Written Assignment 2

In the best of all worlds, biotechnology would prevent humans from ever getting debilitating diseases. Next best would be to cure diseases once and for all. But these noble goals are not always possible, so biotechnology often is directed at the more practical goal of treating diseases, usually by producing medicines more efficiently and more effectively than they can be produced with traditional methods. Biotechnology has achieved some notable successes in achieving this goal. The treatment of diabetes is one such success story. (Figure 7-16) Type 1 diabetes, often called juvenile diabetes, is a chronic disease in which the body cannot produce the hormone insulin. Without insulin, the body’s cells are unable to take up and break down sugar from the blood. Type 2 diabetes, which accounts for 90% of all cases of diabetes, is a metabolic disorder characterized by elevated blood sugar levels resulting from insulin resistance and insufficient insulin production. Complications from both types of diabetes can be deadly. Approximately one-third of all people with diabetes treat their condition with one or more daily injections of insulin. As recently as 1980, the insulin necessary to treat diabetes was extracted from the pancreas of cattle or pigs that had been killed for meat. This process of collecting insulin was difficult and costly. Everything changed in 1982, when a 29-year-old entrepreneur, Bob Swanson, joined scientists Herbert Boyer and Stanley Cohen to realize the potential of recombinant DNA technology for insulin production. The team used restriction enzymes to snip out the human DNA sequence that codes for the pro-duction of insulin. They then inserted this sequence into the bacterium E. coli, creating a transgenic organism. After cloning the new, transgenic bacteria, the team was able to grow vats of the bacterial cells, all of which churned out human insulin (Figure 7-16). The drug could be produced efficiently in huge quantities and made available for patients with diabetes. This was the first genetically engineered drug approved by the FDA, and it continues to help millions of people every day.

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Several important achievements followed the development of insulin-producing bacteria. Two of these include: 1) Human growth hormone (HGH): Produced by the pituitary gland, growth hormone has

dramatic effects throughout the body. It stimulates protein synthesis, increases utilization of body fat for energy to fuel metabolism, and stimulates the growth of virtually every part of the body. Insufficient growth hormone production, usually due to pituitary malfunctioning, leads to dwarfism. When treated with supplemental HGH, individuals with dwarfism experience additional growth. HGH is also used to combat weight loss in AIDS patients. Until 1994, it was prohibitively expensive because it could only be produced by extracting and purifying it from the pituitary glands of human cadavers. Through the creation of transgenic bacteria, using a technique similar to that used in the creation of insulin-producing bacteria, human growth hormone can now be created in virtually unlimited supplies.

2) Erythropoietin: Produced primarily by the kidneys, erythropoietin (also known as EPO) regulates the production of red blood cells. Numerous clinical conditions (such as nutritional deficiencies and lung disease, among others) and treatments (such as chemotherapy) can lead to anemia, a lower than normal amount of red blood cells, which reduces an individual’s ability to transport oxygen to tissues and cells. Cloned in 1985, recombinant human erythropoietin (rhu-EPO) is now produced in large amounts in hamster ovaries. It is used to treat many forms of anemia. Worldwide sales of EPO are in the billions of dollars. EPO has been at the center of several “blood doping” scandals in professional cycling. This hormone increases the oxygen-carrying capacity of the blood, so some otherwise healthy athletes have used EPO to improve their athletic performance. It can be very dangerous, though. By increasing the number of red blood cells, the blood can become much thicker and this can increase the risk of heart attack.

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How much do you want to know about your future? If you carry a gene that means you are likely to develop a particular disease later in life, or if there is a large chance that your children will be born with a genetic disease, would you want to know? As biotechnology develops the tools to identify some of the genetic time-bombs that many of us carry, these are questions that we all must address. 1) Is a given set of parents likely to produce a baby with a genetic disease? Many genetic diseases occur only if an individual inherits two copies of the disease-causing gene, one from each parent. This is true for Tay-Sachs disease, cystic fibrosis, and sickle-cell anemia, among others. Individuals with only a single copy of the disease-causing gene never fully manifest the disease but may pass on the disease gene to their children. Consequently, two healthy parents may produce a child with the disease. In these cases, it can be beneficial for the parents to be screened to determine whether they carry a disease-causing copy of the gene. Such screening, combined with genetic counseling and testing of embryos following fertilization, can reduce the incidence of the disease dramatically. This has been the case with Tay-Sachs disease, for example. Since screening begin in 1969, the incidence of Tay-Sachs disease has been reduced by more than 75%.

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2) Will a baby be born with a genetic disease? Once fertilization has occurred, it is possible to test an embryo or developing fetus for numerous genetic problems. Prenatal genetic screening can detect disorders such as cystic fibrosis, sickle-cell anemia, Down syndrome, and others. The list of additional conditions that can be detected is growing quickly. To screen the fetus, it is necessary to sample some of the fetal cells and/or the amniotic fluid, which carries many chemicals produced by the developing embryo. This is usually done via amniocentesis or chorionic villus sampling (CVS)— techniques that we explore in detail in Chapter 8. Once collected, the cells can be analyzed using a variety of means. Let’s examine the case of SCID, which has served as a model for gene therapy. SCID is a condition in which a baby is born with an immune system unable to properly produce a type of white blood cell. This leaves the infant vulnerable to most infections and usually leads to death within the first year of life (Figure 7-19). In gene therapy for SCID, researchers removed from an affected baby’s bone marrow some stem cells, cells that have the ability to develop into any type of cell in the body. In bone marrow, they normally produce white blood cells, but in individuals with SCID, a malfunctioning gene disrupts normal white blood cell production. Next, in a test tube, the bone marrow stem cells were infected with a transgenic virus carrying the functioning gene. Ideally, the virus inserted the good gene into the DNA of the stem cells, which were then injected back into the baby’s bone marrow. There, the cells could produce normal white blood cells, permanently curing the disease. Although this strategy worked to cure several cases of SCID, treatment has been suspended indefinitely following the recent deaths of two patients from illness related to their treatment. 3) Is an individual likely to develop a genetic disease later in life? DNA technology can also be used to detect disease-causing genes in individuals that are currently healthy but are at increased risk of developing an illness later. Early detection of many diseases such as breast cancer, prostate cancer, and skin cancer can greatly enhance the ability to treat the disease, and can reduce the risk of more severe illness or death.

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Difficulties with gene therapy have been encountered in several different areas, usually related to the organism used to transfer the normal-functioning gene into the cells of a person with a genetic disease. Beyond the technical problems listed on the slide above—some of which may benefit from the CRISPR system described in Section 7-3—the malfunctioning gene has not been identified for most diseases, or the disease is caused by more than one malfunctioning gene. Additionally, it is important to keep in mind that gene therapy targets cells in the body other than sperm and eggs. Consequently, while a disease might, in theory, be cured in the individual receiving the therapy, he or she can still pass on the disease-causing gene(s) to offspring. It’s not clear what the future holds for gene therapy, but a great deal of research is in progress.

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Cloning. Perhaps no scientific word more easily conjures horrifying images of the intersection of curiosity and scientific achievement. But is fear the appropriate emotion to feel about this burgeoning technology? Perhaps not. For starters, let’s clarify what the word means. Cloning actually refers to a variety of different techniques. To be sure, cloning can refer to the creation of new individuals that have exactly the same genome as the donor individual—a process called “whole organism cloning.” That is, a clone is like an identical twin, except that it may differ in age by years or even decades. It is also possible to clone tissues (such as skin) and entire organs from an individual’s cells. Cloning took center stage in the public imagination in 1997, when Ian Wilmut, a British scientist, and his colleagues first reported that they had cloned a sheep—which they named Dolly. Their research was based on ideas that went back to 1938, when Hans Spemann first proposed the experiment of removing the nucleus from an unfertilized egg and replacing it with the nucleus from the cell of a different individual. Although the process used by Wilmut and his research group was difficult and inefficient, it was surprisingly simple in concept. They removed a cell from the mammary gland of a grown sheep, put its nucleus into another sheep’s egg from which the nucleus had been removed, induced the egg to divide, and transplanted it into the uterus of a surrogate mother sheep. Out of 272 tries, they achieved just one success. But that was enough to show that the cloning of an adult animal was possible. Shortly after news of Dolly’s birth, teams set about cloning a variety of other species including mice, cows, pigs, and cats. Not all of this work was driven by simple curiosity. For farmers, cloning could have real value. It can take a long time to produce animals with desirable traits from an agricultural perspective—such as increased milk production in cows. And with each successive generation of breeding, it can be difficult to maintain these traits in the population. But through the process of transgenic techniques and whole-animal cloning, large numbers of the valuable animals with such traits can be produced and maintained. At this point, it is almost certain that the cloning of a human will be possible. There is near unanimity among scientists that human cloning to produce children should not be attempted.

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