“Teen Mom 2” star Leah Messer and her ex-husband, Corey Simms, were given some devastating news about their daughter, Ali, who has muscular dystrophy, during a preview for Season 7. Ali’s condition has worsened, and she may not be able to walk by the time she is 7 years old, her doctor told the MTV reality stars. Ali was 6 at the time of filming.

Dr. Tsao, a neuromuscular specialist, told the parents he wanted to see Ali because she was falling and hitting her knees often. When Simms says his daughter falls at least five times a day, Tsao gives a grim prognosis. He tells the reality stars to fix Ali’s wheelchair, which she hasn’t used for three months.

“Her strength is still quite decent,” the doctor says. “But once she’s getting to age 7, then gradually, the maturity affects her. Then she may very slowly get weaker.”

Eventually, she may need to be in the wheelchair full time. “So I think that she needs to have [a] power wheelchair all the time,” he said. “So the most important thing is to fix her power wheelchair.”

Tsao suggests they go through Make-A-Wish Foundation to fix the chair, because many children who have Ali’s medical condition qualify. “If you haven’t done that, you should apply,” he said.

Not happy with hearing her daughter might spend the rest of her life in a wheelchair, Messer, 23, suggests Ali make that decision for herself when she’s older. “She’s going to get weaker over time. Close to 7 it starts to go downhill,” the doctor says.

“She has muscular dystrophy,” Tsao says. “If she gets weaker, then she may not enjoy much either.” Tears well up in Messer’s eyes as the promo comes to an end.

To find out what happens with Ali, don’t miss the premiere of Season 7 of “Teen Mom 2” when it debuts on Monday, March 21, at 10 p.m. EDT on MTV.

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