In this Oct. 21, 2014, photo, Michael Jones encourages his son Landon, 12, to eat some of his food after school. Landon has lost 35 pounds due to an apparent hypothalamic dysfunction which started just over a year ago, causing him to lose all feelings of hunger or thirst. Mary Willie/The Des Moines Register

Most children would jump at the chance to pig out on hamburgers, ice cream, peanut butter and jelly sandwiches, tacos and candy. But not Landon Jones. For about a year, the 12-year-old Iowa boy has had a mysterious illness. He never feels hunger or thirst and therefore refuses to eat and drink. The disorder is so rare that doctors think he may be the only person in the world with the condition, according to the Des Moines Register, which first reported his story.

The strange symptoms developed without warning a year ago. Landon awoke the morning of Oct. 14, 2013 complaining of dizziness and extreme chest congestion. A scan of his chest indicated he had a bacterial infection in his left lung, which was treated successfully.

But then he stopped eating.

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Over the past year, Landon and his family have visited doctors in five cities, from their local pediatrician in Waterloo, Iowa, to the Mayo Clinic in Rochester, Minn. He's been subjected to countless tests, including a spinal tap, encephalograms (brain scans) and psychiatric evaluation, and has been evaluated for a host of medical conditions, including digestive problems and possible eating disorders.

One by one, other illnesses have been ruled out, but Landon still has not received a diagnosis. The physicians he's visited have been baffled by his condition and at a loss for how best to treat him.

Dr. Marc Patterson, a neurologist at the Mayo Clinic who first examined Landon last November, told the Des Moines Register that the boy's case may be the only one like it in the world.

In the meantime, his parents have no choice but to plead, bargain and cajole their son to eat and drink

Landon continues to lose weight -- more than 35 pounds so far, a third of his previous body weight. Before he developed the illness, he was a stocky 104 pounds, but he now weighs in at just 68.4 pounds. The illness has left him weak and forced him to give up many of his favorite activities, including playing the trombone because it made him dizzy. He's missed dozens of days of school.

Doctors may have to insert a gastronomy tube in order to provide him with nourishment directly into his stomach.

As they continue their medical detective work, doctors are looking into the possibility that Landon may suffer from a rare hypothalamic dysfunction. The hypothalamus is an area of the brain that's about the size of a pea and controls a number of functions, including hunger and thirst, blood pressure and sleep. It's also linked to the pituitary gland, which is partially responsible for the body's stress response. Some causes of hypothalamic dysfunction can include malnutrition, infection, genetic disorders, head injury and tumors.

One possible clue to his illness is the fact that three years ago, Landon began having absence seizures in which he'd drift off and stare into space but then quickly snap out of it. It's unclear if -- or how -- the seizures or the medication he takes to control them may be linked to his current health problem.

But doctors still haven't gotten to the root of Landon's health problem, which is why his family has contacted a division of the National Institutes of Health that helps evaluate and treat patients with rare diseases. The Undiagnosed Diseases Program at the NIH works with patients whose conditions are uncommon or seem to defy understanding. Only 50 to 100 patients are invited each year to the NIH to be evaluated by these specialists, after a referral from the patient's primary care physician, and Landon's family hopes he'll be one of them.

In the U.S., a disease is considered rare if it affects fewer than 200,000 people, but Landon appears to be one of a kind.

Landon's parents talk about his condition in this video from the Des Moines Register: