It is generally estimated that there are 30,000 people in the United States living with ALS
at any given time. The number is estimated at around 450,000 worldwide. These numbers are hard to accurately determine because there is no standard measure, the disease takes time to diagnose, and availability of adequate medical care for neurological diseases varies by country. Generally speaking, someone gets diagnosed with ALS
every 90 minutes. There are many national efforts, including one in the US, to count and/or register people living with ALS.
There are two broad categories of ALS - sporadic ALS (sALS, essentially of unknown cause) and familial ALS (fALS, with a direct genetic cause). Familial ALS makes up about 10% of all ALS cases and occurs when specific genetic mutations are inherited and passed down through generations. More than 30 genes have been identified with mutations associated with ALS.
The remaining 90% of cases are sporadic ALS, meaning there is no known history of the disease in the family. There are many theories outlining potential causes of ALS including oxidative stress mitochondrial dysfunction, immune system over activity, glutamate toxicity and toxic exposures. ALS appears to affect men at a higher rate than women below the ages of 65. For men and women over the age of 70, incidence appears to be the same. It is important to note that familial ALS and sporadic ALS are seemingly indistinguishable clinically from one another. For more information, visit the "What is ALS?" section of the website.
PLS neurodegeneration is restricted to only upper motor neurons. Whereas, an ALS diagnosis requires the observation of progressive loss of both upper and lower motor neurons. Publications suggest that PLS tends to be a slowly progressing disease, but progression may advance to involve lower motor neurons as well. Due to this, PLS diagnosis is often altered to ALS.
A comprehensive report conducted by the National Academies' Institute of Medicine (IOM) in 2006 supports the association between service in the US military and increased risk of developing ALS. The IOM reviewed and evaluated all relevant scientific literature on ALS and veterans. It concluded that there exists "suggestive evidence of an association between military service and later development of ALS."
Since 2000, studies have been conducted to assess the ALS incidence rate in Gulf War veterans. Most notable was a study funded by the US Department of Veterans Affairs and the US Department of Defense. It concluded that those deployed in the first Gulf War (1990-1991) were twice as likely to develop ALS as their non-deployed counterparts, and potentially, at younger ages. Air Force veterans, it determined, faced the highest risk, at 2.7 times that of those not serving.
In 2005, The Harvard School of Public Health broadened the case for ALS's military relevance. Its study found that men with a history of any military service in the last century were about 53% more likely to die of ALS than men in the general population. In July 2008, in response to the evidence, Secretary of Veterans Affairs Dr. James B. Peake announced that ALS is now considered a presumptively compensable illness for all veterans with 90 days or more of continuously active service in the military.