A study led by St. Jude Children's Research Hospital has discovered mutations in two genes that lead to the death of nerve cells in amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, and related degenerative diseases.
The same mutation occurred in both genes and led to the abnormal build-up of the proteins inside cells. These proteins play an essential role in normal RNA functioning and have also been linked to cancer, including the Ewing sarcoma, the second most common type of bone cancer in children and adolescents. The finding is the latest in a series of discoveries suggesting degenerative diseases and cancer may have common origins. RNA is the molecule that directs protein assembly based on instructions carried in DNA.
The study also adds to evidence that seemingly unrelated neurodegenerative diseases may involve similar defects in RNA metabolism. Researchers linked the problems to a specific region of the mutated proteins whose normal function was unclear. The study was published today in the advanced online edition of the scientific journal Nature.
"I hope this study helps to build the foundation for desperately needed treatments for ALS and perhaps a broad range of diseases caused by abnormal RNA metabolism," said J. Paul Taylor, M.D., Ph.D., an associate member of the St. Jude Department of Developmental Neurobiology and senior author of the study. Taylor and James Shorter, Ph.D., an assistant professor in the biochemistry and biophysics department at the University of Pennsylvania's Perelman School of Medicine, are the study's corresponding authors.
Each year approximately 5,600 people in the U.S. are found to have ALS. The disease is nearly always fatal, often within five years. Patients suffer muscle wasting and paralysis that affects their limbs and trunk as well as their ability to talk, swallow and breathe. There is no cure.
For this project, St. Jude sequenced just the portion of the genome called the exome, which carries instructions for making proteins. Researchers sequenced the exomes of two families affected by rare inherited degenerative disorders that target cells in the muscle, bone and brain. Neither family carried mutations previously tied to ALS or related diseases. The project built on the infrastructure developed by the St. Jude Children's Research Hospital -- Washington University Pediatric Cancer Genome Project, which played an important role in finding the mutations.
Researchers found the families carried a single, previously unknown mutation in a pair of RNA-binding proteins named hnRNPA2B1 and hnRNPA1. The proteins both bind RNA and help regulate its function. When researchers checked for the same mutations in 517 ALS patients they found hnRNPA1 protein mutated in two patients. One patient had the inherited form of ALS. The other ALS patient had no family history of the disease.