December 2, 2009

Another Reason Not to Light Up

Smoking is found to be a definitive risk factor for Lou Gehrig’s disease

“The better-designed studies consistently show that smoking increases the risk of developing ALS,” says Carmel Armon. Photo: iStock

While previous studies have indicated a probable connection between smoking and amyotrophic lateral sclerosis (ALS), or Lou Gehrig’s disease, a new study by a Tufts neurologist concludes that smoking is in fact an established risk factor, and may actually cause the disease.

Carmel Armon, a professor of neurology at Tufts School of Medicine, performed a rigorous analysis of studies examining the link between smoking and developing ALS, a fatal neurodegenerative disease affecting the motor nerves and the voluntary muscles. He published his findings in the November 17 issue of Neurology, the medical journal of the American Academy of Neurology.

“Application of evidence-based methods separates better-designed studies from studies with limitations that may not be relied on,” says Armon, who is also chief of neurology at Baystate Medical Center, a Tufts-affiliated hospital in Springfield, Mass. “The better-designed studies consistently show that smoking increases the risk of developing ALS, with some findings suggesting that smoking may be implicated directly in causing the disease.”

The findings provide a link between the environment and the occurrence of ALS, where none had been previously identified with this level of certainty, Armon says. Thus, avoiding smoking “may reduce the occurrence of ALS in the future, and . . . recognizing its role in the occurrence of ALS may help pinpoint the biological processes that initiate the disease.”

ALS kills half of those affected within three years of the onset of weakness, with less than 5 percent surviving more than 10 years. Some 90 to 95 percent of cases appear to occur at random (they are called “sporadic cases”), while 5 to 10 percent can be linked to an affected blood relative (“familial cases”). An altered gene, several of which have been identified, is implicated in causing familial ALS. Prior to Armon's study, no external factors have been implicated with this level of confidence as contributing to the occurrence of sporadic ALS.

Armon notes that focusing on biological processes at the onset of sporadic ALS may provide new avenues to treatment to stop its progression.

“This has been realized in some animal models of familial ALS, but not in humans,” says Armon. “The hope that these concepts may apply to sporadic disease and change its outlook in the future is supported by establishing the association of smoking with ALS occurrence.”

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