This also leads to decreased levels of RNA-binding protein in the nucleus, which may mean that their target RNA transcripts do not undergo the normal processing. Other RNA metabolism genes associated with ALS include ANG, SETX, and MATR3.C9orf72 is the most commonly mutated gene in ALS and causes motor neuron death through a number of mechanisms. The pathogenic mutation is a hexanucleotide repeat expansion (a series of six nucleotides repeated over and over); people with up to 30 repeats are considered normal, while people with hundreds or thousands of repeats can have familial ALS, frontotemporal dementia, or sometimes sporadic ALS. The three mechanisms of disease associated with these C9orf72 repeats are deposition of RNA transcripts in the nucleus, translation of the RNA into toxic dipeptide repeat proteins in the cytoplasm, and decreased levels of the normal C9orf72 protein. Mitochondrial bioenergetic dysfunction leading to dysfunctional motor neuron axonal homeostasis (reduced axonal length and fast axonal transport of mitochondrial cargo) has been shown to occur in C9orf72-ALS using human induced pluripotent stem cell (iPSC) technologies coupled with CRISPR/Cas9 gene-editing, and human post-mortem spinal cord tissue examination.Excitotoxicity, or nerve cell death caused by high levels of intracellular calcium due to excessive stimulation by the excitatory neurotransmitter glutamate, is a mechanism thought to be common to all forms of ALS. Motor neurons are more sensitive to excitotoxicity than other types of neurons because they have a lower calcium-buffering capacity and a type of glutamate receptor (the AMPA receptor) that is more permeable to calcium.
In most preclinical studies the SOD1 mice were given the drug during the presymptomatic stage, which makes the results less likely to apply to people with ALS, who begin treatment well after their symptoms begin. Positive results in small phase II studies in humans could also be misleading and lead to failure in phase III trials. Other potential issues included the drug not reaching its intended site of action in the central nervous system and drug interactions between the study drug and riluzole.Repetitive transcranial magnetic stimulation had been studied in ALS in small and poorly designed clinical trials; as of 2013, evidence was insufficient to know whether rTMS is safe or effective for ALS. One 2016 review of stem-cell therapy trials found tentative evidence that intraspinal stem cell implantation was relatively safe and possibly effective. A 2019 Cochrane review of cell-based therapies found that there was insufficient evidence to speculate about efficacy. Masitinib has been approved as an orphan drug in Europe and the United States, with studies ongoing as of 2016. Beta-adrenergic agonist drugs have been proposed as a treatment for their effects on muscle growth and neuroprotection, but research in humans is insufficient to determine their efficacy. Cause
With the discovery that TDP-43, FUS, and  C9orf72 can cause ALS as well as related forms of frontotemporal dementia (FTD/ALS) there has been intense effort to understand how these mutations cause disease, and whether other protein dysfunction may be important.