What to know about cyclic vomiting syndrome that affects Chandra Wilson's daughter

— -- This week, "Grey's Anatomy" star Chandra Wilson is shining on a light on a rare condition that has affected her daughter called cyclic vomiting syndrome, or CVS.

Since it took nearly a year for Wilson's daughter to receive a confirmed diagnosis, she is highlighting the disorder to help other people who may be suffering with the symptoms.

Here are some key facts about CVS.

What is cyclic vomiting syndrome? The syndrome is a condition where a person has sudden and repeated bouts of nausea, vomiting and exhaustion, according to Cleveland Clinic. There is no apparent cause.

Usually these symptoms occur early in the morning and an attack can last from several hours to several days. Both men and women can be affected, but it is more common in children than adults.

CVS affect the upper gastrointestinal tract, which includes the mouth, esophagus, stomach and part of the small intestine, according to the The National Institute of Diabetes and Digestive and Kidney Diseases, part of the National Institutes of Health (NIH).

Symptoms include repeated episodes of severe nausea, lack of appetite, sensitivity to light, pain in the abdomen, severe fatigue and severe headaches.

What is the cause? It is unclear why the disease occurs, but one theory is that a person has abnormal function of their mitochondria, the energy powerhouse in their cells. According to the Cleveland Clinic, changes in the mitochondrial function have been observed in people with CVS and they may be one cause for the condition.

Additionally, hormonal imbalances, nervous system problems or gastrointestinal dysfunction may also lead to developing the syndrome, according to the Cleveland Clinic.

People with a history of migraines may be more susceptible to the disease, according to the NIH.

How is an episode triggered?

Although there is no specific cause of CVS, the NIH says there are certain instances that may lead to a cycle of vomiting. Both physical changes and emotional stress can trigger CVS.

"Emotional stress, anxiety, or panic attacks -— for example, in children, common triggers of anticipatory anxiety are school exams or events, birthday parties, holidays, family conflicts, or travel," the NIH says on their website.

Physical changes in the body's systems such as infections and flu, as well as motion sickness, heat or physical exhaustion and even a regular menstrual cycle are some of the conditions that can lead to an episode, the NIH says. Food additives like caffeine, nitrites and MSG can also be triggers.

Is there treatment?There is no known cure for the syndrome, but people affected can receive treatments to mitigate symptoms, such as nausea, and to treat other conditions that can contribute, like migraines.

How many people are affected? Approximately 3 in every 100,000 children are diagnosed with CVS, according to the Cleveland Clinic. However, it's difficult to estimate the total number of people affected by the syndrome because it is not always reported. The Mayo Clinic estimates that 2 percent of school-age children may be affected and cases are increasing in adults according to research.