Duke University in Durham, N.C., and colleagues, examined the severity of muscle degeneration and conducted microscopic analysis of muscle fibers in mice bred to produce mutated myotilin alone or mutated myotilin and higher-than-average levels of normal myotilin.

They found the mice making mutant myotilin had signs of LGMD1A, but those making increased levels of normal myotilin in addition to the mutated protein had increased severity of symptoms. These included earlier onset and a greater involvement of muscles less affected in mice that produced only mutant myotilin.

The researchers indicated that a “knockdown” approach, in which the amounts of both abnormal and normal myotilin are reduced, might be an effective therapeutic strategy for LGMD1A, although Hauser suggests more work may be needed in developing highly efficient knockdown methods, and “it may turn out that

effective therapy will require a combination of several different methods at once.”

Calling the mouse experiment “a big step forward in understanding the mechanism in LGMD1A,” Hauser noted, “This improved understanding of mechanism is an important part of designing effective therapies for any muscular dystrophy.”

ID of protein that
prevents myelin formation
could have implications
for CMT treatment

Scientists in the United Kingdom and Italy have found that a protein called c-jun keeps cells associated with nerve fibers from maturing and producing myelin, a fatty sheath that insulates the fibers and speeds transmission of signals to and from nerve cells.

Kristjan Jessen at University College London and colleagues, who reported their findings May 19 in the Journal of Cell Biology, say it’s

likely the normal role of c-jun is to push myelin-making cells, known as Schwann cells, back to a more primitive state after nerves are injured. Schwann cells normally return to this earlier stage of development after injury, they note, as part of the process of nerve-fiber repair and regeneration.

However, in Charcot-Marie-Tooth disease (CMT), abnormal loss of myelination occurs, slowing nerve signals and leading to disability. Several forms of CMT, including the relatively common CMT1A and CMT1B, as well as other diseases, are characterized by abnormalities in myelination of nerve fibers.

The investigators say it will be important to determine whether c-jun is involved in causing these abnormalities. If so, they say, targeting c-jun might open new avenues for treatment. q

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