Advanced Longevity

Meet Our Team

Dr. Donald “Dean” Yarbro, Jr., MD

Dr. Dean Yarbro is a Board-Certified Radiologist with over 40 years of clinical experience in Diagnostic Radiology. A graduate of Texas Tech University Health Sciences Center School of Medicine, Dr. Yarbro has built a respected career marked by his commitment to precision, clarity, and collaboration in medical imaging. Throughout his extensive career, Dr. Yarbro has partnered with physicians across a wide range of specialties to deliver high-quality diagnostic insights that inform patient care and treatment decisions. At Advanced Longevity, he brings his deep expertise and trusted clinical judgment to support proactive, data-driven health strategies for long-term wellness.

Dr. Keith Lewis, MD

Dr. Keith Michael Lewis, MD, is a seasoned radiologist, with nearly four decades of expertise in both diagnostic and nuclear radiology. A Vanderbilt alumnus and UCLA-trained specialist, he is respected for his technical proficiency, thorough patient care, and professional conduct. His practice at Advanced Longevity is well-regarded, with top-tier quality and patient satisfaction.

Dr. Ramy Mankarious, MD

Dr. Ramy Mankarious is a board-certified anesthesiologist who earned his medical degree from UT McGovern Medical School and completed his residency at Harvard Medical School / Massachusetts General Hospital. He spent over two decades with Greater Houston Anesthesiology, where he helped expand the group into one of the nation’s largest through strategic leadership and operations management. In addition to his work in anesthesiology, Dr. Mankarious is passionate about longevity, wellness, and weight management. He is committed to helping patients thrive both in and out of the operating room through personalized, evidence-based care. He lives in Houston with his wife and three daughters.

Dr. Ryan Williamson, MD

Dr. Ryan Williamson is a board-certified neurologist, U.S. Navy veteran, and a leading voice in the field of brain health and human longevity. He brings a wealth of clinical expertise and a deep passion for optimizing cognitive function, extending healthspan, and empowering individuals to lead high-performing, purpose-driven lives.

At Advanced Longevity, Dr. Williamson focuses on brain and cognitive health, leveraging cutting-edge, evidence-based strategies to support mental clarity, neuroprotection, and long-term vitality. With a strong foundation in functional and holistic medicine, he also serves as a trusted resource for broader wellness approaches—making him an invaluable asset to both patients and the team. Driven by a mission to help people feel better, think sharper, and live longer, Dr. Williamson is committed to proactive, personalized care that delivers meaningful and lasting results.

Natalie Greer, MSN, AGNP-C

Natalie Greer is a board-certified nurse practitioner with over 15 years of experience in patient-centered medicine and a deep passion for proactive wellness, functional health and preventive care. She blends clinical expertise with a compassionate, individualized approach to help patients optimize their health at every stage of life. Natalie is dedicated to early detection, education, and empowering individuals to take an active role in their long-term well-being.

Ashley Williams, PhD (WIP), BSN, RN

Ashley is a registered nurse with a 20-year career marked by growth and specialization. Currently the Clinical Operations Leader for Advanced Longevity, she is also pursuing a doctorate in functional and integrative medicine to advance her vision of a healthcare system focused on prevention, holistic wellness, and patient empowerment.

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