Amyotrophic lateral sclerosis, or ALS, is a condition that causes nerves responsible for controlling a wide variety of voluntary movements to progressively deteriorate over time.
It was once commonly referred to as Lou Gehrig's disease, named after a popular American baseball player who was diagnosed with the condition in the mid-20th century. Today it's more commonly associated with the famous physicist, Stephen Hawking, who was diagnosed with ALS at age 21.
Though relatively rare, ALS is the most common of all motor neurone diseases, potentially affecting as many as one in every 12,000 people at some point in their life.
From early symptoms of muscle twitches and stiffness, proceeding into weakness in the limbs, most of those with the condition eventually experience general body paralysis and respiratory failure within two to four years. In around one in ten cases, people with the disease survive longer than a decade.
What causes ALS?
In around nine out of 10 cases, a diagnosis of ALS can't be easily linked with specific genetic or environmental factors. Although these 'sporadic' cases make up the majority, the remaining 'familial' examples do suggest there could be a genetic role for the disease.
Investigations of the 10 percent of cases with a family history have revealed mutations that either give rise to the condition or affect how it manifests. Nearly half of those cases are linked with a gene labelled C9ORF72, which is responsible for making a protein found in motor neurons. Around a quarter of cases are associated with SOD1, a gene involved in making an enzyme that binds copper and zinc ions.
Even if DNA influences the condition's development and progress, it's clearly a complex interplay of different combinations of genes we inherit, mutations, and environmental factors.
What treatments are there for ALS?
So far, researchers haven't found a safe or efficient way to undo the damage caused by ALS.
The best modern medicine can do right now is reduce the impact of its symptoms and control the risk of complications.
Medications that block the release of the neurotransmitter glutamate have been shown to slow the disease's progress somewhat. A relatively new treatment called Edaravone was approved by the FDA in 2017, though it's not known exactly how it helps treat ALS.
Physiotherapy and low-impact exercise might also keep affected muscles stronger for a little longer, improving motor functions in the short term.
Where movement is inevitably lost, technology is stepping in to assist. Stephen Hawking's means of communicating and moving were controlled largely by movements in his cheek muscle in his later years; new technologies might use eye movements, or even brain activity to engage computers that can talk, walk, and manipulate objects.
All Explainers are determined by fact checkers to be correct and relevant at the time of publishing. Text and images may be altered, removed, or added to as an editorial decision to keep information current.