Ali Simms is doing great, despite her muscular dystrophy diagnosis.

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Years after being diagnosed with a rare form of the illness, known as Titin Muscular Dystrophy, the daughter of Teen Mom 2 stars Leah Messer and Corey Simms is enjoying the winter weather -- and running so much that her father had to slow her down.

"Twins are doing great," Simms' father, Jeff, wrote on Twitter on Tuesday. "Corey had to tell Ali to slow down recently when she was running."

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In late 2009, Messer and Simms welcomed twin girls, Ali and Aleeah. Right away, the couple knew something was a bit different when it came to Ali. After years of doctor's appointments, the since-divorced pair found out Ali was suffering from Titin Muscular Dystrophy, which would eventually restrict her to a wheelchair.

While Messer and Simms decided to get Ali a wheelchair sooner rather than later, the 5-year-old only uses the chair in certain situations, such as a long day at the zoo.

Following Teen Mom 2 season 5, Messer and Simms, who had previously got along well when it came to co-parenting the twins, began feuding. Eventually, the former pair landed in court, where a new custody arrangement was established.

Messer and Simms will appear together on the upcoming Teen Mom 2 season 6, which recently began filming. No premiere date has yet been set.