U.S. Department of Health and Human Services

Digestive Diseases Branch Clinical Gastroenterology Fellows

Welcome to the Gastroenterology Fellowship Program at the National Institutes of Health!

The Digestive Diseases Branch at the National Institute of Diabetes, Digestive and Kidney Diseases has a long tradition of training fellows for a career in academic Gastroenterology and Hepatology. Under the leadership of Dr. Stephen Wank, Chief of the Digestive Diseases Branch, the program has a strong commitment to provide excellent training to its fellows to develop the skills necessary to become independent physician-scientists in the field of Gastroenterology and Hepatology.

The 3-year combined fellowship in Gastroenterology and Hepatology is a joint program with the University of Maryland Medical Center. The first year of the fellowship is purely clinical and is centered at the University of Maryland Medical Center and Baltimore VA Medical Center (BVAMC). The second and third years are spent at the NIH Clinical Center and predominantly focused on clinical and/or translational research.

Current Digestive Disease Branch Clinical Gastroenterology Fellows:​

Thomas Simcox, M.D.Thomas Simcox, M.D.

3rd year

Residency: University of Maryland Medical Center, Baltimore, MD
Medical Degree: Virginia Commonwealth University School of Medicine, Richmond, VA

One of my research projects involves studying the effects of an experimental gastrin receptor blocker in patients with gastric carcinoid tumors. In this study, we are evaluating the safety and efficacy of this investigational drug on gastric carcinoid tumors and gastric enterochromaffin-like cells in patients with Zollinger-Ellison Syndrome. Additionally, I am also involved in a study utilizing the wireless SmartPill© capsule as a novel tool in the measurement of gastric acid in patients with gastric acid hypersecretion. The goal of this study is to evaluate the applicability of the SmartPill© in the management of patients with gastroesophageal reflux disease.

Mark T. Voellinger, M.D.

Mark T. Voellinger, M.D.

3rd year

Residency: West Virginia Univerisity Hospital, Morgantown, WV
Medical Degree: West Virginia University School of Medicine, Morgantown, WV

My primary research focus is in the study of familial midgut gastrointestinal carcinoid tumors. Sporadic carcinoid tumors are a rare type of tumor arising from neuroendocrine cells. We study a familial form of these malignancies transmitted by autosomal dominant inheritance, affecting two or more members within a given family. Our goals are to evaluate the presentation and natural history of familial midgut carcinoid and determine the most optimal methods for diagnosing and following the disease over time through our use of sophisticated imaging and serum tests. Also under investigation is the search for and analysis of the genes responsible for these familial tumors. We believe the information acquired from our work will also assist in the diagnosis and management of other neuroendocrine tumors and familial malignancies.

Jim Chou, M.D.Jim Chou, M.D.

2rd year

Residency: Cedars-Sinai Medical Center / UCLA, Los Angeles, CA
Medical Degree: Boston University School of Medicine, Boston, MA

One of my gastrointestinal research projects focuses on study of Multiple Endocrine Neoplasia type-1, Zollinger-Ellison Syndrome and their genetic and phenotypic manifestations and correlations. Other areas of interest include roles of gut microbiome in gastrointestinal diseases and intestinal infections.

Nancy Ho, M.D.Nancy Ho, M.D.

2rd year

Residency: McGaw Medical Center of Northwestern University, Chicago, IL
Medical Degree: Feinberg School of Medicine, Northwestern University, Chicago, IL

I am currently involved in a study following the largest cohort of patients with chronic granulomatous disease, and I am helping to manage the gastrointestinal manifestations and complications of this rare disease. I am also involved in a phase 1 trial of sirolimus in the treatment of eosinophilic gastrointestinal disease. Finally, I am helping to characterize the gastrointestinal manifestations of a yet, unnamed familial mast cell degranulation disorder.

Recent graduates and current position:

Preet Bagi, M.D.Preet Bagi, M.D.

Inflammatory Bowel Disease Advanced Fellowship - University of California
San Diego Inflammatory Bowel Disease Center



Christopher Koh, M.D. M.H.Sc.Christopher Koh, M.D. M.H.Sc.

Staff Clinician, Liver Diseases Branch, National Institute of Diabetes and Digestive and Kidney Diseases
National Institutes of Health


Sajneet Khangura, M.D.Sajneet Khangura, M.D.

Assistant Professor – Clinical Department of Medicine
Division of Digestive Diseases, The University of Mississippi Medical Center, Jackson, MS



Apurva Trivedi, M.D.Apurva Trivedi, M.D.

Assistant Professor – Texas A&M Health Science Center College of Medicine
Department of Gastroenterology, Scott & White Healthcare, Killeen, TX



Manish Arora, M.B.B.S.Manish Arora, M.B.B.S.

Practicing Gastroenterologist, Decatur, AL




Douglas Weinstein, M.D.Douglas Weinstein, M.D.

Staff Physician, Philadelphia VA Medical Center, Philadelphia, PA




Apurva Modi, M.D.Apurva Modi, M.D.

Transplant Hepatologist, Baylor All Saints Medical Center, Fort Worth, TX



Grishma Joy, M.D.Grishma Joy, M.D.

Chief, Inflammatory Bowel Disease Program, Washington Hospital Center



Erik von Rosenvinge, M.D.Erik von Rosenvinge, M.D.

Chief, Gastroenterology Section, VA Maryland Health Care System, Department of Veterans Affairs
Assistant Professor of Medicine, University of Maryland School of Medicine



Lakshmi Gopal, M.D.Lakshmi Gopal, M.D.

Practicing Gastroenterologist, Pensacola, FL




Michael Yao, M.D.Michael Yao, M.D.

Staff Clinician, Mucosal Immunity Section, Laboratory of Host Defenses, National Institute of Allergy and Infectious Diseases, National Institutes of Health



Alireza Tabesh, M.D.Alireza Tabesh, M.D.

Practicing Gastroenterologist, Los Angeles, CA