Scientist Says Clinical Trials Should Test Findings

Scientists have found evidence suggesting that the severity of spinal muscular atrophy (SMA) may be ameliorated by common vitamins.

The findings by researchers at the University of Pennsylvania School of Medicine, which are to be published Thursday in the journal Molecular Cell, suggest that folic acid and Vitamins B12 may limit the severity of symptoms that afflict SMA patients.

"We are not suggesting that this is a cure. But it may help," said Gideon Dreyfuss, PhD, Isaac Norris Professor of Biochemistry and a Howard Hughes Medical Institute Investigator at Penn, and principal author of the study.

SMA afflicts one of every 6,000-to-10,000 people and is the leading genetic killer of children under the age of two. But its symptoms-muscle weakness and wasting-differ in severity from person to person across a range of debilitation that scientists still cannot explain fully.

Most SMA patients die in their infancy, but some SMA patients do not become wheel-chair bound before the age of 20, and still others can live relatively normally until late in life. Until now, this variability has been attributed to "genetic modifiers" but the present study raises the possibility that it is influenced, perhaps to a significant extent, by nutritional factors.

Individuals afflicted with SMA have a genetic deficiency in a protein called SMN (survival of motor neurons), which is a "housekeeping" protein required by all cells -- especially motor neurons, the nerve cells that control the activity of muscles. When the levels of the SMN protein are too low, motor neurons are the first cells to degenerate, in turn leaving the major muscle groups without the stimulation they need to be viable.

To perform its function, SMN interacts with numerous proteins in the cell, helping them create some of the critical molecular machines that make messenger RNA and myriad proteins. In their research, Dreyfuss and his Penn colleagues, Westley J.Friesen, PhD, Severine Massenet, PhD, Sergey Paushkin, PhD, and Anastasia Wyce, PhD, have been studying what makes SMN interact with its partners in the cell.

The scientists made the surprising observation that SMN will bind efficiently -- and carry out its functions -- if the proteins to which it needs to bind are first "tagged" by specific enzymes. The tags are made up of methyl groups that are attached through the amino acid arginine to specific sites on SMN's protein targets (the process is 'methylation'), where they sit like "bumps" or "buttons" on the proteins' surface.

In addition to unraveling the function of the methylation of arginines in proteins -- a common modification process that was first reported more than 30 years ago whose function remained unknown until now -- the findings may have important implications for neurodegenerative disease.

The methyl group tags are supplied by a "methyl donor" called SAM (for S-adensylmethionine), and SAM receives this methyl group from folic acid (also known as folate) through a pathway that requires vitamin B12.

This, the Penn researchers believe, raises the possibility that deficiency in folate (many vegetables, grains and fruits are especially rich in folate) or the B vitamins could be particularly detrimental to SMA patients -- because it could result in under-methylated proteins, which are exactly the kind of proteins SMN needs to find to function properly.

Since SMA patients are already compromised in their levels of SMN, they might be expected to be more severely afflicted by such nutritional deficiencies.

"We would like to say, very cautiously, that our work raises the possibility that folic acid, and vitamin B12 may be helpful in lessening, even if only slightly, the severity of the disease for some SMA patients-or at least ensure that their condition is not worse than their genetics dictate," Dreyfuss said.

He cautioned against putting forth folic acid and the B vitamins as a "cure" for the disease, noting that his team's findings are based on laboratory biochemical studies which point the way to animal and/or human studies that need to be done before any clinical or therapeutic implications are drawn. "Certainly, we hope clinical studies will be initiated to see whether folate and the B vitamins make a difference for SMA patients that extends beyond laboratory research," he said.

The research was funded by a grant from the National Institutes of Health and by the Howard Hughes Medical Institute.


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