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6.1: Case Study - Why do we need to sequence everybody's genome?

  • Page ID
    22473
  • Case Study: Pharmacogenomics, a personalized medicine

    Steve is a 50-year-old morbidly obese male. He has high blood pressure and cardiovascular disease. Recently, he lost 10 pounds of weight in a month without trying. He also gets thirsty very easily and makes frequent visits to the restroom. His doctor diagnosed him with insulin-dependent type 2 diabetes after some physical and blood tests. The type 2 diabetes, also called diabetes mellitus, is a condition in which either the beta cells of a person’s pancreas stop secreting insulin due to the high demand of insulin by an overweight person, or the body cells become insensitive to insulin. Insulin is a hormone that activates all the cells of the body to uptake glucose from the bloodstream. Cells need glucose to acquire energy (ATP) through cellular respiration to perform various metabolic activities. High levels of blood glucose in the absence of insulin may lead to high blood glucose and eventually may lead to the symptoms that Steve is experiencing.

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    Figure \(\PageIndex{1}\): Personalized Medicine is the long tail of Health Care (CC BY 2.0 Generic; Mark Scrimshire via Flickr).

    Steve’s doctor prescribed gliclazide. Gliclazide belongs to the sulfonylurea category of drugs. Sulfonylureas stimulate the beta cells of the pancreas to secrete insulin. Steve started this treatment and experienced an adverse reaction after taking his second dose. He experienced feelings of hunger, sweating, shakiness, and weakness a few minutes after taking the medication. He called 911. When he recovered, he went back to his doctor. His doctor told him that he had experienced hypoglycemia, which is one of the major side effects of sulfonylurea-based medicines. The doctor noted that due to the other complications that Steve has, such as cardiovascular disease, gliclazide was the best choice. The doctor explained that not everyone responds to medications in the same way. A drug that works well for one person may not be effective for another. The dose of a drug that cures a disease in one individual may be inadequate for someone else. Some people may experience side effects from a given medication, whereas other people do not. This variation in responses to medications can be due to differences in our genes. That’s where the field of pharmacogenetics comes in. News media have hailed it as the "new frontier in medicine." It certainly seems to hold promise for improving pharmaceutical treatment of patients.

    Pharmacogenomics is based on a special kind of genetic testing. It looks for small genetic variations that influence a person’s ability to activate and deactivate drugs. Results of the tests can help doctors choose the best drug and most effective dose for a given patient. Many drugs need to be activated by the patient’s own enzymes, and inherited variations in enzymes may affect how quickly or efficiently this happens. For example, if a patient’s enzymes break down a particular drug too slowly, then standard doses of the drug may not work very well for that patient. Drugs also must be deactivated to reduce their effects on healthy cells. If a patient’s enzymes deactivate a drug too slowly, then the drug may remain at high levels and cause side effects. Steve experienced a high release of insulin due to the variations in his genotype.

    The doctor recommended that Steve goes through genetic testing for a better treatment plan. One of the main benefits of pharmacogenomics is greater patient safety. Pharmacogenomic testing may help identify patients who are likely to experience adverse reactions to drugs so that different, safer drugs can be prescribed. Another benefit of pharmacogenomics is eliminating the trial-and-error approach that is often used to find appropriate medications and doses for a given patient. This saves time and money as well as improving patient outcomes. This is more like a personalized medicine as demonstrated in the picture above.

    Because pharmacogenomics is a new field, some insurance companies do not cover it, and it can be very expensive. Also, not all of the genetic tests are yet widely available. In addition, there may be ethical and legal issues associated with genetic testing, including concerns about privacy issues. Because Steve has all these concerns, he has many questions for his doctor.

    In order to understand personalized medicine, we need to know what genes do, how they interact and learn all the differences in DNA between people. As you read this chapter, think about how an understanding of the human genome and genetics is essential for discovering how medicines may affect each of us individually.

    As you read this chapter, try to answer the following questions:

    • What is a gene?
    • Enzymes are proteins. How are enzymes synthesized?
    • What is the relationship between an enzyme and DNA?
    • Why do people differ genetically?
    • How are the genes sequenced?
     

    Chapter overview: in this chapter, you will learn the following:

    • How genes, and their different alleles, are located on chromosomes.
    • The 23 pairs of human chromosomes, which include autosomal and sex chromosomes.
    • How DNA was discovered to be the inherited genetic material.
    • The structure of DNA and how DNA replication occurs.
    • The central dogma of molecular biology, which describes how DNA is transcribed into RNA, and then translated into proteins.
    • The structure, functions, and possible evolutionary history of RNA.
    • How genes code for proteins using codons made of the sequence of nitrogen bases within RNA and DNA.
    • How proteins are synthesized through the transcription of RNA from DNA and the translation of protein from RNA, including how RNA and proteins can be modified, and the roles of the different types of RNA.
    • What mutations are, what causes them, different specific types of mutations, and the importance of mutations in evolution and to human health.
    • How the expression of genes into proteins is regulated and why problems in this process can cause diseases such as cancer.
    • What is Biotechnology and how it is applied?
    • What is Pharmacogenomics?