Xandra Owens Breakefield is an American neurologist who is a professor of neurology at the Harvard Medical School. Her research makes use of molecular genetics to understand the origins of inherited neurological diseases.

As a child, Breakfield was undecided about what she would do when she grew up. Her mother told her she had to attend college or work in a dime store, so Breakefield decided to attend college.^[1] Breakefield enrolled as an undergraduate at Wilson College, where she discovered the joy of learning.^[2][1] She was an undergraduate at the time that DNA had first been described, which inspired her to pursue something scientific.^[1] She earned her doctorate at Georgetown University,^{[citation needed]} then was a postdoctoral researcher at the National Institutes of Health, where she worked alongside Marshall Warren Nirenberg.^[1] She then moved to the United States' first human genetics laboratory.^[1] She was inspired by human genetics, and eventually led the team that discovered the genetic markers for the dystonia gene.^[1][3]

Breakefield's early work considered the nerve growth factor, a protein involved in the development of sensory neurons, catechol-O-methyltransferase and monoamine oxidase.^[4]

Breakefield uses molecular genetics to understand inherited variations in neurological disease.^[5] To achieve this, she uses new viral vectors to enhance gene delivery and develops new therapeutic modalities.^[6] In particular, she has developed strategies to identify the genes that cause movement disorders (e.g. early-onset torsion dystonia and X-linked dystonia parkinsonism). In addition, she has studied the extracellular vesicles that are released by cells of brain tumor, looking at how they modify their microenvironment to promote tumor growth.^[7]

• Mathilde Solowey Neuroscience Award^[4]
• NARSAD Distinguished Investigator Award^[8]

• Brunner, H. G.; Nelen, M.; Breakefield, X. O.; Ropers, H. H.; van Oost, B. A. (1993-10-22). "Abnormal Behavior Associated with a Point Mutation in the Structural Gene for Monoamine Oxidase A". Science. 262 (5133): 578–580. Bibcode:1993Sci...262..578B. doi:10.1126/science.8211186. ISSN 0036-8075. PMID 8211186.
• Skog, Johan; Würdinger, Tom; van Rijn, Sjoerd; Meijer, Dimphna H.; Gainche, Laura; Curry, William T.; Carter, Bob S.; Krichevsky, Anna M.; Breakefield, Xandra O. (December 2008). "Glioblastoma microvesicles transport RNA and proteins that promote tumour growth and provide diagnostic biomarkers". Nature Cell Biology. 10 (12): 1470–1476. doi:10.1038/ncb1800. ISSN 1465-7392. PMC 3423894. PMID 19011622.
• EL Andaloussi, Samir; Mäger, Imre; Breakefield, Xandra O.; Wood, Matthew J. A. (2013-04-15). "Extracellular vesicles: biology and emerging therapeutic opportunities". Nature Reviews Drug Discovery. 12 (5): 347–357. doi:10.1038/nrd3978. ISSN 1474-1776. PMID 23584393. S2CID 205478102.

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