ashby, Christopher Paul Wardell, Dorota Rowczenio, Sajitha Sachchithanantham, Yan Wang, Sarah K Johnson, Michael A Bauer, Niels Weinhold, Martin F Kaiser, David C Johnson, John R Jones, Charlotte Pawlyn, Paula Proszek, Carolina Schinke, Thierry Facon, Charles Dumontet, Faith E Davies, Gareth J Morgan, Brian A Walker, Ashutosh D Wechalekar
The genomic landscape of plasma cells in systemic light chain amyloidosis. Blood 132 (26) (2018)
Brian A Walker, Konstantinos Mavrommatis, Christopher P Wardell, T Cody Ashby, Michael A Bauer, Faith Davies, Adam Rosenthal, Hongwei Wang, Pingping Qu, Antje Hoering, Mehmet Samur, Fadi Towfic, Maria Ortiz, Erin Flynt, Zhinuan Yu, Zhihong Yang, Dan Rozelle, John Obenauer, Matthew Trotter, Daniel Auclair, Jonathan J Keats, Niccolo Bolli, Mariateresa Fulciniti, Raphael Szalat, Phillipe Moreau, Brian Durie, A Keith Stewart, Hartmut Goldschmidt, Marc S Raab, Hermann Einsele, Pieter Sonneveld, Jesus San Miguel, Sagar Lonial, Graham H Jackson, Kenneth C Anderson, Herve Avet-Loiseau, Nikhil Munshi, Anjan Thakurta, Gareth Morgan
A high-risk, Double-Hit, group of newly diagnosed myeloma identified by genomic analysis. Leukemia 33 (1) (2018)
Charlotte Pawlyn, Andrea Loehr, Cody Ashby, Ruslana Tytarenko, Shayu Deshpande, James Sun, Kyle Fedorchak, Tariq Mughal, Faith E Davies, Brian A Walker, Gareth J Morgan
Loss of heterozygosity as a marker of homologous repair deficiency in multiple myeloma: a role for PARP inhibition? Leukemia 32 (7) (2018)
Brian A Walker, Konstantinos Mavrommatis, Christopher Paul Wardell, T Cody Ashby, Michael Bauer, Faith E Davies, Adam Rosenthal, Hongwei Wang, Pingping Qu, Antje Hoering, Mehmet Samur, Fadi Towfic, Maria Ortiz, Erin Flynt, Zhinuan Yu, Zhihong Yang, Dan Rozelle, John Obenauer, Matthew Trotter, Daniel Auclair, Jonathan Keats, Niccolo Bolli, Mariateresa Fulciniti, Raphael Szalat, Philippe Moreau, Brian Durie, A Keith Stewart, Hartmut Goldschmidt, Marc S Raab, Hermann Einsele, Pieter Sonneveld, Jesus San Miguel, Sagar Lonial, Graham H Jackson, Kenneth C Anderson, Herve Avet-Loiseau, Nikhil Munshi, Anjan Thakurta, Gareth J Morgan
Identification of novel mutational drivers reveals oncogene dependencies in multiple myeloma. Blood 132 (6) (2018)
L Rasche, S S Chavan, O W Stephens, P H Patel, R Tytarenko, C Ashby, Michael A Bauer, C Stein, S Deshpande, C Wardell, T Buzder, G Molnar, M Zangari, F van Rhee, S Thanendrarajan, C Schinke, J Epstein, F E Davies, Brian A Walker, T Meissner, B Barlogie, G J Morgan, N Weinhold
Spatial genomic heterogeneity in multiple myeloma revealed by multi-region sequencing. Nature communications 8 (1) (2017)
David C Johnson, Oleg Lenive, Jonathan Mitchell, Graham Jackson, Roger Owen, Mark Drayson, Gordon Cook, John R Jones, Charlotte Pawlyn, Faith E Davies, Brian A Walker, Christopher Wardell, Walter M Gregory, David Cairns, Gareth J Morgan, Richard S Houlston, Martin F Kaiser
Neutral tumor evolution in myeloma is associated with poor prognosis. Blood 130 (14) (2017)
V Shah, A L Sherborne, Brian A Walker, David C Johnson, E M Boyle, S Ellis, D B Begum, P Z Proszek, J R Jones, Charlotte Pawlyn, S Savola, M W Jenner, M T Drayson, R G Owen, R S Houlston, David A Cairns, W M Gregory, G Cook, F E Davies, G H Jackson, G J Morgan, M F Kaiser
Prediction of outcome in newly diagnosed myeloma: a meta-analysis of the molecular profiles of 1905 trial patients. Leukemia 32 (1) (2017)
Brian A Walker, Christopher P Wardell, Alex Murison, Eileen M Boyle, Dil B Begum, Nasrin M Dahir, Paula Z Proszek, Lorenzo Melchor, Charlotte Pawlyn, Martin F Kaiser, David C Johnson, Ya-Wei Qiang, John R Jones, David A Cairns, Walter M Gregory, Roger G Owen, Gordon Cook, Mark T Drayson, Graham H Jackson, Faith E Davies, Gareth J Morgan
APOBEC family mutational signatures are associated with poor prognosis translocations in multiple myeloma. Nature communications 6 (2015)

Brian A Walker.css-eqlu8i{font-size:small;padding-left:4px;} (Brian Walker, B A Walker)

Publication Activity (10 Years)

Top Topics

Top Venues

Brian A Walker (Brian Walker, B A Walker)