Board of Directors

Executive Leadership
Board of Directors
Medical Directors

Board of Directors

Taejoon Ahn, MD MPH CPE
President/Chief Executive Officer
Board Chairman

Taejoon Ahn, M.D. became the president of John Muir Medical Group (JMMG) in January of 2014. He oversees a medical group of over 300 clinicians, mostly in primary care. JMMG is the exclusive contracted provider of primary care services for John Muir Health, partnering closely for over 20 years. Prior to the presidency, Dr. Ahn served as vice president and medical director of urgent care services for JMMG. He also worked as faculty for the University of California, San Francisco's National HIV/AIDS Clinicians' Consultation Center. He is currently an Assistant Clinical Professor of Family & Community Medicine for UCSF.

Dr. Ahn also serves as director on the board of John Muir Health as well as the board of Canopy Health. Canopy Health is a joint venture between multiple provider groups to offer a large network in the San Francisco Bay Region.

Dr. Ahn received his medical degree from the University of California San Francisco, where he also completed a residency in Family & Community Medicine. He received his Masters in Public Health with an emphasis in Epidemiology from UC Berkeley. He is an alumnus of the California Healthcare Foundation's Leadership Fellowship and is a certified physician executive with the American Association for Physician Leadership (formerly the American College of Physician Executives).

Allen Obrinsky, MD
Pediatrician
Board Vice Chairman

Read Dr. Obrinsky's bio

Dr. Obrinsky has been practicing Pediatrics in the Tri-Valley community since 1989. He attended the School of Public Health at the University of California, Berkeley and obtained a M.S. in Epidemiology in 1982. He then attended medical school at Hahnemann University in Philadelphia and did his residency at Children’s Hospital Oakland. He is board certified by both the American Board of Pediatrics and the National Board of Physicians and Surgeons. Upon completing his residency in 1989 he joined San Ramon Valley Primary Care. Dr. Obrinsky joined the John Muir Medical Group in 2016 when SRVPC was acquired by John Muir Health. In 2018, Dr. Obrinsky was elected to the Board of Directors for John Muir Medical Group.

Dr. Obrinsky is married and with his wife Kristen has raised 3 sons. He enjoys playing golf, cooking, traveling, and spending time with family and friends.

Michael Schierman, MD
Medical Director Recruitment
Board Secretary

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Dr. Michael Schierman has been working in the San Ramon/Danville area for over 25 years. He and his wife, Suedale, moved to California in 1992 from Calgary, Alberta after completing his Family Medicine Residency at Foothills Hospital, University of Calgary. Dr. Schierman attended the University of Calgary to complete both his undergraduate degree in Psychology and Medical degree, then completed an Internship year at McGill University in Montreal, Quebec.

Dr. Schierman was initially recruited to practice Family Medicine by the San Ramon Medical Center in 1992. He has served in several leadership roles with this institution including Vice Chief of Staff, Secretary Treasurer and Head of Family Medicine. Early in his career, as a member of Hill Physicians, he participated in committee work. As time passed, he became an exclusive member of the Muir Medical Group IPA and served on their Executive Committee as the Vice President and briefly as interim President. Throughout his career with the IPA, he served on a number of IPA and John Muir Health Network committees and represented the IPA on the Network Board.

Dr. Schierman joined John Muir Medical Group in 2012 and is currently the Medical Director for Recruitment and serves on the Compensation committee. Dr. Schierman is also in full-time Family Practice in Danville, CA working with Dr. Christine Chang and Dr. Priya Swamy.

Outside of medicine, he enjoys being a loving husband to Suedale, his wife of 32 years, and also being a great dad to kids, Matt, 20 and Michaela, 18. Musically inclined, Dr. Schierman, plays guitar and enjoys helping Suedale with their church music program. He enjoys getting together with friends, working out and travelling. You may see Dr. Schierman in the Danville July 4^th parade as a "semi-professional" Elvis impersonator.

Karen Sonnenthal, NP
Director NP/PA and NP/PA Student Coordinator

Read Karen Sonnenthal's bio

Karen L. Sonnenthal has been with John Muir Medical Group since 1997, joining the group after graduating with a Masters in Nursing Science from Oregon Health Sciences University.

Born in California, Karen grew up in Baltimore Maryland, then moved to Oregon where she attended the University of Oregon and received an undergraduate degree in Biology and Psychology.

Karen is currently working as a Family Nurse Practitioner, and is the Associate Medical Director for the NP/PA group within John Muir Medical Group. She is also a member of the Quality and Compensation Committees.

Outside of work she enjoys hiking, gardening and reading as well as spending time with her boys—husband Eric, son Nate, and 2 fur pups Luca and Max.

Johnson Adeyanju, MD
Chair - Audit & Compliance Committee

Read Dr. Adeyanju's bio

Dr. Johnson Adeyanju graduated with honors in Bachelor of Science from the University of New Orleans, received Doctor of Medicine degree from Louisiana State University School of Medicine in New Orleans, Internship at the Los Angeles Community Hospital-USC School of Medicine, and completed Residency training in Internal Medicine at the University of California Davis VA Medical Center.

Dr. Adeyanju is board certified in Internal Medicine and A Fellow of the American College of Physicians.

Dr. Adeyanju served as the former Treasurer, President-Elect and The President of the Association of Nigerian Physicians in the Americas (ANPA). He’s a current member of ANPA Board of Directors and Executive council and is the Author of Deadly Revenge (Shadow of the Enemy), a mystery novel about Lagos, Nigeria.

Dr. Adeyanju is a founding member of John Muir Medical Group. He has served on JMMG quality committee, currently on the Governance committee and is the Physician Site Lead for JMMG Concord Urgent Care. He currently presides as the Co-Chair of Continuing Medical Education for physicians for John Muir Health.

Ethan Hollander, MD

Read Dr. Hollander's bio

Dr. Hollander joined John Muir Medical Group in 2003, practicing in a busy urgent care/family practice outpatient office serving both adults and children. He enjoys providing a range of services from continuity care of chronic diseases to urgent issues such a upper respiratory infections, orthopedic injuries, lacerations, outpatient gynecology, pediatric issues, and many other acute illnesses. Dr. Hollander is currently on the Board of Directors for the Group and chairs the Quality Committee.

Dr. Hollander earned an undergraduate degree in both Philosophy and General Biology from the University of California at San Diego, graduating Cum Laude. He attend Medical School at the University of California at Davis. While in school, he volunteered at a community clinic servicing uninsured patients in Sacramento. In addition, he was a member of the ethics committee and participated in Habitat for Humanity building projects. He completed his residency at Harbor Family Practice – University of California at Los Angeles. Dr. Hollander is board certified in Family Practice.

Dr. Hollander interests include literature, music, biking, camping and good food. He has lived in both England and New Zealand, each for one year, and has traveled numerous occasions to Thailand, Europe, Costa Rica and Mexico.

Rami G. Fasheh, MD
Medical Director of Inpatient Quality

Read Dr. Fasheh's bio

Rami G. Fasheh MD, has been with John Muir Medical Group since 2013. He is a board-certified Family Medicine physician and the Medical Director of Inpatient Quality at John Muir Health where he has served patients and families for the past eight years, receiving the Top Hospitalist award in 2015.

In his practice, Dr. Fasheh is committed to improving the health of his patients and their communities with quality and compassion. He also teaches medical residents at the UCSF/Family Medicine Residency Program at John Muir Health.

Dr. Fasheh holds a Bachelors’ Degree in Chemistry, minoring in Biology and Mathematics from the University of Louisville and a Medical Degree from the School of Medicine at the University of Dublin, Trinity College. He completed his Family Medicine Residency at Deaconess Hospital in Evansville, Indiana and a Hospital Medicine fellowship at St. Mary’s Medical Center. Dr. Fasheh is also an alum of the Alameda County’s Physician Leadership Program.

In his free time, Dr. Fasheh enjoys hiking, traveling, exercise and spending time with family and friends.

Robin Meezan, MD
Medical Director Pediatrics and Medical Student Coordinator

Read Meezan's bio

Robin Meezan was born and raised in Napa Valley. She went to college at Stanford University where she received a BA in Human Biology. Dr Meezan attended the University of Alabama School of Medicine for her MD and completed her pediatric residency at UCSF Benioff Children's Hospital Oakland. In 2006 she started as a pediatrician in Berkeley, and in 2013 she became a partner with John Muir Medical Group moving her practice to Orinda. Robin Meezan lives with her husband and two children in Orinda, she enjoys making pottery, cooking projects, tending to her fruit trees, and hiking all around the Bay Area.

Dr Meezan enjoys building relationships with parents caring for infants all the way through the teenage years. She has a special interest in helping with sleep and nutrition at all ages. She is the Medical Director for Pediatrics and the Medical Student Liaison for John Muir Medical Group.

Tanya Threewitt, MD
Executive Medical Director of Operations

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Dr. Tanya Threewitt has been working in Concord with John Muir Medical Group since 2002, splitting her time between her practice and administrative responsibilities to the group. She currently is the Executive Medical Director of Operations and the daily operations of the clinics in JMMG. Dr. Threewitt has also been heavily involved in Epic, John Muir Medical Groups' Electronic Health Record (EHR). In her spare time, she likes to read and travel.

Born and raised in San Jose, California, Dr. Threewitt received an undergraduate degree in psychology from UC Davis. She graduated from Hahnemann Medical School in Philadelphia and completed her Family Medicine residency through UC Davis in Modesto, California at the Stanislaus County Doctor’s Medical Center.

Neeta Milasincic, MD
Medical Director Inpatient Services

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Neeta Milasincic MD, FACP, has been with John Muir Medical Group since 2017. She is board-certified in Internal Medicine and is currently the Medical Director of Inpatient Services at John Muir Health. Dr. Milasincic is practiced Internist with more than 20 years of experience caring for patients as a Hospitalist and Ambulist.

Dr. Milasincic holds a Bachelor of Science Degree in Electrical Engineering from Baylor University, Waco, Texas, and a Medical Degree from Baylor College of Medicine in Houston, TX. She completed her residency at Christiana Care Health System in Newark Delaware where she was Chief Medical Resident in her fourth year and went on to act as the Department of Medicine, Consulting Internist and Resident Preceptor for many years.

In addition to teaching, Dr. Milasincic has been an invited lecturer covering topics including infertility, PCOS, endocrinology and nephrology. Her professional affiliations include American College of Physicians (Fellow) and Society of General Internal Medicine.

Kishore Nath, MD
Associate Program Director
Family Medicine Residency Program

Read Dr. Nath's bio

Kishore Nath, MD has been with John Muir Medical Group since October 2009 practicing Family Medicine. As the Medical Director of John Muir Health’s free mobile health clinic since 2010, Dr. Nath has actively pursued his passion for providing care to the vulnerable and underserved. In 2016 he joined the John Muir Health Family Medicine Residency Program, as their first Core Faculty member. Helping develop and implement the John Muir Health Residency program has been a fruitful experience combining his love of teaching and research with high quality patient care.

Dr. Nath is an assistant professor of Family and Community Medicine with UCSF. He is also a Clinical Adjunct Professor of Family Medicine at USC’s Keck School of Medicine, and Adjunct Assistant Professor with Touro University.

Dr. Nath received his undergraduate education at the University of California, Berkeley then returned home to attend medical school at the University of Southern California, Keck School of Medicine and completed his Internship and Residency at Long Beach Memorial Medical Center. He served as Chief Resident from 2000-2001 and received the resident teacher award in 2001 upon graduation from the Society of Teachers in Family Medicine. He is a graduate of the University of California, San Francisco Faculty Development Fellowship as well. Dr. Nath is board certified in Family Medicine.

Born and raised in Southern California, he remains a devoted Dodgers and Lakers fan. He enjoys watching his kids grow and tries to return to the beach whenever he can. Dr. Nath is currently working on a project to bring supplies and evidence based training to a medical clinic on the outskirts of Arequipa, Perú. Service to patients at home and abroad is invigorating for Dr. Nath and teaching the next generation of physicians to serve with humility and enthusiasm is his small contribution to the John Muir Health community.

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