Stories about: neuromuscular disorders

Rallying a backup gene could boost strength in spinal muscular atrophy

Vivienne-20150819

Ed note: As of November 2016, Vivienne remains stable. On December 23, 2016, her test drug, to be marketed as SPINRAZA (TM), was approved by the Food and Drug Administration for all forms of SMA.

Spinal muscular atrophy (SMA), a condition affecting one in every 6,000 to 10,000 children, is caused by a defect in a gene called SMN1 — which stands for “survival of motor neuron.” The defect leaves children with too little functioning SMN protein to maintain their motor neurons, which begin wasting away. Muscle strength declines and children eventually develop difficulties eating and breathing.

For Vivienne, whose name means “to live,” that meant being slow to reach motor milestones like crawling, cruising and walking as a toddler. For her parents, it meant hearing that her life expectancy would not be normal.

But a new back-door approach seems to be helping Vivienne, now in first grade, at least thus far.

As it happens, most of us carry a backup gene for SMN1 — namely SMN2.

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Duchenne muscular dystrophy: The decade of therapy

A cocktail of approaches is most likely to successfully preserve muscle.
A cocktail of approaches is most likely to successfully preserve muscle.

It’s been 28 years since a missing dystrophin protein was found to be the cause of Duchenne muscular dystrophy (DMD), a disease affecting mostly boys in which muscle progressively deteriorates. Dystrophin helps maintain the structure of muscle cells; without it, muscles weaken and suffer progressive damage, forcing boys into wheelchairs and onto respirators.

Today, a variety of approaches that attempt to either restore dystrophin or compensate for its loss are in the therapeutic pipeline.

“We’re at the point where lots of things are going into clinical trials,” says Louis Kunkel, PhD, who is credited with identifying dystrophin in 1987. “I call it the decade of therapy.”

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Gene therapy strengthens weak muscles in congenital myopathy

Alison Frase with Nibs, a carrier of MTM whose descendants provided the basis for the gene therapy study.
Alison Frase with Nibs, a carrier of MTM whose descendants provided the basis for the gene therapy study.

Babies born with X-linked myotubular myopathy (MTM), which affects about one in 50,000 male births, are commonly referred to as “floppy.” They have very weak skeletal muscles, making it difficult to walk or breathe; survival requires intensive support, often including tube feeding and mechanical ventilation. Most children with MTM never reach adulthood.

One of these children, Joshua Frase, succumbed to MTM on Christmas Eve, 2010. The son of former NFL player Paul Frase, he lived to age 15. But his parents, who continue to actively support MTM research, now see a glimmer of hope for children born with the disease today.

A preclinical study on the cover of last week’s Science Translational Medicine, funded in part by the Joshua Frase Foundation, showed dramatic improvements in muscle strength using gene replacement therapy in mouse and dog models of MTM—paving the way for a potential clinical trial.

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Restoring muscle function in a rare, devastating disease: Part 1

Will Ward at the NSTAR Walk for Boston Children’s Hospital in 2012.

This two-part series examines two potential treatment approaches for myotubular myopathy, a genetic disorder that causes muscle weakness from birth.

Sixth-grader William Ward cruises the hallways at school with a thumb-driven power chair and participates in class with the help of a DynaVox speech device. Although born with a rare, muscle-weakening disease called X-linked myotubular myopathy, or MTM, leaving him virtually immobile, he hasn’t given up.

Neither has Alan Beggs, PhD, who directs the Manton Center for Orphan Disease Research at Boston Children’s Hospital, and who has known Will since he was a newborn in intensive care.

“From the very beginning, Alan connected with our family in a very human way,” says Will’s mother, Erin Ward. “In the scientific community, he’s been the bridge and the connector of researchers around the world. That makes him unique.”

Since the 1990s, Beggs has enrolled more than 500 patients with congenital myopathies from all over the world in genetic studies, seeking causes and potential treatments for congenital myopathies—rare, often fatal diseases that weaken children’s skeletal muscles from birth, often requiring them to breathe on a ventilator and to receive food through a gastrostomy tube.

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Spinal muscular atrophy: Helping nerve fibers find their way

Replacing the missing SMN protein seems to strengthen muscles in mice -- but not in human trials. Now, a closer look at SMN's function offers up new leads for drug discovery.

Spinal muscular atrophy is sometimes referred to as a “Lou Gehrig’s disease of babies.” About 1 in 40 people carry the defective gene for this untreatable recessive disease, which causes progressive muscle degeneration and is the leading genetic killer of infants and toddlers. Affected children have weak, floppy legs and arms and must go on ventilators, too weak to breathe on their own.

Researchers have had some success in mouse models of spinal muscular atrophy by adding back SMN, the protein that’s missing or abnormal, or getting the mice to produce more of it. The mice live longer, and do seem to have stronger muscles. But not so in human clinical trials to date.

Looking for another approach, Mustafa Sahin and Judith Steen in Children’s F.M. Kirby Neurobiology Center asked a simple question: What does SMN do?

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