Search for ALS Gene Narrows

Medically Reviewed by Jacqueline Brooks, MBBCH, MRCPsych
From the WebMD Archives

Oct. 3, 2000 (Atlanta) -- Scientists may be one important step closer to pinpointing a genetic glitch responsible for amyotrophic lateral sclerosis (ALS) -- the incapacitating neurodegenerative disease first brought into the public eye by beloved Yankees first baseman Lou Gehrig and more recently described in the best-selling biography Tuesdays with Morrie.

"In some people with this disease, we've identified a region of chromosome 9 that contains a gene that is probably causing their illness," says Betsy A. Hosler, PhD, research fellow at Massachusetts General Hospital and an instructor at Harvard Medical School in Boston. "We don't know yet what gene it is, but we've reduced the area in which we're looking from the whole genome to this particular section of this particular chromosome."

Hosler, lead author of an ALS study appearing in the Oct. 4 Journal of the American Medical Association, discussed her findings here today at the 19th Annual Science Reporters Conference.

Each ALS case is described as either sporadic -- the victim knows of no other instances in his or her family -- or as familial -- where the individual can identify another family member with the disease. "In 5% of all cases, individuals also develop symptoms of a particular type of dementia called frontotemporal dementia," Hosler says.

In earlier work, the team found a connection between a region of chromosome 9 and certain cases of familial ALS. When the team focused only on these cases, "it was very striking to us how the linkage is to families that also have dementia, but not those that don't have dementia," she says.

The hope, she says, "is that by studying this region further and identifying the particular gene causing [the problems], and then studying the biology of that gene," we can understand the disease process and why neurons are dying in these patients."

ALS usually strikes in early to middle adulthood, Hosler says. Beyond a certain age, it is unlikely that an unaffected individual will develop the disease. So to identify patterns of genetic mutation indicative of ALS, the team compared the chromosomes of affected individuals with those of both affected and older, unaffected relatives.

"When we see a pattern, and our analysis indicates that the probability is over 1 in 1,000 that it's not just chance, we have a marker," she says. "We then look at the nearby areas [of the chromosome]. When we see the same variations in affected people in 10 markers in a row, that gets our attention." Eventually, with luck, they've found the gene.

But as in all genetic research, Hosler tells WebMD, knowing where the problem lies is just the beginning. Whether or not the findings lead to an effective therapy will ultimately depend on the nature of the genes in question, and what, precisely, has gone wrong with them.

As a sad example, Hosler points to her team's earlier discovery of a link between certain ALS cases and a mutation in a well-researched gene called SOD.

"We thought we could dive right in and do something about it," she says. Because SOD produces a protein that protects cells from damaging free radicals, "we thought that the problems in ALS were due to a loss of that protection, and that we could simply supplement the missing protein product."

But that was not the case.

The mutant proteins were "working just fine at what they were supposed to do," she says. "The problem was that they were doing something in addition to what they were supposed to be doing." And eliminating something extra, she tells WebMD, is much harder than adding in something that's missing.

On average, says Hosler, ALS victims die within five years of their diagnosis. "But some survive up to 30 years," she says, "and there is no way to know how fast a particular patient will progress."

What's more, this kind of variation occurs within families, indicating that much more is at work than any one genetic glitch. Based on mouse studies, she tells WebMD, where different breeds develop symptoms at varying rates, "we're pretty sure that there are outside factors involved." Whether those forces are environmental, genetic, or more likely a combination of both, remains to be seen.

What is reassuring, Hosler says, is that any therapy generated by this research in familial ALS should be applicable across the board.

"Even if the absolute root cause of sporadic and familial ALS is different, the steps to the visible symptoms of disease have got to be similar and the therapy should help everyone"