The parents of a 2-year-old girl write that their daughter “could die within the next year” because a genetic mutation is causing her heart to fail.

“Time is quickly running out for me,” writes a man in his mid-30s whose DNA harbors a genetic mistake certain to destroy his brain within a matter of years.

“Watching my sons disintegrate before my eyes is heartbreaking,” writes a mother with two children affected by a faulty gene that affects cognition, speech and mobility. One of her sons, she writes, is still walking and in college, but “it is only a matter of time before he will be in a wheelchair and his cognition will decline.”

Stories of human tragedies like these arrive in my inbox with increasing, painful regularity. People write to see if I can build a medication to fix their genes and stave off an early, imminent death. Their wish is not futuristic: Many scientists, including me, build DNA fixes for a living.

Over the past decade, thousands of people have agreed to be genetically engineered in experimental trials to develop these treatments — and to save their lives. Famously proposed 50 years ago, such fixes, or ‌gene therapies, began earnest development in 1989. After fits and starts, the first real cures for children born with no functioning immune system arrived in the early 2000s.

Several approved gene therapy medicines now exist. All involve taking a virus, replacing its harmful contents with a disease-treating gene, and injecting it into a person (or exposing the person’s cells to that virus in a dish and putting them back). Though effective, these treatments remain cumbersome to build and jaw-droppingly expensive: One recently approved gene therapy for people with an inherited bleeding disorder costs a record-breaking $3.5 million for a single-use vial, making it the most expensive drug in the world.

Gene editing is much newer technology and builds on the gains of gene therapy. Instead of using a virus, however, gene editing relies on a molecular machine called CRISPR, which can be instructed to repair a mutation in a gene in nearly any organism, right where that “typo” occurs. Impressively versatile, potential applications for CRISPR range from basic science to agriculture and climate change. In medicine, CRISPR gene editing allows physicians to directly fix typos in the patients’ DNA. And so much substantive progress has been made in the field of genetic medicine that it’s clear scientists have now delivered on a remarkable dream: word-processor-like control over DNA.

The first person to be gene-edited with CRISPR was treated only three years ago for a disorder of red blood cell production, and since then, the technology has been used to treat congenital blindness, sickle cell disease, heart disease, nerve disease, cancer and H.I.V. While not all diseases have a single-gene basis, most have a genetic component. Early studies suggest that conditions like heart disease, chronic pain and Alzheimer’s disease could all be treated with CRISPR. ‌Dr. Jennifer Doudna, a winner of the 2020 Nobel Prize in Chemistry for CRISPR gene editing along with Dr. Emmanuelle Charpentier, aptly described it as a “profound opportunity to change health care for many people.”

Scientists like me can now visualize an ideal scenario for the future of CRISPR medicines: When a 3-month-old starts to develop antibiotic-resistant infections, her primary care doctor orders a DNA test, and 48 hours later, ‌‌the faulty gene that is preventing the development of a normal immune system is identified. “Not a problem. We will refer your child for corrective CRISPR therapy,” says the physician to the devastated parents. “The treatment will be covered by insurance and take all of two months.”

Here’s what will happen in those two months: A dedicated CRISPR ‌cures ‌‌center at a university-affiliated hospital then takes the diagnosis and morphs it into an order form for a manufacturing facility to create the medication that will repair the faulty gene. After a month of testing and data review by hospital clinicians and university scientists, the physician does a simple IV injection of the resulting CRISPR medicine, and after a three-day stay at the hospital to confirm‌ the gene editing went according to plan, the child is sent home.

Just as CRISPR once seemed to be something out of science fiction, so might everything in the preceding paragraphs — but every step of that process is technically feasible today.

Examples from across the world illustrate the possibilities of what CRISPR can accomplish. In China, it was recently used to treat two children ages 7 and 8 with a genetic condition related to sickle cell disease called beta-thalassemia. Before treatment, the children were unable to create normal red blood cells and required blood transfusions every two to three weeks. Within a month after they received gene-edited cells, the transfusions ended. Eighteen months later, the children remained free of disease symptoms.

In the United States and in Europe, progress has also been formidable. The biotechnology companies CRISPR Therapeutics and Vertex have cured 31 people with sickle cell disease, who no longer experience the debilitating episodes of pain that characterize their condition. Another biotechnology company, Intellia Therapeutics, teamed up with Regeneron and used CRISPR to inactivate a typo-laden toxic gene in the livers of 15 people. A mere month after this injection, 93 percent of the toxin was gone from the bloodstreams of patients who received the highest dose of CRISPR medicine. Verve Therapeutics is developing a CRISPR treatment for heart disease, with an initial focus on a severe genetic form. Should Verve meet its ambitious goal of expanding this approach to patients with the common type of heart disease, one gene edit could replace daily medications such as statins. Physicians elsewhere are using CRISPR to test a treatment for people who carry H.I.V. by cutting out the virus’s DNA from their immune system. If they succeed, it’s possible that about 40 million people could benefit.

But the question is: Will they?

There are up to 400 million people worldwide affected by one of the 7,000 diseases caused by mutations in single genes. ‌Scientists owe them and their families honesty about the ‌‌chasm between a test tube in a lab and an IV line in a hospital. The greatest obstacles are not technical but legal, financial and organizational.