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Personalized Medicine 101

The Science   

Humans are unique individuals. With the exception of identical twins, this is true of our genomes as well. Though all of us are genetically very similar, there are small differences in our DNA that are unique — and which make us unique in terms of health, disease and our response to certain treatments.  

The natural variations (DNA polymorphisms) found in our genes play a role in our risk of getting or not getting certain diseases. The combination of these variations across several genes — along with numerous external factors such as environment, diet and exercise — affect each individual’s risk. Natural genetic variations also are part of the reason that the same drug works well in one individual and not another. Variations in DNA can lead to differences in how drugs are absorbed, metabolized and used by the body. Understanding these genetic variations and their interactions with environmental factors will help researchers produce better predictive and diagnostic molecular tests and drugs, and will help physicians better select treatments and dosing based on individual need.  

The vast majority of genes function exactly as intended: giving rise to proteins that play key roles in biological processes and allow a person to grow and live in his/her environment. In rare instances, one single mutated or malfunctioning gene leads to a distinct genetic disease or syndrome. The most familiar of these rare disorders include sickle cell anemia, cystic fibrosis and Huntington’s disease. Such disorders are termed “monogenic” because a single gene is responsible for their occurrence. But multiple genes acting together can also influence the development of many common and complex diseases, as well as our response to the pharmaceuticals designed to treat them. The contribution of several genes to these complex disorders is termed “polygenic.”  

Often as a result of this complexity, what may appear to be one disease on a clinical level could, on a molecular level, be reclassified as several different diseases, each of which might respond to a different treatment. Such disease complexity exists for asthma and many forms of cancer. Through molecular analysis of “biomarkers” — biological molecules that indicate a particular disease state — scientists can identify these sub-types within a disease. Biomarker analysis can also help classify sub-groups of patients who have the same molecular variation of the disease, enabling one to monitor its progression, select appropriate treatments, and measure the patient’s response to medication.  

Until recently, many technologies for examining DNA, proteins and other biomarkers were slow and expensive, which limited the scope and impact of molecular analysis. But new technologies, such as microarrays and protein arrays, are making biomarker detection much faster and more affordable. Future advances may make it feasible for physicians to screen patients for relevant molecular variations in the office prior to prescribing a particular drug.  

Read about the promise of personalized medicine.

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