Actually we do know quite a bit about ALS
Rest in Peace, and condolences for families and friends of patients who died due to Amyotrophic Lateral Sclerosis (ALS).
This post was a follow up to: Amyotrophic Lateral Sclerosis (ALS) and CBD Receptors. transcendingsquare.com/2014/08/23/.
The Life Extension Foundation is a non-profit organization focused on research into preventative health strategies. The company does sell supplements, books, and a few other products but it also helps fund research in preventative health care. The foundation publishes an academic type journal and an article from the journal is available on their website which provides a review of the current theories and research available regarding Amyotrophic Lateral Sclerosis (ALS). 
The article ends with a quote or two about the limited effectiveness and negative side effects associated with the medication that is currently prescribed for ALS patients. The sad point is that at least then the doctor can feel like they provided a service by writing a prescription but if it doesn't really help slow progress of the disease and adds negative side effects then is that prescribing doctor really "Doing no harm."?
The article doesn't provide vitamin or supplement recommendations or provide other preventative guidance. It is a review of current research which did provide enough information to suggest to me several strategies that might help me reduce my risk of developing ALS. I'm motivated because I fall into one of the 'you may be at more risk for ALS if you also have this condition' categories.
Studies suggest that ALS is more associated with some autoimmune and chronic infectious diseases and with some nutrient deficiencies or imbalances and with exposure to some environmental toxins.
A few points gleaned from the article that might help me reduce my risk of developing ALS:
Avoid mercury, lead, aluminum, manganese and other heavy metal toxins.
Be careful if working with herbicides and pesticides to reduce exposure.
Have adequate intake of calcium and magnesium - in balance. Excess calcium and too little magnesium may increase degenerative calcification of the central nervous system.
Avoid excess intake of free glutamates. There are many sources of free glutamates in the diet as they are used as flavoring agents. MSG is one better known example. *The article doesn't recommend avoiding glutamates, it mentions that ALS is associated with glutamate toxicity. One study found plasma levels of glutamate to be significantly elevated in ALS patients compared to controls (Plaitakis et al, 1993). One theory suggests that there may be a glutamate transport problem that allows the elevated levels to accumulate.  *Having adequate zinc and magnesium levels helps the cells control intracellular glutamate levels. , magnesium also helps control transmembrane movement of the other electrolytes: calcium, sodium and potassium.  ALS is highly linked with glutamate. One proposed mechanism is a defective glutamate transport system that permits neurotoxic levels to build up (Onion 1998). A study showed significant elevations (by about 70%) of plasma levels of glutamate in ALS patients as compared to controls (Plaitakis et al. 1993). - See more at: http://www.lifeextensionvitamins.com/amlatscleral.html#sthash.ErWUopES.d
ALS is highly linked with glutamate. One proposed mechanism is a defective glutamate transport system that permits neurotoxic levels to build up (Onion 1998). A study showed significant elevations (by about 70%) of plasma levels of glutamate in ALS patients as compared to controls (Plaitakis et al. 1993). - See more at: http://www.lifeextensionvitamins.com/amlatscleral.html#sthash.ErWUopES.dpuf
Have adequate but not excessive intake of selenium as it helps the body remove mercury. Two Brazil nuts per day provide about 200 micrograms of selenium which is the recommended daily goal. Excess selenium can cause toxicity symptoms so be careful not to take supplemental one-a-day or other mixtures that contain selenium in addition to taking selenium as an individual supplement or in addition to eating Brazil nuts regularly. Toxicity wouldn't occur in a few days but might develop if multiple sources were eaten over a longer time period.
Growth factor deficiency may be involved in development of ALS. Touch is important for stimulating human growth factor. Therapy pets and massage may also help stimulate internal production of human growth factor. *The article doesn't mention the therapeutic benefits of touch. It only mentions that reduced growth factors are an underlying problem associated with ALS and pharmaceutical sources have been found helpful for slowing progress of the disease in some (but not all) studies. However touch can also help stimulate innate production of growth factors without needing a pharmaceutical company. 
Spinal compression may increase risks of a similar nerve degeneration problem that can resemble ALS so /speculative/ regular exercise such as swimming might help or regular use of an inversion board at a gentle 10 degree slope might help relieve spinal pressure. /Disclosure, I do use an inversion board and find it helpful for headache and back problems but they can be dangerous so please seek individual guidance regarding their use./
Some infections with long term chronic phases are associated with ALS type symptoms including Lyme's disease, poliomyelitis, HIV/AIDs, and tertiary syphilis.
Some endocrine and autoimmune diseases such as the hyperthyroid condition Grave's disease and Diabetic Amyotrophy are associated with ALS risk. Maintaining lower thyroid levels and avoiding thyrotoxicosis may help reduce risk of developing ALS.
Some other conditions associated with ALS like problems include the neurological diseases: Pick's Disease and Kennedy's Syndrome; and the genetic enzyme disorders: Superoxide Dismutase, Hexosaminidase A, and Alpha-Glucosidase.
If you missed the previous post - adequate cannabinoids/phospholipids are an important factor in protecting against ALS. A list of legal food sources of cannabinoids or phospholipids is included, see: Amyotrophic Lateral Sclerosis (ALS) and CBD Receptors. transcendingsquare.com/2014/08/23/.
Lyme disease and poliomyelitis
Amyotrophic Lateral Sclerosis
Amyotrophic Lateral Scleros
/Disclaimer: This information is provided for educational purposes and is not intended to provide individual health guidance. Please see an health professional for individual health care purposes./