So how did I get involved in all this? For my part, I was a molecular biologist turned mercenary human geneticist. Prior to June 1991, I slaved away in the labs of the Dana-Farber Cancer Institute. As a postdoc in the laboratory of Dr. Lorraine Gudas, I worked hard but was unable to publish even a single paper in my four-year internship, a prescription of certain death for a young scientist’s career. Coldly evaluating my chances for attaining an assistant professor or corporate scientist position anywhere, I decided they were not good. Genuinely believing that I was likely on my way out of research biology, I decided that, as a swan song, I would donate what skills I possessed to an area that might benefit from them—hereditary human diseases.

I had interviewed with Dr. Robert H. Brown, Jr., a neurologist-scientist at MGH, and one of the principals of the Boston ALS genetics effort. The other was Dr. H. Robert Horvitz, the C. elegans developmental biologist at MIT, and a Hughes investigator. The ALS genetics effort was centered in Dr. Brown’s MGH lab. Already on-board were a dedicated technician, Peter Sapp, and an incomparable study coordinator, Nurse Diane McKenna-Yasek, who was liaison to the many family members participating in the research. Another technician, Jerry O’Regan, was later added to the group.

Dr. Brown was a charismatic individual with an obvious passion for solving the ALS riddle. In my interview, he provided an overview of the project, and a description of the planned work, going forward. During this meeting, I experienced a strong conviction that I could find this gene, given my background in molecular genetics from my graduate student days at Brandeis University, when, among other things, I performed a 100 Kb walk on the Drosophila X chromosome. I felt certain that I could be useful to Dr. Brown, if he would hire me. He eventually did, and I was given the nebulous title, "Project Leader." (I would be remiss if I did not mention that it was likely the recommendation of Dr. Michael Rosbash, a Brandeis professor and a Hughes investigator, to Dr. Horvitz that secured my role in this project).

It would take too much space to relate in detail the history of the research that led to the identification of SOD1 as the chromosome 21 ALS gene. The short version: the early ALS linkage effort culminated in a May, 1991 report in the New England Journal of Medicine, describing the results for a collection of 23 ALS families; these results suggested linkage to the long arm of human chromosome 21. But the highest combined two-point LOD score for the 23 families was only 2.89, less than the required score of 3.0 to firmly establish linkage. Linkage was formally established using a multipoint analysis of four chromosome 21 DNA markers. Still, the results were underwhelming for a cohort of 23 families, and the report was received by the human genetics community with deafening silence and, perhaps, skepticism. As a result, when I joined the team, I personally was decidedly uncertain that there really was an ALS gene on chromosome 21. It was not until I had isolated new microsatellite DNA markers from the linked region of chromosome 21 that the issue was settled. In a paper that was intended to be published before the Nature paper, we reanalyzed linkage of ALS to chromosome 21 using ten chromosome 21 microsatellite DNA markers (Rosen et al., "Genetic linkage analysis of familial amytrophic lateral sclerosis using human chromosome 21 microsatellite DNA markers," Am. J. Med. Genet. 51: 61-69, 1994). In this report, we describe a maximal two-point LOD score of 4.29 @ 5 cM from the DNA marker, D21S223 for a set of thirteen ALS families. LOD scores for other markers, especially D21S63, were supportively high. Linkage was confirmed; there really was an ALS gene on chromosome 21.

When the discovery finally did come, it came like a tsunami, sweeping us along in a chaos of alphabet soup: PCR, SSCP, and A, G, C, T (DNA sequencing). I had prepared a final version of the above manuscript and was in the process of submitting it. But then we began finding a plethora of mutations in the SOD1 gene, and everything was dropped in the frantic scurry to document as many different mutations associated with ALS as quickly as possible. The linkage paper, which should have preceded the Nature one, as it set the stage for the latter, was eventually published in the American Journal of Medical Genetics. In my humble opinion, it is a beautifully clean piece of work, a model for the presentation of linkage results, but it has been largely ignored, completely eclipsed by the SOD1 report in Nature.

Details surrounding the submission and publication of the Nature report are fascinating, and provide great insight into human nature. Thanks to the efforts of Dr. Horvitz, the manuscript was circulated and evaluated among three prominent scientists, and was accepted for publication by Nature within 72 hours, which may be a record for a Nature manuscript. There was a possibility (but one I doubt was taken seriously) that I would not have been first author; it was suggested by another scientist to Dr. Brown that "I’ll be first author, and you, Bob, can be last, as we usually do." This was followed by a telephone-mediated war by two parties for second author. I have heard a rumor that one scientist who had nothing to do with the research, successfully pleaded, on their knees and with tear-filled eyes, to be included as an author; s/he was.

Ultimately, 33 researchers made it onto the list of authors. Of these, I was either familiar with or have met 22 over the past decade; I still have not met 10 of my co-authors. The decision was made early on by Dr. Brown to commemorate the efforts of all serious ALS genetics researchers by including them as authors on this report, a view that I embrace as proper. Interestingly, the extensive list of authors almost cost me a job. While interviewing for a position with the Division of Genetic Disorders at the NY State Department of Health, one of the senior administrators expressed to me the opinion that I could not have contributed substantially to the discovery if so many people were involved.

Of course, many others who were not authors contributed to the research, directly and indirectly, and it would be impossible to mention them all. Locally, our group was heavily dependent on the methods and expertise of the bevy of scientists working with Jim Gusella, not to mention reagents (thank you, Kathy M., for all those oligos you made for us!) Externally, our efforts profited from direct collaborations with people like David Patterson and Michael Brownstein. And there were all of the "indirect" collaborators, whose previous results and materials facilitated our work. People like Sidney Pestka, whose lab made the 3x1s chromosome 21 cosmid library, and Paul Watkins, for cosmid PW517, from which I isolated the key microsatellite DNA marker, D21S63. And Irwin Fridovich and Yoram Groner for the seminal work on the Cu, Zn superoxide dismutase enzyme and the SOD1 gene, respectively. Could Ditsa Levanon ever have anticipated how important her 1985 EMBO paper on the architecture and sequence of the human SOD1 gene would be to us seven years later? I would like to take this opportunity to thank everyone who contributed to this research in any manner.

The immediate significance of this work is fairly obvious: mutations in the SOD1 gene were the first significant cause of ALS identified in the long history of research on the disease. SOD1 mutations cause approximately 20% of all hereditary ALS cases; they do not seem to cause many, if any, cases of sporadic ALS. We had hints that SOD1 would not be the causative gene for all hereditary ALS, as some ALS families we were studying did not have a high posterior probability of linkage to chromosome 21. But we were very disappointed that it was not a cause of sporadic ALS, which represents 90% of all ALS cases. The immediate implications of our findings were: 1) that there is at least one other ALS gene, and possibly, several; and 2) sporadic ALS has an etiology distinct from at least SOD1 hereditary ALS, and one that might be radically different in pathophysiology. But if SOD1 failed to be the complete answer to ALS, it was the first answer, and one that has given much hope for the eventual conquering of this disease. It gave other researchers a starting point from which to work.

Immediate developments that arose directly from this work include the construction, first by collaborator Mark Gurney and then others, of an animal model for ALS, in the form of mice harboring mutated SOD1 transgenes. These mice, which dramatically reproduce the features of human ALS, have been a huge source of information about the disease, permitting not only analysis of the etiology of ALS from the earliest stages right through to death, but also the screening of compounds that might mitigate or even prevent ALS. And there has been an enormous amount of work on SOD1 and Cu, Zn superoxide dismutase. But the latter has yielded very few secrets regarding ALS.

The SOD1 discovery demonstrated in an awesome way the incredible power of linkage analysis. Using only a small set of families, a proportion of which were not even linked to the same gene, each with a limited number of affected individuals, it was possible to find a gene causing an important disease. By the time the Nature paper appeared, we knew that SOD1 caused only about 20% of hereditary ALS cases, meaning that one or more unidentified genes caused the other 80% of cases. Finding these other genes should eventually provide insight into the cellular/molecular mechanism that causes ALS—not only in the hereditary, but perhaps also in the sporadic cases. It is not without some consternation that I must point out it is only recently that other ALS genes have been genetically mapped or identified. A more aggressive campaign of investment in ALS genetic research by various public and, especially, certain private funding agencies over the past decade could have expedited these discoveries, and substantially improved our current conception of the etiology of ALS.

In the past dozen years, I have learned much regarding human genetics research, and more generally, regarding how to successfully bring a research project to fruition. If there is any advice I can give to anyone, I would say, "ALWAYS use the right tool for the job." Knowing what is needed, of course is the tricky part, but not infrequently, it is the right person, one who has a combination of drive, attitude, and the proper skill set to get the job done. I was the right person for finding the chromosome 21 ALS gene. Sure, the gene would probably eventually have been found, but it would have required substantially longer than the year and a half that it took. The right tool, sometimes in the form of the right person, can mean the difference between a quick answer and, possibly, no answer at all.

The personal responses of various people regarding this paper have been widely varied. Perhaps the greatest compliment I have ever received from a colleague for any of my work as a scientist was the comment, "Nice piece of work," from Stylianos Antonarakis. At the other end of the spectrum, a response typical of that rendered by a Michigan mouse geneticist, and all too common, is "I heard you just got lucky." Maybe so. I have always tried to be humble and self-deprecating regarding the discovery, and have made it a point to credit Drs. Brown and Horvitz as the principals at every opportunity. I am continually surprised when people I have never met are impressed at meeting me, my reputation from this paper apparently preceding me. During the period following the discovery, I attempted to remain emotionally level, aware of the terribleness of the disease, of all the people affected by it, and of a job that was incomplete. But maybe I restrained my emotions overly: I now feel that perhaps I should have indulged more in the joy that comes with a significant discovery. But an opportunity lost is lost forever…

The discovery of an ALS gene was an incredible experience, and I know that I was fortunate to have been a part of the process. In many ways, it was the hardest thing, professionally, that I have ever done. Back then, in the midst of all of the excitement, Bob Brown told me that this would probably be the biggest paper of my career. The possibility had not occurred to me until he said it, and, in a fashion, I was offended to think this might be true, given that I was not yet even an Assistant Professor, with an opportunity to demonstrate my abilities as an independent investigator, and still with a substantial career ahead of me. But given recent occurrences in my career, it appears Bob might be right, after all.

Dedicated in affectionate friendship to Rick Boyce, the second person ever to see an ALS mutation. Cheers!

Daniel R. Rosen, Ph.D.
Wadsworth Center
New York State Department of Health
Albany, NY, USA
Copyright© 2003 Daniel R. Rosen; all rights reserved