( Health.com ) -- After playing just one match , Venus Williams announced Wednesday that she is withdrawing from the U.S. Open . The 31-year-old has had nearly every injury in the book , but she offered an unusual reason this time around : Sjögren 's syndrome , a poorly understood autoimmune disorder that causes joint pain and can deplete energy levels . Williams had played only 11 matches this season because of injuries and illness . `` I am thankful I finally have a diagnosis and am now focused on getting better and returning to the court soon , '' Williams said in a statement . As many as 4 million Americans have Sjögren 's syndrome ( pronounced SHOW-grens ) , according to the Sjögren 's Syndrome Foundation , making it the second most common autoimmune disease after rheumatoid arthritis , and ahead of lupus . Ninety percent of the people with the syndrome are women . Health.com : Signs and symptoms of rheumatoid arthritis . It 's `` a major women 's health problem , '' says Frederick B. Vivino , M.D. , associate professor of clinical medicine at the University of Pennsylvania and chief of rheumatology at Penn Presbyterian Medical Center , in Philadelphia . `` A lot of patients look a lot better than they feel . '' How well are you managing your RA ? Take a test . In Sjögren 's , the white blood cells attack moisture-producing glands . The most common symptoms are persistent dry eyes and dry mouth , but the syndrome can lead to complications including extreme fatigue , joint pain , and problems with the kidneys , lungs , liver , pancreas , and central nervous system . Health.com : 12 nice things you can do for someone in pain . Because the symptoms are similar to those of many other conditions , Sjogren 's is difficult for even the most experienced doctors to diagnose . It often takes years for a patient to receive a diagnosis after first experiencing symptoms . Elite athletes like Williams are no more or less likely to come down with the syndrome , but they may be more likely to receive an earlier diagnosis . `` An elite athlete might notice symptoms sooner , '' Vivino says . `` When you 're running around huffing and puffing , your mouth is more likely to dry out sooner . Another important symptom -- fatigue -- will slow them down and affect their performance . And if they develop joint and muscle pain [ that ] persists , that leads to further testing to try to figure out what 's wrong . '' Health.com : Pain relief for athletes -- what works best ? There is no known cure for Sjögren 's syndrome , but symptoms can be managed with both over-the-counter products like artificial tears and sugar-free lozenges and prescription immunosuppressive drugs . The condition disappears suddenly in about 5 % of cases , but the majority of people have lifelong problems . That does n't necessarily mean Williams is done with tennis for good . `` Most manifestations are treatable and in most cases we can restore people to healthy and productive lives , '' Vivino says . `` Whether we can return an elite athlete to competition , that 's another story , but we do feel the treatment makes a big difference . '' Copyright Health Magazine 2011 .
Venus Williams played only 11 matches this season due to injuries and illness . As many as 4 million Americans have Sjögren 's syndrome . Ninety percent of the people with the syndrome are women .