For those who want their hearts broken, the story of Zohar and Gabi Ilinetsky, the parents of one-year-old twins, is a world to live inside. Zohar: twenty-seven, confident, and voluble, a construction project manager proud of his work. Gabi: fastidious, attentive, academic, an early-education specialist who used to work at a preschool. They met in Israel, where he grew up, and settled in the San Francisco Bay Area, her childhood home. While dating, they would speak often about the parenting styles that they hoped to have. “We’re old-school people,” Zohar told me recently. “My friends now are waiting until thirty-five to start thinking about kids, but always we knew we were going to get married. We knew we were going to have children.”

To their delight, Gabi gave birth to twins: a boy, a girl. They called the children Yoel and Yael. Zohar, who does not believe in baby talk, had long, one-sided conversations with his newborn children, in Hebrew; he thought that they could understand him, or soon would. Before long, his son did the most precocious thing an infant can and rolled over. It was while watching Yoel roll on the floor one day, chatting to him as if to a middle-aged man, that Zohar noticed a fleeting peculiarity in his son’s eyes, which seemed to flicker back and forth, like the pupils of somebody trying to read a subway-station sign through the window of a moving train.

Until then, doctors had assured the Ilinetskys that the babies were healthy. Gabi took Yoel to the pediatrician, who told her not to worry, that Yoel seemed fine. But Gabi worried. She went to a second pediatrician, and a third. The Ilinetskys buy family insurance through the Kaiser Permanente network, and it costs them about fifteen hundred dollars a month. Against the pediatricians’ counsel, Gabi demanded a referral to a specialist, and Yoel underwent an MRI and other tests. At four months, he was given a diagnosis of Canavan disease, which causes rapid degeneration of the brain and, almost always, death in childhood. For a while, his parents were in shock. “After shock,” Zohar said, “comes depression.”

Infants born with Canavan seem normal at first, but they lack an enzyme crucial for the growth of white matter, the myelin layer that protects and connects neurons in the brain. Signals cross—Yoel had his first seizure at ten weeks—and motor control decays. Canavan babies typically lose the ability to hold their heads up. Their intellectual development falls off; they never learn to talk. Before long, a thickening agent had to be added to Yoel’s bottles, because his weakening swallow and gag reflexes made him prone to choking. He had to be vigilantly burped, because his digestive tract lacked normal muscle activity. The recessive gene for Canavan, as for the better-known Tay-Sachs disease, crops up most often in the Ashkenazi Jewish population, and Gabi and Zohar found that they were both carriers—meaning that any children they conceived would have a one-in-four chance of being born with the disease. With Yoel, some signs had always been there: his precocious rolling, for example, came from spastic tensing in his muscles. But now the Ilinetskys worried about Yael.

Testing showed that Yael had Canavan, too. Until then, the Ilinetskys had thought of themselves as a couple with two children, one with special needs and one without. Now they were facing the terminal brain decay of both kids. Through their own research, the Ilinetskys found a physical-therapy program called NeuroMovement, which purports to cultivate brain plasticity. Six days a week, Gabi drove the twins two hours across the Bay, from Concord to Marin County, for an hour and a half of treatment, and then drove back.

The Ilinetskys said that the therapy shows signs of success: Yael can reach out, grab toys, and do other things that many Canavan babies can’t, and Yoel seems more alert. Beyond the daily therapy, Zohar and Gabi have pinned their hopes on a gene-replacement treatment being developed by Paola Leone, a neuroscientist at Rowan University, in New Jersey. Leone’s team aims to replace the mutated gene in Canavan patients with a normal version, packaged in a special virus that “infects” primarily white-matter cells. The procedure, one of several gene-therapy protocols in development for Canavan patients, has been effective in rodents; it is awaiting funding and F.D.A. approval to enter Phase I trials.

For the Ilinetskys, the challenge was cost. They pay three thousand dollars a week for NeuroMovement, which is considered experimental and therefore isn’t covered by insurance. Leone, meanwhile, needs $3.5 million to fund a clinical trial of her treatment for a group of Canavan children, potentially including Yoel and Yael. Frustrated with the system, the Ilinetskys decided to go outside it. “We thought maybe we could buy a few thousand lottery tickets,” Zohar said, grimly.

Instead, in December, they requested two million dollars on the Internet fund-raising platform GoFundMe. “We need your help,” Gabi wrote on their campaign page, which included pleas in Hebrew, Russian, and Spanish. Through donations mostly from strangers, they raised more than a quarter of a million dollars in the first two months.

Crowdfunding, or raising money without pursuing donors individually, isn’t new; consider bake sales, telethons, or the Salvation Army drum. But the endeavor, like sharing photographs and shopping, has gained form and focus in an age of digital connection. On the Internet, crowdfunding is distinguished by its scale. As of 2017, GoFundMe alone had raised five billion dollars. That money has helped many of its users, and it has helped the company grow.

GoFundMe was officially founded, in 2010, by Andy Ballester and Brad Damphousse, who had met at a text-messaging startup. Since then, the company has hosted more than two million fund-raising campaigns in nineteen countries, joining other platforms, such as Indiegogo and Kickstarter. Unlike those, GoFundMe is associated with causes more than it is with projects, in part because it has a history of offering relief in disaster zones. On June 12, 2016, after a gunman opened fire at the Pulse night club, in Orlando, a GoFundMe campaign was started for victims and their families. A hundred and nineteen thousand people donated, raising almost eight million dollars. In late 2017, the Time’s Up Legal Defense Fund launched a campaign for victims of sexual assault, raising about twenty-five million dollars. All of this followed Taylor Swift’s use of the platform, in 2015, to send fifty thousand dollars to a blond girl with leukemia, an act that inspired GoFundMe to raise individual-donation maximums from fifteen thousand dollars to fifty thousand dollars.

Owing to such magic-seeming intercessions, GoFundMe has acquired a wishing-well mystique. The sorts of help that people seek, meanwhile, trace the profile of American need. A third of the money raised on GoFundMe in 2017 was for medical expenses. This isn’t surprising, given that the United States has the highest over-all health-care costs in the developed world. Since 2008, health-insurance deductibles have increased eight times as quickly as wages. A study in The American Journal of Medicine last fall found that 42.4 per cent of the 9.5 million people diagnosed with cancer between 2000 and 2012 had depleted their assets within two years. Like the vase between the faces in the famous optical illusion, GoFundMe has become a negative-space portrait of our country’s teetering medical finances, a repository for the costs that patients and underwriters cannot or will not cover on their own.