Sandra Bullock's longtime partner Bryan Randall died at age 57 after privately battling ALS, or Amyotrophic Lateral Sclerosis, for three years, his family said. The news brought new attention to the disease and prompted questions about what the diagnosis means.

ALS is a progressive neurodegenerative disease that affects nerve cells in the brain and spinal cord, making the brain unable to control muscle movement. As the illness progresses, people eventually lose their ability to speak, eat, move and breathe, according to the ALS Association.

It is also known as Lou Gehrig's disease, for the legendary New York Yankees player who was stricken with it in the late 1930s.

In the United States, more than 30,000 people are believed to be living with ALS, and an average of 5,000 people in the U.S. are diagnosed with ALS each year, according to the Centers for Disease Control and Prevention.

"ALS is a devastating illness," Dr. Sandeep Rana from Allegheny Health Network recently told CBS News Pittsburgh. "It's a neurological disease where patients start to get weak. They lose muscle strength. They lose muscle mass."

What causes ALS?

Experts don't know the exact cause of ALS. Only a small portion of cases appear to have a genetic component.

"About five to 10 percent of all ALS cases are familial (also called inherited or genetic). Mutations in more than a dozen genes have been found to cause familial ALS," the National Institutes of Health notes.

Nearly all other cases of ALS are considered sporadic, the NIH explains, meaning the disease "seems to occur at random with no clearly associated risk factors and no family history of the disease."

According to the ALS Association, the disease can strike anyone at any time, but it usually appears between the ages of 40 to 70.

 The average life expectancy with the disease is 2 to 5 years.

ALS symptoms

According to the NIH, early signs and symptoms of the disease include:

• Muscle twitches in the arm, leg, shoulder or tongue.
• Tight and stiff muscles.
• Muscle weakness affecting an arm, leg, neck or diaphragm.
• Slurred and nasal speech.
• Difficulty chewing or swallowing.

As the disease progresses, symptoms of muscle weakness spread to other parts of the body, causing more challenges to daily life, including:

• Not being able to stand, walk or use hands and arms.
• Trouble chewing and swallowing food.
• Trouble speaking or forming words. 
• Difficulty breathing.

"Individuals with ALS eventually lose the ability to breathe on their own and must depend on a ventilator," the NIH says. "Most people with ALS die from respiratory failure."

ALS treatments

Currently, ALS has no cure and there is no treatment to reverse its progression. The FDA has approved several medications, but their benefits are limited.

The search for new answers to fight ALS was the inspiration behind the hugely popular Ice Bucket Challenge a decade ago, which raised over $200 million for research. But patients and families are still waiting for breakthroughs. 

For now, options to help people living with the disease include supportive health care from physicians, home care nurses and other medical professionals. 

"These teams can design an individualized treatment plan and provide special equipment aimed at keeping people as mobile, comfortable, and independent as possible," the NIH explains.

In a statement, Bryan Randall's family thanked the "tireless doctors" and "astounding nurses" who helped care for him, "often sacrificing their own families to be with ours."

Patients may also benefit from physical and occupational therapy; speech therapists, who can help them maintain the ability to communicate; and nutritionists, who can plan and prepare balanced meals that are more easy to swallow.

Artificial intelligence is also starting to play a role in helping ALS patients communicate. CBS News chief medical correspondent Dr. Jon LaPook recently reported on new technology helping patients speak through a process called voice preservation.

In:
• Lou Gehrig's Disease
• ALS