Selena Gomez shared an emotional Instagram post about the kidney transplant she received from her friend, actress Francia Raisa. (The Washington Post)

In the world of celebrities, there are diseases such as HIV/AIDS and breast cancer that are very “popular” and well understood, thanks to years of fundraising and awareness campaigns by stars. And there are those diseases that are less so. Lupus, an autoimmune disorder that can damage organs, is in the second category.

When Selena Gomez shocked her 126 million Instagram followers on Thursday by revealing that she had disappeared from the public eye this summer because she was getting a kidney transplant because of lupus, her fans had many questions.

Many wondered how someone so young and seemingly healthy — Gomez, 25, made numerous appearances this spring and looked radiant — could suddenly need such a radical surgery. Some commented that perhaps her case was atypical.

It's the opposite. Lupus, in which the body's immune system turns against itself, strikes women of child-bearing age at the highest rates. Those who are minorities are especially vulnerable. Only about 10 percent of white women with lupus progress to kidney failure; about 20 to 40 percent of African American or Hispanic women do so.

Gary Gilkeson, associate dean at the Medical University of South Carolina and chairman of the Lupus Foundation of America's medical-scientific advisory committee, says the disease is challenging to diagnose, because, in its early stages, it looks like many other conditions. People with lupus may first experience fatigue, joint pain or a little bit of rash on their bodies and can go for a long time before their doctors realize it is more serious.

“Many people see two or four physicians before it is picked up that’s what the problem is. It is difficult to diagnose early on, but the earlier the diagnosis the better the chance of us catching it before it gets too out of hand,” Gilkeson said.

I’m very aware some of my fans had noticed I was laying low for part of the summer and questioning why I wasn’t promoting my new music, which I was extremely proud of. So I found out I needed to get a kidney transplant due to my Lupus and was recovering. It was what I needed to do for my overall health. I honestly look forward to sharing with you, soon my journey through these past several months as I have always wanted to do with you. Until then I want to publicly thank my family and incredible team of doctors for everything they have done for me prior to and post-surgery. And finally, there aren’t words to describe how I can possibly thank my beautiful friend Francia Raisa. She gave me the ultimate gift and sacrifice by donating her kidney to me. I am incredibly blessed. I love you so much sis. Lupus continues to be very misunderstood but progress is being made. For more information regarding Lupus please go to the Lupus Research Alliance website: www.lupusresearch.org/ -by grace through faith

A post shared by Selena Gomez (@selenagomez) on

No one knows exactly what causes lupus. More than 60 genes have been identified as putting people at higher risk, but environmental factors also seem to play a large role. Some scientists believe that certain viral infections may trigger lupus. There is evidence that different organic pollutants and even exposure to radiation through substances like uranium could activate the disorder.

Some of the most important research on lupus going on right now involves early identification of people who may develop lupus before they have full-blown symptoms. The National Institutes of Health is funding a study that looks at people with a certain blood-based indicator and one or two symptoms that suggest lupus. Some of those people will progress to the disease and some will not, and the goal is to try to figure out the difference between the two groups.

While kidney failure is a serious, life-threatening complication of lupus, the number of people having successful treatment with transplants is increasing. People have two kidneys but need only one. So a growing number of patients have managed to find friends or family members who are matches and can donate, or they participate in “kidney exchanges” in which a friend of one patient will donate to a stranger who is a match in exchange for the second patient's friend donating to the first patient.

In Gomez's case, the donor was one of her BFFs, actress Francia Raisa, who has appeared on “The Secret Life of the American Teenager” and played a hockey player-turned-figure skater in one of the recent remakes of “The Cutting Edge.”

The good news for patients like Gomez, Gilkeson said, is that many women with lupus who undergo transplants go on to live long, healthy lives. There's something about the immunosuppressants that transplant patients must take to prevent rejection of the new organs that also keeps lupus at bay.

“I think it's important to emphasize that lupus patients can lead relatively normal lives,” Gilkeson said. “She will be able to resume her career, go to college if she wants, and having children is possible.”

In the Instagram post in which she shared a picture of herself and Raisa lying side-by-side on hospital beds, Gomez said she hopes to share more of her story in the coming months and directs her followers to the Lupus Research Alliance website.

“Lupus continues to be very misunderstood,” Gomez wrote, “but progress is being made.”


Pop star Selena Gomez, left, and her friend and organ donor, actress Francia Raisa. (Invision/AP)

Read more:

‘She gave me the ultimate gift’: Selena Gomez tells emotional story of her kidney transplant

She rejected chemotherapy and chose to die of cancer — so she could give birth to her child

Melinda Gates decries ‘loss of U.S. leadership’ in global aid