The world lost one of its most brilliant scientific minds Wednesday, when legendary physicist Stephen Hawking died at age 76.
Hawking’s cause of death was likely amyotrophic lateral sclerosis, or ALS, a neurodegenerative disease that wears away at nerve and muscle function over time. He was first diagnosed with ALS more than five decades ago, at age 21, and was initially given just a few years to live — making the very nature of his long, illustrious career as much of a scientific marvel as the theories and discoveries it yielded.
Here’s what to know about ALS, and what may have allowed Hawking to beat the odds for so long.
ALS, also known as Lou Gehrig’s disease, is a progressive neurodegenerative disease that erodes motor neurons — cells in the brain and spinal cord that control muscular function — until it becomes difficult or impossible for a person to walk, talk, speak, swallow and breathe, according to the ALS Association. ALS symptoms often begin with slurred speech or muscle weakness and twitching, according to the Mayo Clinic, and get worse over time. The rate at which a person’s condition degrades can vary quite a bit, though the average survival time is three years after diagnosis, the ALS Association says.
This article was originally published here.