ALS, also known as Lou Gehrig’s Disease in the USA, is a progressive neurodegenerative disease that affects nerve cells in the brain and the spinal cord. There is currently no known cause of the disease.
The research was led by J Paul Taylor, Department of Developmental Neurobiology at St Jude Children’s Research Hospital in Memphis, USA, and colleagues. They received funding through The ALS Association’s TREAT ALS (Translational research advancing therapies) programme.
The researchers discovered that mutations in genes for certain RNA-binding proteins cause them to switch between alternate shapes and aggregate, and to promote the same conformational change and aggregation of the normal protein. This behaviour has been seen in other neurodegenerative diseases, collectively called prion diseases, including mad cow disease and Creutzfeldt-Jakob disease. In those diseases, this ability leads to spread of the disease throughout the nervous system.
“This discovery may lead us to think more broadly about how ALS progresses within the brain and to ask whether a similar spreading process is occurring,” said Lucie Bruijn, chief scientist for The ALS Association.
The researchers also found that mutations in proteins called heterogeneous ribonuclear proteins (hnRNPs) caused an inherited disease in a small number of families with symptoms of ALS, the frontotemporal dementia, the muscle disease inclusion body myopathy, and the bone disorder Paget’s disease of bone. This cluster of symptoms, according to the study, has recently been recognised as a unique disorder called multisystem proteinopathy. The mutations increased the tendency of the hnRNP proteins to clump together and to induce non-mutated forms of the protein to do so as well. hnRNP proteins normally link to another ALS-associated protein called TDP-43, and the two were found together in the aggregates.
“While these mutations are themselves a very rare cause of ALS, they may provide an important clue about how other forms of ALS spread over time,” Bruijn said. “Preventing protein aggregation may be a viable therapeutic approach for many forms of ALS.”