“It hurts, Mommy. It hurts so bad.�?

“I know, sweetie. I know.�?The mother knelt carefully next to the bed, making sure she didn’t jostle the mattress. Experience had taught her that any movement made a terrible pain even worse. As she stroked her daughter’s mass of curls, she could feel the warmth of her skin and knew she had a fever. In a few minutes, she would get the child some Tylenol and a hot towel to hold against her rioting stomach. She wasn’t sure if these rituals helped, but they gave her something to do to combat the helpless despair of watching her baby suffer this way over and over again.

Her daughter could always tell when an attack was brewing. After supper that evening, she sought out her mother. “It’s coming,�?she whispered as she wedged herself into her mother’s lap, her face pale, her lips almost white. She put her daughter to bed, and she and her husband waited. Maybe this time it would be different. But it wasn’t.

These mysterious episodes of fever and stomach pain had started two years earlier. It was their older son’s ninth birthday party, and their daughter had just started first grade. That first attack the mother attributed to excitement or anxiety or maybe something she had picked up at school. Her daughter had been well enough to eat some birthday cake, and she thought nothing of it until the same thing happened three weeks later. For the next year, every three or four weeks her little girl would get a fever and these strange and terrible stomachaches. She wouldn’t eat. She would barely drink.

The pain was usually on the right side. The child variously described it as sharp or crampy or achy. Sometimes she felt nauseated. She would lie curled on her side, her breath the only visible movement. After an hour, sometimes two or three, the pain would seem to ease up, and she’d slide into sleep. In a day or two, she would be back to normal �?until the next attack.

2. Investigation

Her pediatrician was baffled and sent the child to a gastroenterologist. When he wasn’t able to figure it out, her mother found Dr. Joseph Levy, the head of pediatric gastroenterology at New York University School of Medicine. He looked into her stomach and intestines with an endoscope in search of the cause of the painful episodes. Was it celiac disease? Ulcers? Crohn’s? The studies said no.

The only abnormal test result was an elevated sedimentation rate. This test measures inflammation based on how quickly red cells sink to the bottom of a test tube. The test suggested inflammation but couldn’t reveal where or why. Levy tested the patient for lupus, the most common chronic inflammatory disease among girls this age. The test was normal. Levy called the girl his little mystery and continued to search for an answer.

Her mother conducted her own investigation. She trolled the Internet and described her daughter’s symptoms to every doctor she knew. At one point, she outlined the symptoms to her own internist, and that finally provided some hope. After hearing about the regular bouts of fever and pain, he said right away, “Sounds like familial Mediterranean fever.�?He had never seen the disease but recognized the pattern from medical school. The mother quickly called Levy.

The specialist knew the disease well, he told her. It’s a genetic disorder usually seen in ethnic groups from the Mediterranean region. He had trained in Israel, where the disease was common, and her daughter’s symptoms didn’t fit the disease he knew. These children, he told her, have high fevers and an abdomen that’s rigid with pain. The disease is often mistaken for appendicitis, and many children end up in an operating room before their doctors figure out the diagnosis. He had examined her during an episode, and while he wasn’t sure what she had, he was pretty sure it wasn’t F.M.F. The mother could feel tears prickling her eyes. There had to be an answer somewhere.

That winter, the patient continued to have attacks of abdominal pain every few weeks. Then she developed pain in her right ankle. A second test for lupus was now abnormal. Based on this, Levy referred the girl to yet one more doctor: this time, a pediatric rheumatologist, Dr. Lisa Imundo.

In her office, parents and daughter retold their story once more as Imundo took notes. She asked about any other joint pains. Sure, there had been other aches and pains �?mostly in the knees �?but for the past few weeks the pain had moved to the ankle. The mother hadn’t mentioned it to Dr. Levy because her daughter played sports, and she had assumed the pains were due to little injuries. Any tick exposures? Imundo continued. Yes, they had a house in an area known to have deer ticks.

On exam, Imundo noted that the patient was a little overweight and more than a little anxious. Her abdomen was soft, her bowel sounds normal and she had no stomach tenderness. Her ankle was sore and had a limited range of motion but wasn’t red or swollen. Finally, Imundo laid out her plan. Since the second test suggested she might have lupus, she would send off blood to see if there was any other evidence that she had this puzzling autoimmune disease. It wasn’t a classic presentation, but the symptoms of lupus were protean. Lyme disease was also possible, though less likely. The stomach pains weren’t typical, but the wandering joint pain was.

“What about familial Mediterranean fever?�?the mother asked about her internist’s suggestion. It’s true that the disease was characterized by abdominal pain, Imundo reasoned. And patients with this disease were completely normal between episodes of fever and pain. But the abnormal blood work, taken when this child was healthy, would be unusual. However, a test had recently been developed for this unusual genetic disorder, she told them, and they could check.

3. Resolution

A week after the blood was drawn, Levy called the mother. “I was wrong,�?he told her straightaway. “Your daughter has familial Mediterranean fever.�?She and her husband each had one copy of the F.M.F. mutation, he explained. Carriers, with only one copy, have no symptoms but can pass it on to their children. With two copies, the body cannot make a protein essential to modulating the immune system. Without it, the army of white cells that normally protect the body can overreact, resulting in inflammation, pain and fever. The abdomen and joints are the most common sites of these attacks, but the lungs and heart can also be affected. Colchicine, a drug that inhibits some forms of inflammation, can prevent most attacks.

They started their daughter on colchicine the next day, and the attacks stopped as abruptly as they had started. The nightmare was finally over. That was seven years ago. As long as her daughter takes her medicine, the mother told me recently, the fever and pain are kept at bay.

I asked Levy why he had been so certain that the child didn’t have F.M.F. Until recently, he explained, F.M.F. had been a clinical diagnosis �?one made based on the patient’s symptoms and the physical exam. The identification of the gene and the subsequent development of the test �?which had only just become available at the time of this patient’s diagnosis �?changed doctors�?understanding of the disease, Levy told me. In medicine, we can only really know a disease once we have a test that can reliably identify it. “What we learned from the test was that there was a whole spectrum of disease,�?Levy said. “Before, we were only able to pick up what we now know were the most extreme forms of the disease �?the tip of the iceberg. Now we can find all the rest.�?