In this Dec. 10, 2017 photo provided by the family, Jon and Kari Kilquist sit with their children, from left, Will, Emmy and Owen at their home in Murphysboro, Ill. Will was born with a long list of mysterious symptoms that require a wheelchair, feeding tube and other care but his doctors were stumped at the cause. A new national network that tackles the rarest of rare diseases finally gave his family a diagnosis, finding he was the only known patient in the world _ so far _ to harbor a particular gene mutation that caused his health problems. (Kilquist Family via AP)

In this Dec. 10, 2017 photo provided by the family, Jon and Kari Kilquist sit with their children, from left, Will, Emmy and Owen at their home in Murphysboro, Ill. Will was born with a long list of mysterious symptoms that require a wheelchair, feeding tube and other care but his doctors were stumped at the cause. A new national network that tackles the rarest of rare diseases finally gave his family a diagnosis, finding he was the only known patient in the world _ so far _ to harbor a particular gene mutation that caused his health problems. (Kilquist Family via AP)

WASHINGTON (AP) — The youngster’s mysterious symptoms stumped every expert his parents consulted: No diagnosis explained why he couldn’t sit up on his own, or why he’d frequently choke, or his neurologic and intestinal abnormalities.

Then they turned to a new national network that aims to diagnose the rarest of rare diseases — and learned Will Kilquist is the only person known in the world, so far, to harbor one particular genetic mutation that triggered all those health problems.

“It kind of put me at peace with myself, knowing there is absolutely nothing I could have done to prevent this,” said Kari Kilquist of Murphysboro, Illinois, Will’s mother.

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The Undiagnosed Diseases Network , set up by the National Institutes of Health, turns scientists into detectives to attack medicine’s cold cases — the patients left in diagnostic limbo because their symptoms didn’t match any known diseases. The idea: Offer them access to cutting-edge research, at no cost, in hopes that uncovering unique ailments would improve overall medical knowledge.

Wednesday, the network published a snapshot of its early findings that highlight the desperate demand for help.

More than 1,500 people applied for an evaluation between 2015 and 2017 at the network’s initial seven patient sites. Just 601 in that first group were accepted, those deemed most likely to benefit, researchers reported in the New England Journal of Medicine.

Scientists came up with a diagnosis for about a third, 132 of the first 382 patients to complete their evaluations. And 31 of those diagnoses were never-before-known syndromes, according to the report.

Scientists hope to improve that diagnosis rate as more patients enter the program. Already, the application number has nearly doubled and more mysteries have been solved. Last month, the NIH added five more hospitals to the network.

Even those who didn’t get a diagnosis at first “say we have hope just knowing there are people looking at our case still and we’re not forgotten,” said Dr. Euan Ashley of Stanford University, one of the network sites.

Diagnosis doesn’t mean doctors automatically know how to help. One in 5 had a specific therapy recommended. Ashley said other families were able to cancel expensive follow-up testing; he calculated the network approach could cut tens of thousands of dollars from the typical patient’s diagnostic odyssey.

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In Illinois, Kari Kilquist didn’t expect Will’s treatment to change. He needs a wheelchair and feeding tube. He’s a happy child, about to turn 7, who spends his days in therapy and watching Sesame Street. Still his mother jumped at one last chance for diagnosis, and perhaps a way to learn what to expect as Will grows.

Will was examined at the NIH Clinical Center — the Bethesda, Maryland, hospital that first tackled undiagnosed diseases and expanded the research into a network. Doctors found problems others had missed: Will produces no saliva, the reason his airways frequently clog, and doesn’t sweat. The clues pointed to a gene defect that affects how the body transports crucial nutrients across cells, explaining Will’s developmental problems.

Now Kilquist wonders if, “Maybe Will could someday help another family learn more about their child.”

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The Associated Press Health & Science Department receives support from the Howard Hughes Medical Institute’s Department of Science Education. The AP is solely responsible for all content.