What is ALS? As Hollywood star Eric Dane reveals heartbreaking diagnosis

Euphoria and Grey's Anatomy's Eric Dane has announced he's been diagnosed with amyotrophic lateral sclerosis (ALS).

"I have been diagnosed with ALS,” he told People. “I am grateful to have my loving family by my side as we navigate this next chapter.” 

The 52-year-old is married to Rebecca Gayheart and the couple share two children, Billie Beatrice, 15, and Georgia Geraldine, 13.

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“I feel fortunate that I am able to continue working and am looking forward to returning to set of Euphoria next week,” he added. “I kindly ask that you give my family and I privacy during this time.”

Dane — who stars as Cal Jacobs in the hit HBO series — is set to begin production of Season 3 on April 14. 

ALS, also known as Lou Gehrig's disease, is a rare neurodegenerative disease that affects nerve cells in the brain and spinal cord and causes progressive paralysis of the muscles.

The ALS Association writes that "Amyotrophic" comes from the Greek language. "A" means no, "myo" refers to muscle, and "Trophic" means nourishment.

Altogether, amyotrophic means "no muscle nourishment,” and when a muscle has no nourishment, it "atrophies" or wastes away.

"Lateral" identifies the areas in a person's spinal cord where portions of the nerve cells that signal and control the muscles are located.

As this area degenerates, it leads to scarring or hardening ("sclerosis") in the region.

Motor neurons go from the brain to the spinal cord and from the spinal cord to the muscles throughout the body, but the progressive degeneration of the motor neurons in ALS eventually leads to their demise.

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When the motor neurons die, the brain can't initiate and control muscle movement is lost. When voluntary muscle action is progressively affected, people may lose the ability to speak, eat, move and breathe.

Patients first experience twitching or weakness in a limb, often followed by slurred speech. 

The motor nerves affected when you have ALS are the motor neurons that provide voluntary movements and muscle control.

Examples of voluntary movements are making the effort to reach for a phone or step off a curb. These actions are controlled by the muscles in the arms and legs.

There are two different ways cases are categorized.

For about 90% of all cases, there’s no known family history of the disease or presence of a genetic mutation linked to ALS.

For 5-10% of all cases, there’s a known family history of the disease. This is often called familial ALS.

There's new scientific understanding about the physiology ALS in recent years.

There are currently seven drugs approved by the U.S. Food and Drug Administration (FDA) to treat ALS and its symptoms: Qalsody, RELYVRIO, Radicava, Rilutek, Tiglutik, Exservan and Nuedexta.

There's no cure for ALS, and people usually live three to five years after diagnosis, according to the Muscular Dystrophy Association.

However, some patients can live decades.

In addition to Dane, other notable celebrities who have been diagnosed with ALS include Aaron Lazar, John Driskell Hopkins, Eric Stevens, Joe Bonsall, Roberta Flack, Kenneth Mitchell and Stephen Hawking.