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Genetics in medicine. Genetics and medicine. The genetics of medicine. All of these reflect slightly different aspects of the integration of basic genetic principles into the practice of medicine. The genetic "revolution" that has occurred over the past 20 years has thrust clinical genetics into the mainstream of medical practice. No longer is genetics a small, poorly understood discipline tucked away in the department of pediatrics or obstetrics. Rather, every component of health care delivery requires at least a working knowledge of core genetic principles. This fact is directly reflected in changes in medical school curricula, board questions, and continuing medical education. While the vast majority of medical students will not go on to specialize in medical genetics, all of them will need to know much about genetic concepts and principles—more, perhaps, than some would like. Still, there truly is not a discipline in all of medicine that does not use genetic principles, genetic information, and genetic techniques in the practice of its field. Thus, a textbook in medical genetics must of necessity be broad and inclusive in the scope of material covered. The principles must be unifying and globally applicable. There must be sufficient detail to guide the student to successful completion of the curriculum at his/her respective medical school and to pass all three steps of the United States Medical Licensing Examination (USMLE). Most importantly, it should be a resource that students can use throughout their medical school years and beyond to refer to when questions arise during the times of residency and practice as a professional.

One caveat needs to be mentioned. The rapid pace at which genetic information is changing will require frequent and periodic updates to the information base. The printed textbook will require electronic augmentation for this generation of learners and updates to keep up with the dizzying pace of additional genetic knowledge. Any updates will be available at

This book utilizes an integrated approach to medical genetics by combining a tailored introduction to essential general genetics and up-to-date coverage of medical genetics following the curriculum recommended by the Association of Professors of Human Genetics and Medical Genetics and by the American Society of Human Genetics Guidelines. Core genetic principles are reviewed with an emphasis on mechanisms and unifying concepts.

One of the great challenges of teaching medical genetics is the tremendous diversity found in the educational background of entering medical students. Over the past decade, medical schools have purposefully sought a more diversified group of applicants. While this diversity definitely provides a more interesting—and fun—group of students, it presents a major challenge in teaching "medicine" and medical genetics in particular. One student in the class may have just finished a doctorate degree in molecular genetics while a classmate may have a liberal arts background and have taken only the minimal amount of required science courses for admission and to attain a decent score on the MCATs. Instructors can assume a student's motivation and intelligence, but undergraduate background diversity means that they cannot necessarily assume specific prior science knowledge.

With this in mind, we have organized each chapter in this book into three distinct parts:

  1. background and systems integration

  2. medical genetics, and

  3. case study applications.

The background and systems portion contain the basic genetic principles needed to understand the medical application. This information is available for any student needing to refresh themselves on the principles—or in some cases to learn it for the first time. This information draws upon principles that would have been covered in an undergraduate genetics course and utilizes abundant graphics and tabular information. It emphasizes the "why" and "how" of these principles to hopefully address the common concern voiced by many medical students, "Why do I need to know this. I'm going to be a __________." For the student with a stronger background in genetics, this section may be easily skipped; each part of the chapter is written as a stand-alone component. The "meat" of each chapter is in the second (medical genetics) part. This part contains all of the pertinent information to build a strong knowledge base for being successful on all three steps of the USMLE. The third part uses case study examples to emphasize the direct application of these facts and principles to patient care.

This book is written as a narrative that develops with subsequent chapters building upon the foundation laid by the previous chapters. Thus, the whole "story" of medical genetics could be read from cover to cover if so desired. Alternatively, each chapter is also organized to stand alone and can be accessed for specific references and topics.

As the readers work their way through the book they should be on the lookout for several recurring themes. Woven throughout the details of each chapter are the basic themes of medical genetics. Some of the most important themes to observe include:

  • Genotype to phenotype correlation(s)—the need to correlate clinical observations with information obtained by laboratory genetic techniques

    • — what is a phenotype?

    • —levels of describing a phenotype.

    • —defining endophenotypes as a critical strategy for therapy.

  • Pathogenesis—how do changes in genes translate into human medical conditions?

  • Variability (expanded phenotypes).

  • Genetic/etiologic heterogeneity–the rule, not the exception.

Without a doubt a working knowledge of genetic principles will be a necessity for all practicing health care providers regardless of their chosen specialty. We hope that you have as much fun reading this text as we did writing it. Nothing would thrill us more than to know that you took something from this book and applied it directly to your practice.

Best wishes.

G. Bradley Schaefer, MD

James N. Thompson, Jr., PhD

October 2013

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