One Little Girl’s Story Highlights the Promise of Precision Medicine

Posted on October 23rd, 2019 by Dr. Francis Collins

Photo of Dr. Yu taking a selfie with Mila and her mom — Caption: Mila with researcher Timothy Yu and her mother Julia Vitarello. Mila’s head is covered in gauze because she’s undergoing EEG monitoring to determine if her seizures are responding to treatment. Credit: Boston Children’s Hospital

Starting about the age of 3, Mila Makovec’s parents noticed that their young daughter was having a little trouble with words and one of her feet started turning inward. Much more alarmingly, she then began to lose vision and have frequent seizures. Doctors in Colorado diagnosed Mila with a form of Batten disease, a group of rare, rapidly progressive neurological disorders that are often fatal in childhood or the teenage years. Further testing in Boston revealed that Mila’s disease was caused by a genetic mutation that appears to be unique to her.

No treatment existed for Mila’s condition. So, in an effort to meet that urgent need, Timothy Yu and his colleagues at Boston Children’s Hospital set forth on a bold and unprecedented course of action. In less than a year, they designed a drug that targeted Mila’s unique mutation, started testing the tailor-made drug for efficacy and safety on cells derived from her skin, and then began giving Mila the drug in her own personal clinical trial.

The experimental drug, which has produced no adverse side effects to date, hasn’t proved to be a cure for Mila’s disease. But it’s helped to reduce Mila’s seizures and also help her stand and walk with assistance, though she still has difficulty communicating. Still, the implications of this story extend far beyond one little girl: this work demonstrates the promise of precision medicine research for addressing the unique medical challenges faced by individuals with extremely rare diseases.

Mila’s form of Batten disease usually occurs when a child inherits a faulty copy of a gene called CLN7 from each parent. What surprised doctors is Mila seemed to have inherited just one bad copy of CLN7. Her mother reached out online in search of a lab willing to look deeper into her genome, and Yu’s lab answered the call.

Yu suspected Mila’s second mutation might lie buried in a noncoding portion of her DNA. The lab’s careful analysis determined that was indeed the case. The second mutation occurred in a stretch of the gene that normally doesn’t code for the CLN7 protein at all. Even more unusual, it consisted of a rogue snippet of DNA that had inserted itself into an intron (a spacer segment) of Mila’s CLN7 gene. As a result, her cells couldn’t properly process an RNA transcript that would produce the essential CLN7 protein.

What might have been the end of the story a few years ago was now just the beginning. In 2016, the Food and Drug Administration (FDA) approved a novel drug called nusinersen for a hereditary neurodegenerative disease called spinal muscular atrophy (SMA), caused by another faulty protein. As I’ve highlighted before, nusinersen isn’t a typical drug. It’s made up of a small, single-stranded snippet of synthetic RNA, also called an oligonucleotide. This drug is designed to bind to faulty RNA transcripts in just the right spot, “tricking” cells into producing a working version of the protein that’s missing in kids with SMA.

Yu’s team thought the same strategy might work to correct the error in Mila’s cells. They reasoned that an appropriately designed oligonucleotide could block the effect of the rogue snippet in her CLN7 gene, allowing her cells to restore production of working protein.

The team produced candidate oligonucleotides and tested them on Mila’s cells growing in a lab dish. They found three candidates that worked. The best, which they named milasen after Mila, was just 22-nucleotides long. They designed it to have some of the same structural attributes as nusinersen, given its established safety and efficacy in kids with SMA.

Further study suggested that milasen corrected abnormalities in Mila’s cells in a lab dish. The researchers then tested the drug in rats and found that it appeared to be safe.

A month later, with FDA approval, they delivered the drug to Mila, administered through a spinal tap (just like nusinersen). That’s because the blood-brain barrier would otherwise prevent the drug from reaching Mila’s brain. Beginning in January 2018, she received gradually escalating doses of milasen every two weeks for about three months. After that, she received a dose every two to three months to maintain the drug in her system.

When Mila received the first dose, her condition was rapidly deteriorating. But it has since stabilized. The number of seizures she suffers each day has declined from about 30 to 10 or less. Their duration has also declined from 1 or 2 minutes to just seconds.

Milasen remains an investigational drug. Because it was designed specifically for Mila’s unique mutation, it’s not a candidate for use in others with Batten disease. But the findings do show that it’s now possible to design, test, and deploy a novel therapeutic agent for an individual patient with an exceedingly rare condition on the basis of a thorough understanding of the underlying genetic cause. This is a sufficiently significant moment for the development of “n = 1 therapeutics” that senior leaders of the Food and Drug Administration (FDA) published an editorial to appear along with the clinical report [2].

Yu’s team suspects that a similar strategy might work in other cases of people with rare conditions. That tantalizing possibility raises many questions about how such individualized therapies should be developed, evaluated, and tested in the months and years ahead.

My own lab is engaged in testing a similar treatment strategy for kids with the very rare form of premature aging called Hutchinson-Gilford progeria, and we were heartened by this report. As we grapple with those challenges, we can all find hope and inspiration in Mila’s smile, her remarkable story, and what it portends for the future of precision medicine.

References:

[1] Patient-customized oligonucleotide therapy for a rare genetic disease. Kim J, Hu C, Moufawad El Achkar C, Black LE, Douville J, Larson A, Pendergast MK, Goldkind SF, Lee EA, Kuniholm A, Soucy A, Vaze J, Belur NR, Fredriksen K, Stojkovska I, Tsytsykova A, Armant M, DiDonato RL, Choi J, Cornelissen L, Pereira LM, Augustine EF, Genetti CA, Dies K, Barton B, Williams L, Goodlett BD, Riley BL, Pasternak A, Berry ER, Pflock KA, Chu S, Reed C, Tyndall K, Agrawal PB, Beggs AH, Grant PE, Urion DK, Snyder RO, Waisbren SE, Poduri A, Park PJ, Patterson A, Biffi A, Mazzulli JR, Bodamer O, Berde CB, Yu TW. N Engl J Med. 2019 Oct 9 [Epub ahead of print]

[2] Drug regulation in the era of individualized therapies. Woodcock J, Marks P. N Engl J Med. 2019 Oct 9 {Epub ahead of print]

Links:

Batten Disease Fact Sheet (National Institute of Neurological Disorders and Stroke/NIH)

Mila’s Miracle Foundation (Boulder, CO)

Timothy Yu (Boston Children’s Hospital, MA)

NIH Support: National Center for Advancing Translational Sciences