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Tennis superstar Venus Williams’ announcement Wednesday that she was withdrawing from the U.S. Open due to a medical condition shook the sports world. Williams revealed that she has been diagnosed with Sjögren’s syndrome – a disease that is not well-known and therefore left her fans with many questions and fear for her health.

FoxNews.com talked with the CEO of the Sjögren’s Syndrome Foundation, Steven Taylor, to get answers about this syndrome—which is more common than you may think.

What is Sjögren’s syndrome?

Sjögren’s syndrome is an autoimmune disease that affects moisture production glands in a person’s body. The syndrome is life-altering – not life-threatening. Multiple systems and organs are affected, basically all the different moisture glands throughout body. All the moisture glands are being attacked by your immune system. It can vary from very mild to very severe.

What are the symptoms?

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The most common symptoms are dry mouth, dry eye, joint pain and fatigue. The central nervous system and other body systems and organs like the lungs and liver can be affected also.

How is it diagnosed?

It is diagnosed with a classifications criteria system—including a blood test, lip biopsy, tear testing and saliva testing. A rheumatologist is the lead doctor for patients—typically they are the most common to diagnose it. The challenge is the symptoms can mimic so many other diseases. Venus has said she thought it was allergies, asthma—it can be mistaken for all different things. On average, it can take over six years to diagnosis the disease.

How common is Sjögren’s syndrome?

It is one of the most common unknown diseases. Four million Americans have it, but most have never heard of it. More women have Sjögren’s syndrome than breast cancer—90 percent of those that have it are women. The challenge is that only about one million are diagnosed.

Is Sjögren’s syndrome fatal?

It does claim some lives because of complications, but most live a regular lifespan. The syndrome alters their life. They may have to go on disability because they can’t work anymore. Patients have to delegate how they save their energy and what they are able to do each day.

What is the treatment?

There is no specific prescription, so it is just a variety of products, a lot of over-the-counter products, like sprays and gels for dry mouth and eyes and then ibuprofen and things like that. Some have to take autoimmune suppressant drugs. It just involves lots of different products and working with a rheumatologist. Every patient has a different treatment plan – there is not one set plan.

Will Williams be able to return to tennis?

That is the million dollar question. We surely hope she will be back. She will have to use her resources to figure out what her priorities are. Patients usually have to give up something because they need to save their energy. We have a lot of athletes who have to give up marathons, and other sports activities. It is not a disease that makes you look sick – she looks great – but it will progress for her. On the other hand, we have patients who have still been able to continue running marathons. So there is hope for her, but she will have to have a partnership with her doctor.

Can Sjögren’s syndrome hinder a woman’s ability to have children?

They can have children but there is a little more risk. The main increased risk for a child of someone with Sjögren’s syndrome is fetal heart block. That is one thing to watch out for, but they can go on to have kids.

What will be Williams’ biggest challenge with Sjögren’s syndrome?

The challenge is there is no one progression. You can stay the same for 30 years or you can progress quickly and become very sick. You just never know. Patients tell me the worst part of the syndrome is the fear of not knowing what tomorrow will be. There is no cure and no treatment – there is no end. It will continue for the rest of Venus’ life.

Researchers do not know exactly what causes this syndrome, but they believe it could be a combination of genetic and environmental factors.