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A Connecticut family is being accused of ‘medical child abuse’ after disagreeing with doctors at Boston Children’s Hospital over medical treatment for their daughter. The dispute has sparked an intense state custody battle for the past year - and has drawn attention to a very rare and mysterious disease.

Fifteen-year-old Justina Pelletier had been undergoing treatment at Tufts Medical Center in Boston for mitochondrial disease – a condition that prevents the body’s cells from properly producing energy. However, after Justina’s health began to decline in February 2013, her parents took her to Boston Children’s Hospital (BCH) to see a gastroenterologist who had recently moved to BCH from Tufts.

At BCH, doctors disagreed with Justina’s diagnosis, arguing that the root of the girl’s problems were largely psychiatric – and that she did not have mitochondrial disease. Stating that Justina’s parents were resistant to giving her the mental health treatment she needed, the hospital charged the Pelletier’s with ‘medical child abuse’ and had Justina removed from their custody.

Mitochondrial disease is a mysterious condition –and even experts admit that it is difficult to diagnose and treat. Here are five things to know about this strange ailment:

1. Mitochondrial disease can affect almost any organ in the body
Mitochondria are located in every cell of a person’s body, and are responsible for making energy and performing other vital functions. When mitochondria aren’t working properly, they can disrupt function in almost any of the body’s organs, according to Dr. Melissa Wasserstein.

“It has very vague symptoms, but typically involves organs high in energy like the heart or skeletal muscle or brain,” Wasserstein, director of the program for inherited metabolic diseases at The Mount Sinai Hospital in New York City, told FoxNews.com. “But symptoms are very vague, very difficult to diagnose, and are difficult for physicians or patients to recognize.”

2. Symptoms can vary
Because mitochondrial disease can affect any of the body’s organs, the symptoms can wildly vary.

“Muscle weakness is a big one, something called cardiomyopathy which is a weakness of the heart muscle, gastrointestinal problems with vomiting, diarrhea, inability to digest food,” Wasserstein said. “They can have problems with the endocrine organs. They can have diabetes, and they can have problems in brain function.”

Wasserstein said that if a patient presents with problems in a variety of organs, or with multiple conditions that are usually unrelated, it may be a clue that mitochondrial disease is to blame.

“For me as a clinician, a red flag would be if there [is] more than one organ involved. If they come in with diabetes and muscle weakness – they don’t usually go together,” Wasserstein said. “Or a kid with developmental delay and cardiomyopathy, that might be suggestive too.”

3. The condition is difficult to diagnose
Mitochondrial disease, which can run in families, is often extremely difficult to diagnose – and often requires a muscle biopsy or extensive genetic testing to confirm.

“If I have a patient come in that I would suspect has mitochondrial disease, muscle weakness, etc.…the first step is a few blood tests you can do to see if there are suggestions [of the condition],” Wassterstein said. “But the two best tests include a muscle biopsy and genetic testing.”

The Boston Globe reported that Justina did not undergo a muscle biopsy – but Wasserstein, who has not treated Justina, said doctors may have had a good reason for skipping the test.

“If a child is quite sick, you may not want to subject them to anesthesia,” Wassterstein said.

4.  Treatment also varies widely
Currently, treatment options for people with mitochondrial disease are not strong.

“Treatment usually involves a bunch of vitamins and cofactors,” Wasserstein said. “So, high doses of vitamin coQ10, [and] high doses of riboflavin, which you can buy in the health food store. Super high doses might help the mitochondria work better.”

Patients also take medications targeting whichever organs are affected by the disease. For example, if an individual has diabetes as a result of mitochondrial disease, he or she will take medication to treat that condition.

“In general, when we start a patient with known mitochondrial disease on treatment, we tell the family at the beginning it might not work, that there’s no specific treatment,” Wasserstein said.

5. Prognosis is unknown
It’s unclear what the future may hold for patient’s diagnosed with mitochondrial disease.

“It completely depends on how severe the mitochondrial disease is,” Wasserstein said. “Some patients, it will get worse, and they might eventually die. Some patients can remain stable, and it will be okay. And some patients can, though rarely, get better without [any treatment].”

For many patients, the prognosis depends entirely on which organs are affected by the disease.

“For instance if somebody has their heart involved, the prognosis will be a lot worse than if it’s just the skeletal muscle,” Wasserstein said. “It can be very variable, and some people can stabilize quite well, but it depends on each individual.”