In early 2021, Dr. Michael Ombrello, an investigator at the National Institutes of Health, received a message from doctors at Yale about a patient with a novel genetic mutation—the first of its kind ever seen. A specialist in rare inflammatory and immune disorders, Ombrello was concerned by what first-round genetic tests showed: a disabling mutation in a gene, known as PLCG2, that’s crucial for proper immune functioning. It was hard to discern how the patient, a forty-eight-year-old woman, had survived for so long without serious infections. Even more puzzling was the sudden onset of severe joint pain and swelling she was experiencing after years of excellent health. He decided to bring her to the N.I.H. campus, in Bethesda, Maryland, to study her case first hand.

That’s how I ended up as a patient in his clinic on a sweet, warming day in April, 2021, just as the cherry blossoms in the Washington area were in full bloom. As a historian and a biographer, I am used to conducting research, examining other people’s lives in search of patterns and insights. That spring, I became the research subject. At the N.I.H., Ombrello’s team took twenty-one vials of my blood and stored a few of them in liquid nitrogen for future use. Scientists outside the N.I.H. began to study me, too. In the past few years, my case has been examined by specialists at Yale, Harvard, Columbia, and the University of Pennsylvania—by immunologists, rheumatologists, dermatologists, pulmonologists, and experts in infectious disease. It has been debated at hospital grand rounds and global medical conferences, and in high-powered conference calls. There are PowerPoint decks about it.

All of which makes me lucky, in one respect. Far too often, women who present with hard-to-diagnose illnesses are told that the symptoms are no big deal, that the problem is in their head. They spend years going from doctor to doctor, in a desperate search for someone, anyone, who’s willing to help. This has not been my experience. From the first, doctors took my condition seriously, sometimes more seriously than I did. They pushed me along to the nation’s greatest experts, at the finest medical institutions. My insurance paid large sums for tests and treatments; my family and friends were patient and supportive. All the while, I was able to keep doing what needed to be done: write a book, raise a child, teach my classes.

But none of this gets around a single, stubborn fact. “You are the only person known to have this exact mutation,” Ombrello explains. “I haven’t seen any reports in reference populations of this mutation, and I don’t have anyone that I’ve had referred to me or that I’ve seen in my patient cohort that has this mutation.” In other words, I am one of a kind, and therefore a medical curiosity. Doctors often blurt out that my situation is “fascinating” before catching themselves; they’re aware that nobody really wants to be fascinating in quite this way. Thanks to advances in genetic sequencing, though, researchers are increasingly able to identify one-offs like me.

That leaves them engaged in a process not so different from what I do as a biographer, trying to understand a life and its meaning based on deep research but incomplete information. My historical training pushes me to think in chronological terms: Where do we stand in the great saga of human history? How do grand structural forces and ideas and technologies shape what it’s like for an individual to live a life, day to day? But nothing has rooted me in history quite like the experience of getting sick. Though illness and death may be the universals of earthly existence, the way that we get sick—and, sometimes, get better—has everything to do with the luck of the moment.