Toddler with 'childhood Alzheimer's' symptoms gets experimental treatment Marian McGlockin was diagnosed with the disease last fall.

 -- When Marian McGlocklin was born, she weighed just over 5 pounds. Her parents thought she looked extra-delicate.

"She was having trouble gaining weight," Marian's mother, Sara McGlocklin, told ABC News. "We'd say, 'She's so small, and she's not very strong.'"

Initially, doctors tried to reassure them that Marian was normal, according to McGlocklin. But eventually, as Marian failed to meet development milestones, they suspected something was wrong.

Last fall, doctors found that Marian's spleen was enlarged — a sign of Niemann–Pick disease, type C, a serious degenerative disorder.

The disease is caused by an inherited gene mutation, which does not allow the body to properly break down cholesterol and other fats (lipids), according to the U.S. National Library of Medicine. The cholesterol and other lipids start to accumulate to the point that they become toxic in the spleen, liver and brain. Eventually, this kills cells and causes symptoms like intellectual decline, learning difficulties, seizures, tremors, clumsiness and unsteady gait.

"What we think of as her being delicate is her low muscle tone," McGlocklin said.

It is also known as "childhood Alzheimer's" because of its degenerative effects on the brain. "I think the disease is even more shocking," McGlocklin said. "It's a loss of every single skill you have."

Many children diagnosed with the condition at a young age do not survive to adulthood, according to the NLM.

Hearing the diagnosis was a blow for the McGlocklins.

"It was so devastating," Sara McGlocklin told ABC News. "It was like the same feeling as when I found out my mom had cancer."

Marian, now 19 month old, was diagnosed at Children's Hospital of Los Angeles, and her doctors quickly looked for experimental treatments that could suppress the buildup of lipids.

Eventually, after speaking with other families who have children with the disease, they found Dr. Elizabeth Berry-Kravis in Chicago, who is treating children with the disease with VTS-270, a medication for which the FDA granted a limited approval — rare pediatric disease designation.

While the drug is not approved by the FDA for broader treatments, Marian was a candidate to receive the investigational drug as part of the FDA's compassionate-use program. This allows people with severe or fatal illnesses with no approved treatment to use drugs in development, in certain circumstances.

Marian traveled to Chicago last week for her first treatment, accompanied by her parents and her 4-year-old sister, Emily. The drug is injected directly into Marian's spinal cord in the hopes that it will reach her brain to counteract the effects of the disease.

"It's like getting an epidural or a spinal tap," Sara McGlocklin explained. "They have a needle in her spine, and they inject the medicine directly into her spinal fluid ... The theory is that the most possible will cross the blood-brain barrier and gets into the brain."

While the family is hopeful, McGlocklin said that it has been difficult to acknowledge that Marian will undergo this invasive treatment every two weeks for the foreseeable future.

"I asked the doctor, 'How long is it going to take?'" McGlocklin recalled. "The doctor said, 'We don't know for Marian. She is the youngest person to receive the drug.'"

Berry-Kravis, who is treating Marian at Rush University Medical Center and is a co-principal investigator of a VTS-270 study, said the drug was discovered during tests on mice with Niemann–Pick disease, type C. VTS-270 was not initially the drug being tested; it was used as a way to dissolve the original test drug so it could be injected into the mice. However, researchers discovered that both the control mice and the sick mice were improving and surmised that VTS-270 was the reason. It then became the test drug and went on to win FDA approvals as an orphan drug — a designation that allows for government incentives to develop treatments for rare diseases — and a rare pediatric disorder drug.

Berry-Kravis added that starting Marian early on the drug could be helpful because treating patients before they develop advanced symptoms can make a big difference.

"The idea of treating before symptoms is attractive from a neurological standpoint because once brain cells die, you can't get them back," she said. While still preliminary, she said, early results from ongoing trials were promising.

The McGlocklins are now back in their home in Monrovia, California, and will return to Chicago soon for more treatment. They hope to raise awareness about the disease by sharing Marian's story as she undergoes treatment. They are also raising funds for their travel and for further research into the disease.

"To receive the news that Marian had [Niemann–Pick disease, type C] and then learn not only is there a promising treatment but she could get it within a few weeks ... it felt like a door was opening to save her life before she even got one dose of the treatment," Sara McGlocklin said. "It was a massive wave of relief and felt like a huge turning point of hope for Marian's future."