John Landers of the University of Massachusetts Medical School in Worcester said ALS attacks motor neurons, the nerve cells responsible for controlling muscles leading to paralysis and difficulty swallowing.
Landers and international researchers searched for gene mutations in two large families with an inherited form of ALS, using a technique to decode only the protein-encoding portions of DNA.
The deep sequencing of the exome led to the identification of several different mutations in the gene for profilin -- PFN1 -- which were present only in the family members that developed ALS.
After identifying the PFN1 mutations in ALS patients, the researchers demonstrated that the mutations inhibited axon, or nerve, growth in laboratory-grown motor neurons as well.
The study, published in the journal Nature, found mutant profilin accumulated in clumps in neural cells associated with ALS, Parkinson's and Alzheimer's.
"This discovery is highly significant and opens a new avenue of research," Amelie Gubitz, program director at the National Institute of Neurological Disorders and Stroke, which funded the research. "There is growing evidence that ALS may be caused by a variety of cellular defects, and that it is a not a disorder with a single origin. Whether and where these disease pathways converge is an active area of research with important implications for therapy development."