2013-12-18 16:17:31 UTC

What is Personalized Medicine?

Dec. 20, 2013


Madhusudan Grover, MD

Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, MN



Gianrico Farrugia, MD

Division of Gastroenterology and Hepatology and Center for Individualized Medicine, Mayo Clinic, Rochester, MN


Physicians have always prided themselves in providing personalized health care. It therefore comes as a surprise to some to hear the term “personalized medicine” being used to describe a particular type of care. The term personalized medicine is currently used to describe the tailoring of medical treatment to the individual characteristics of each patient based on molecular, genomic and related –omic (pharmaco-genomics, epigenomic, proteomic, metabolomic … ) data. Other terms that are used include individualized medicine and precision medicine. Personalized medicine is about predicting, diagnosing and treating a disease based on each person’s unique clinical, genetic, genomic and environmental information. Often considered akin to “genomic” medicine, the interest in personalized medicine surged with the sequencing of the human genome in 2003.

Personalized medicine is a potentially transformational event in the practice of medicine; however, there still are considerable regulatory, reimbursement and technological hurdles to overcome before personalized medicine realizes its full potential. It is not to be confused with “genetic medicine”, which is an established field of medicine mostly examining mono-genetic disorders with more predictable and known inheritance pattern (e.g. sickle cell anemia, cystic fibrosis). Next generation sequencing techniques such as whole genome or exome sequencing and RNA-seq now allow a better understanding of more complex disorders such as cancer, heart disease and diabetes, which are believed to involve complex interactions between environmental factors and the human genome. The area that has impacted the clinical practice most at this time is pharmaco-genomics, using genomic data to deliver the right drug at the right dose at the right time, with targeted therapy for cancer also rapidly expanding. Gene panels based on next generation sequencing for disease areas (e.g. medications, cancer, cardiovascular) or specific diseases (e.g. colorectal cancer) are entering the practice at an increasing rate and will likely dominate the market for a few years before the widespread use of whole genome/exome sequencing.

The infrastructure and expertise needed to develop a personalized medicine program with application into clinical care is considerable (sequencing, conversion of huge data sets into actionable reports, calling variants as significant or not, storage and retrieval of genomic data, etc.), and this has limited personalized/individualized medicine approaches to integrated, tertiary-care academic medical centers. As our understanding of how to handle these complex and large datasets improves and as commercial entities develop a similar expertise, we will likely see diffusion of personalized/individualized medicine into primary care, especially in pharmaco-genomics, cancer care and for diagnostic dilemmas. It however is absolutely critical to realize that the terms personalized and/or individualized do not only apply to data, they equally apply to patients, well persons and their relatives. Therefore, it is critical to have an in-depth discussion with the patient, preferably by a specialized genomic counselor, before proceeding with large gene panels or whole genome/exome sequencing to share decision making as the data gained through such analysis can have profound effects on their current and future care and on the well-being of their family members.

Within gastroenterology and hepatology, already there exist examples of how personalized medicine is used today. These include the use of routine thiopurine methyltransferase phenotyping and EMR-based algorithms to guide thiopurine use in IBD, the absence or presence of human anti-chimeric antibodies in guiding anti-TNF use in IBD, and detection of IL28B polymorphisms in predicting response to pegylated interferon-α plus ribavirin treatment in hepatitis C. Additional applications from genomics include the recent introduction of a 17-gene panel for patients with suspected hereditary colon cancer and the targeting of specific chemotherapy for cholangiocarcinoma. In addition to the host genomics and epigenomics, an individual’s microbiome and study of microbiota genomics and its effect on host should also be considered as a part of personalized medicine. There is significant interest in the role of gut microbiota on various luminal and other complex disorders including obesity, diabetes, rheumatoid arthritis and many other diseases. Studies of intestinal microbiome will likely become an integral part of personalized medicine and the gastroenterology community has an opportunity to play a significant role.

We are still at the beginning of the journey to deliver personalized/individualized medicine, a journey which will likely shape medicine for the coming decades. Many challenges remain including:

  • Establishing an agreed upon depth threshold for adequate sequencing.
  • Further reductions in the cost of sequencing and bioinformatics.
  • Creating guidelines for the validation of tests based on next generation sequencing.
  • Identifying patient population likely to benefit from individualized care.
  • Generating, interpreting, visualizing and storing genome sequencing data that can be used for clinical care.
  • Developing user-friendly support tools and practice guidelines.
  • Getting insurance reimbursement for genomic testing.
  • Ethical issues surrounding routine genomic sequencing and obtaining future health-care coverage.
  • Psychological impact of having knowledge of genomic predictors and its impact on medical and personal decisions.

We believe that a careful selection of patients, diseases and drug targets will guide future research, early discovery and clinical practice. Additionally, institutional and extramural support and funding to conduct research on best ways to establish personalized medicine programs will be critical to achieve success in this area. We are privileged to be at the dawn of personalized/individualized medicine where the interface of our genomic discoveries and technological advancements are helping us realize the dream of achieving a model of medicine which is individualized to each patient and their illness.

Drs. Grover and Farrugia do not have any conflicts to disclose.


1. Shan L, Molberg O, Parrot I, et al. Structural basis for gluten intolerance in coeliac sprue. Science 2002;297:2275-2279.

2. Sollid LM and C Khosla. Novel therapies for coeliac disease. J Intern Med 2011;269:604-613.

3. Camarca A, Anderson RP, Mamone G, et al. Intestinal T cell responses to gluten peptides are largely heterogeneous: Implications for a peptide-based therapy in celiac disease. The Journal of Immunology 2009;182:4158-4166.


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