Charlie Gard: What to know about his rare condition

Sarah Toy

USA TODAY

The case of Charlie Gard, a terminally ill baby in the U.K. at the center of a life-and-death debate, has placed a spotlight on a little-known genetic disease called mitochondrial DNA depletion syndrome.

His case, which has pitted his parents against his providers and the British High Court, has caught the attention of both the pope and President Trump.

The controversy continues this week as the court weighs whether or not to allow the child’s parents to pursue experimental treatment for the rare, often-fatal disease in the United States.

Up until now, both British and European courts have sided with Charlie's hospital in deciding that his life support should end, saying that therapy will not help him and will cause further suffering. In Britain, if there is a dispute between parents and physicians over how to treat a patient, the courts have the final say about how to move forward.

Things changed last Friday when the hospital released a statement, saying: "Two international hospitals and their researchers have communicated to us as late as the last 24 hours that they have fresh evidence about their proposed treatment."

They added: "And we believe, in common with Charlie's parents, it is right to explore this evidence."

Here's what you should know about the medical facts of Charlie’s disease:

Charlie Gard: Parents to give new evidence on terminally ill British baby

Saving Charlie Gard: Fight for terminally ill British child goes on

What is the cause?

Charlie has mitochondrial DNA depletion syndrome, a type caused by a mutation in a gene called RRM2B. The gene helps code for an enzyme called ribonucleoside reductase, which helps make the building blocks for the DNA that ends up in the energy-producing centers of our body’s cells called the mitochondria.

Mutations in the RRM2B gene reduce the activity or amount of the ribonucleoside reductase enzyme, which leads to a shortage of DNA in mitochondria. This, in turn, leads to problems with mitochondrial function.

What are the symptoms?

RRM2B mitochondrial DNA depletion syndrome affects multiple organ systems. Babies with this disease have brain dysfunction, abnormally small heads and weak muscle tone, which lead to serious breathing problems. Charlie is deaf and cannot breathe without a ventilator.

These babies do not grow or gain weight the way they should and can have intestinal problems where the muscles and nerves of the digestive system don’t move food through properly. This can lead to swallowing issues, vomiting and diarrhea. They often have kidney problems as well.

As a result, these children usually only live to early childhood.

How do you get this?

The mutated gene is passed down from the parents.

It’s inherited in what is called an autosomal recessive pattern: In order for the disease to manifest, you have to inherit two copies of the mutated gene — one from your mom and one from your dad. If you only inherit one copy, you are a so-called “carrier,” but you won’t show any signs or symptoms of the disease.

Both of Charlie’s parents are carriers and they each passed a mutated gene to him. He ended up with two.

How common is this?

It is extremely rare; only 15 cases have been reported in the medical literature, according to one count.

Is there a cure?

Charlie's parents believe that a "nucleoside therapy" developed by a U.S.-based neurologist, identified in legal documents as Dr. I, may help their son. It has shown success in reducing the symptoms of some forms of mitochondrial disease in laboratory mice. It has also been tested in a small number of children, who have shown some improvement.

However, neither the mice nor the children have the same mutation as Charlie. It has never been tried on someone with his form of MDDS, and the doctor himself has said in the past that the child would be unlikely to improve with the experimental therapy.

What are the ethical considerations?

The case of Charlie Gard centers around the right of parents to choose what they believe is best for their children and the responsibility of authorities to ensure that those who are unable to speak for themselves receive appropriate care.

“The rationale for denying the parents experimental treatment is that he wouldn’t have a sufficient quality of life in (the court’s) judgment,” said G. Kevin Donovan, the director of the Edmund D. Pellegrino Center for Clinical Bioethics at Georgetown University Medical Center.

Donovan notes that things are done differently in the U.K. than in the U.S.

“In the United States, we look to the parents to make decisions for the child unless they are clearly (unable) to do so,” he said.

In the U.K, the approach is more paternalistic, he said. “When it comes to gray areas, where there is no obvious right or wrong, (the legal system) will feel free to overrule the parents’ decisions.”

Follow Sarah Toy on Twitter: @sarahtoy17