The Gene

by Siddhartha Mukherjee

  The leap in size was not just a quantitative barrier; to succeed, the gene cloners would need to use new cloning technologies. Both the somatostatin and insulin genes had been created from scratch by stitching together bases of DNA—A added chemically to the G and the C and so forth. But the factor VIII gene was far too large to be created using DNA chemistry. To isolate the factor VIII gene, both Genentech and GI would need to pull the native gene out of human cells, spooling it out as if extracting a worm from the soil.

  But the “worm” would not come out easily, or intact, from the genome. Most genes in the human genome are, recall, interrupted by stretches of DNA called introns, which are like garbled stuffers placed in between parts of a message. Rather than the word genome, the actual gene reads gen . . . . . . . . . om . . . . . . e. The introns in human genes are often enormous, stretching across vast lengths of DNA, making it virtually impossible to clone a gene directly (the intron-containing gene is too long to fit into a bacterial plasmid).

  Maniatis found an ingenious solution: he had pioneered the technology to build genes out of RNA templates using reverse transcriptase, the enzyme that could build DNA from RNA. The use of reverse transcriptase made gene cloning vastly more efficient. Reverse transcriptase made it possible to clone a gene after the intervening stuffer sequences had been snipped off by the cell’s splicing apparatus. The cell would do all the work; even long, unwieldy, intron-interrupted genes such as factor VIII would be processed by the cell’s gene-splicing apparatus and could thus be cloned from cells.

  By the late summer of 1983, using all the available technologies, both teams had managed to clone the factor VIII gene. It was now a furious race to the finish. In December 1983, still running shoulder to shoulder, both groups announced that they had assembled the entire sequence and inserted the gene into a plasmid. The plasmid was then introduced into hamster-derived ovary cells known for their ability to synthesize vast quantities of proteins. In January 1984, the first cargoes of factor VIII began to appear in the tissue-culture fluid. In April, exactly two years after the first AIDS clusters had been reported in America, both Genentech and GI announced that they had purified recombinant factor VIII in test tubes—a blood-clotting factor untainted by human blood.

  In March 1987, Gilbert White, a hematologist, conducted the first clinical trial of the hamster-cell-derived recombinant factor VIII at the Center for Thrombosis in North Carolina. The first patient to be treated was G.M., a forty-three-year-old man with hemophilia. As the initial drops of intravenous liquid dripped into his veins, White hovered anxiously around G.M.’s bed, trying to anticipate reactions to the drug. A few minutes into the transfusion, G.M. stopped speaking. His eyes were closed; his chin rested on his chest. “Talk to me,” White urged. There was no response. White was about to issue a medical alert when G.M. turned around, made the sound of a hamster, and burst into laughter.

  News of G.M.’s successful treatment spread through a desperate community of hemophiliacs. AIDS among hemophiliacs had been a cataclysm within a cataclysm. Unlike gay men, who had quickly organized a concerted, defiant response to the epidemic—boycotting bathhouses and clubs, advocating safe sex, and campaigning for condoms—hemophiliacs had watched the shadow of the illness advance with numb horror: they could hardly boycott blood. Between April 1984 and March 1985, until the first test for virally contaminated blood was released by the FDA, every hemophiliac patient admitted to a hospital faced the terrifying choice of bleeding to death or becoming infected with a fatal virus. The infection rate among hemophiliacs during this period was staggering: among those with the severe variant of the disease, 90 percent would acquire HIV through contaminated blood.

  Recombinant factor VIII arrived too late to save the lives of most of these men and women. Nearly all the HIV-infected hemophiliacs from the initial cohort would die of the complications of AIDS. Even so, the production of factor VIII from its gene broke important conceptual ground—although it was tinged with peculiar irony. The fears of Asilomar had been perfectly inverted. In the end, a “natural” pathogen had unleashed havoc on human populations. And the strange artifice of gene cloning—inserting human genes into bacteria and then manufacturing proteins in hamster cells—had emerged as potentially the safest way to produce a medical product for human use.

  It is tempting to write the history of technology through products: the wheel; the microscope; the airplane; the Internet. But it is more illuminating to write the history of technology through transitions: linear motion to circular motion; visual space to subvisual space; motion on land to motion in air; physical connectivity to virtual connectivity.

  The production of proteins from recombinant DNA represented one such crucial transition in the history of medical technology. To understand the impact of this transition—from gene to medicine—we need to understand the history of medicinal chemicals. Stripped to its bare essence, a medicinal chemical—a drug—is nothing more than a molecule that enables a therapeutic change in human physiology. Medicines can be simple chemicals—water, in the right context and at the right dose, is a potent drug—or they can be complex, multidimensional, many-faced molecules. They are also astoundingly rare. Although there are seemingly thousands of drugs in human usage—aspirin alone comes in dozens of variants—the number of molecular reactions targeted by these drugs is a minuscule fraction of the total number of reactions. Of the several million variants of biological molecules in the human body (enzymes, receptors, hormones—and so forth), only about 250—0.025 percent—are therapeutically modulated by our current pharmacopeia. If human physiology is visualized as a vast global telephone network with interacting nodes and networks, then our current medicinal chemistry touches only a fraction of a fraction of its complexity; medicinal chemistry is a pole operator in Wichita tinkering with a few lines in the network’s corner.

  The paucity of medicines has one principal reason: specificity. Nearly every drug works by binding to its target and enabling or disabling it—turning molecular switches on or off. To be useful, a drug must bind to its switches—but to only a selected set of switches; an indiscriminate drug is no different from a poison. Most molecules can barely achieve this level of discrimination—but proteins have been designed explicitly for this purpose. Proteins, recall, are the hubs of the biological world. They are the enablers and the disablers, the machinators, the regulators, the gatekeepers, the operators, of cellular reactions. They are the switches that most drugs seek to turn on and off.

  Proteins are thus poised to be some of the most potent and most discriminating medicines in the pharmacological world. But to make a protein, one needs its gene—and here recombinant DNA technology provided the crucial missing stepping-stone. The cloning of human genes allowed scientists to manufacture proteins—and the synthesis of proteins opened the possibility of targeting the millions of biochemical reactions in the human body. Proteins made it possible for chemists to intervene on previously impenetrable aspects of our physiology. The use of recombinant DNA to produce proteins thus marked a transition not just between one gene and one medicine, but between genes and a novel universe of drugs.

  On October 14, 1980, Genentech sold 1 million of its shares to the public, provocatively listing itself at the stock exchange under the trading symbol GENE. This initial sale would rank among the most dazzling debuts of any technology company in Wall Street history: within a few hours, the company had generated $35 million in capital. By then, the pharmaceutical giant Eli Lilly had acquired the license to produce and sell recombinant insulin—called Humulin, to distinguish it from cow and pig insulin—and was rapidly expanding its market. Sales rose from $8 million in 1983 to $90 million in 1996 to $700 million in 1998. Swanson—“a short, chunky chipmunk-cheeked thirty-six-year-old,” as Esquire magazine described him—was now a millionaire several times over, as was Boyer. A graduate student who had held on to a few throwaway shares for helping to clone the somatostatin gene over the summer of 1977 woke up one morning and found himse
lf a newly minted multimillionaire.

  In 1982, Genentech began to produce human growth hormone—HGH—used to treat certain variants of dwarfism. In 1986, biologists at the company cloned alpha interferon, a potent immunological protein used to treat blood cancers. In 1987, Genentech made recombinant TPA, a blood thinner to dissolve the clots that occur during a stroke or a heart attack. In 1990, it launched efforts to create vaccines out of recombinant genes, beginning with a vaccine against hepatitis B. In December 1990, Roche Pharmaceuticals acquired a majority stake in Genentech for $2.1 billion. Swanson stepped down as the chief executive; Boyer left his position as vice president in 1991.

  In the summer of 2001, Genentech launched its physical expansion into the largest biotech research complex in the world—a multiacre stretch of glass-wrapped buildings, rolling greens, and Frisbee-playing research students that is virtually indistinguishable from any university campus. At the center of the vast complex sits a modest bronze statue of a man in a suit gesticulating over a table to a scientist in flared jeans and a leather vest. The man is leaning forward. The geneticist looks puzzled and is gazing distantly over the man’s shoulder.

  Swanson, unfortunately, was not present for the formal unveiling of the statue commemorating his first meeting with Boyer. In 1999, at age fifty-two, he was diagnosed with glioblastoma multiforme, a brain tumor. He died on December 6, 1999, at home in Hillsborough, a few miles from Genentech’s campus.

  * * *

  I. Minkowski does not recollect this, but others present in the lab have written about the urine-as-treacle experiment.

  II. They later added other collaborators, including Richard Scheller, from Caltech. Boyer put two researchers, Herbert Heyneker and Francisco Bolivar, on the project. The City of Hope added another DNA chemist, Roberto Crea.

  III. Genentech’s strategy for the synthesis of insulin was also critical to its relative exemption from Asilomar’s protocols. In the human pancreas, insulin is normally synthesized as a single contiguous protein and then cut into two pieces, leaving just a narrow cross-linkage. Genentech, in contrast, had chosen to synthesize the two chains of insulin, A and B, as separate, individual proteins and link them together afterward. Since the two separate chains used by Genentech were not “natural” genes, the synthesis did not fall under the federal moratorium that restricted the creation of recombinant DNA with “natural” genes.

  PART FOUR

  * * *

  “THE PROPER STUDY OF MANKIND IS MAN”

  Human Genetics

  (1970–2005)

  Know then thyself, presume not God to scan;

  The proper study of mankind is man.

  —Alexander Pope, Essay on Man

  How beauteous mankind is! O brave new world,

  That has such people in’t!

  —William Shakespeare, The Tempest, act 5, scene 1

  The Miseries of My Father

  ALBANY: How have you known the miseries of your father?

  EDGAR: By nursing them, my lord.

  —William Shakespeare, King Lear, act 5, scene 3

  In the spring of 2014, my father had a fall. He was sitting on his favorite rocking chair—a hideous, off-kilter contraption that he had commissioned from a local carpenter—when he tipped over the back and fell off (the carpenter had devised a mechanism to make the chair rock, but had forgotten to add a mechanism to stop the chair from rocking over). My mother found him facedown on the veranda, his hand tucked under his body unnaturally, like a snapped wing. His right shoulder was bathed in blood. She could not pull his shirt over his head, so she took a pair of scissors to it, while he screamed in pain from his wound, and in deeper agony at having a perfectly intact piece of clothing ripped to shreds before his eyes. “You could have tried to save it,” he later groused as they drove to the emergency room. It was an ancient quarrel: his mother, who had never had five shirts for all five boys at a time, would have found a way to rescue it. You could take a man out of Partition, but you could not take Partition out of the man.

  He had gashed the skin on his forehead and broken his right shoulder. He was—like me—a terrible patient: impulsive, suspicious, reckless, anxious about confinement, and deluded about his recovery. I flew to India to see him. By the time I arrived home from the airport, it was late at night. He was lying in bed, looking vacantly at the ceiling. He seemed to have aged suddenly. I asked him if he knew what day it was.

  “April twenty-fourth,” he said correctly.

  “And the year?”

  “Nineteen forty-six,” he said, then corrected himself, groping for the memory: “Two thousand six?”

  It was a fugitive memory. I told him it was 2014. Nineteen forty-six, I noted privately, had been another season of catastrophe—the year that Rajesh had died.

  Over the next days, my mother nursed him back to health. His lucidity ebbed back and some of his long-term memory returned, although his short-term memory was still significantly impaired. We determined that the rocking-chair accident was not as simple as it had sounded. He had not tipped backward but had attempted to get up from the chair, then lost his balance and shot forward, unable to catch himself. I asked him to walk across the room and noticed that his gait had an ever-so-slight shuffle. There was something robotic and constrained in his movements, as if his feet were made of iron, and the floor had turned magnetic. “Turn around quickly,” I said, and he almost fell forward again.

  Late that night, another indignity occurred: he wet his bed. I found him in the bathroom, bewildered and ashamed, clutching his underwear. In the Bible, Ham’s descendants are cursed because he stumbles on his father, Noah, drunken and naked, his genitals exposed, lying in a field in the half-light of dawn. In the modern version of that story, you encounter your father, demented and naked, in the half-light of the guest bathroom—and see the curse of your own future, illuminated.

  The urinary incontinence, I learned, had been occurring for a while. It had begun with the feeling of urgency—the inability to hold back once the bladder was half-full—and progressed to bed-wetting. He had told his doctors about it, and they had waved it off, vaguely attributing it to a swollen prostate. It’s all old age, they had told him. He was eighty-two. Old men fall. They lose their memory. They wet their beds.

  The unifying diagnosis came to us in a flash of shame the next week when he had an MRI of his brain. The ventricles of the brain, which bathe the brain in fluid, were swollen and dilated, and the tissue of the brain had been pushed out to the edges. The condition is called normal pressure hydrocephalus (NPH). It is thought to result from the abnormal flow of fluid around the brain, causing a buildup in the ventricles—somewhat akin to the “hypertension of the brain,” the neurologist explained. NPH is characterized by an inexplicable classic triad of symptoms—gait instability, urinary incontinence, dementia. My father had not fallen by accident. He had fallen ill.

  Over the next few months, I learned everything I could about the condition. The illness has no known cause. It runs in families. One variant of the illness is genetically linked to the X chromosome, with a disproportionate predominance for men. In some families, it occurs in men as young as twenty or thirty. In other families, only the elderly are affected. In some, the pattern of inheritance is strong. In others, only occasional members have the illness. The youngest documented familial cases are in children four or five years old. The oldest patients are in their seventies and eighties.

  It is, in short, quite likely to be a genetic disease—although not “genetic” in the same sense as sickle-cell anemia or hemophilia. No single gene governs the susceptibility to this bizarre illness. Multiple genes, spread across multiple chromosomes, specify the formation of the aqueducts of the brain during development—just as multiple genes, spread across multiple chromosomes, specify the formation of the wing in a fruit fly. Some of these genes, I learned, govern the anatomical configurations of the ducts and vessels of the ventricles (as an analogue, consider how “pattern-formation” genes ca
n specify organs and structures in flies). Others encode the molecular channels that transmit fluids between the compartments. Yet other genes encode proteins that regulate the absorption of fluids from the brain into the blood, or vice versa. And since the brain and its ducts grow in the fixed cavity of the skull, genes that determine the size and shape of the skull also indirectly affect the proportions of the channels and the ducts.

  Variations in any of these genes may alter the physiology of the aqueducts and ventricles, changing the manner in which fluid moves through the channels. Environmental influences, such as aging or cerebral trauma, interpose further layers of complexity. There is no one-to-one mapping of one gene and one illness. Even if you inherit the entire set of genes that causes NPH in one person, you may still need an accident or an environmental trigger to “release” it (in my father’s case, the trigger was most likely his age). If you inherit a particular combination of genes—say, those that specify a particular rate of fluid absorption with those that specify a particular size of the aqueducts—you might have an increased risk of succumbing to the illness. It is a Delphic boat of a disease—determined not by one gene, but by the relationship between genes, and between genes and the environment.

  “How does an organism transmit the information needed to create form and function to its embryo?” Aristotle had asked. The answer to that question, viewed through model organisms such as peas, fruit flies, and bread molds, had launched the discipline of modern genetics. It had resulted, ultimately, in that monumentally influential diagram that forms the basis of our understanding of information flow in living systems:

  But my father’s illness offers yet another lens by which we might view how hereditary information influences the form, function, and fate of an organism. Was my father’s fall the consequence of his genes? Yes and no. His genes created a propensity for an outcome, rather than the outcome itself. Was it a product of his environment? Yes and no. It was the chair, after all, that had done it—but he had sat on that same chair, without event, for the good part of a decade before an illness had tipped him (literally) over an edge. Was it chance? Yes: Who knew that certain pieces of furniture, moved at certain angles, are designed to jettison you forward? Was it an accident? Yes, but his physical instability virtually guaranteed a fall.