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This week on the emotional finale of Teen Mom 2, Season 5, Leah Messer and her ex-husband, Corey Simms, finally got to the bottom of their daughter Ali's muscular dystrophy diagnosis. Leah and Corey were told that Ali had a rare form of the disease a while back, but they didn't know exactly what gene caused the condition. They were under the assumption that Ali had Ullrich congenital muscular dystrophy — a severe form that would likely cause her to lose muscle strength and respiratory function.

However, after further testing Leah and Corey learned that Ali actually has Titin muscular dystrophy, a super-rare form that has only ever been found in adults. This means Ali is literally the only child in the world with the disorder! "This is a new gene, and in fact doctors throughout the world are just starting to learn about this gene mutation, which can affect the heart or breathing," Ali's doctor explained to Leah and Corey.

The doctor went on to say that there are currently less than 20 people in the world with Ali's particular form of muscular dystrophy, all of them adults. So, what does this mean for Ali? According to the doc, Ali might develop respiratory difficulties and heart problems. As far as prognosis goes, many people with Titin muscular dystrophy can live well into their fifties or longer.

The good news is that most people with Titin muscular dystrophy don't develop heart or breathing conditions until much later in life, though the doctor did recommend that Ali be seen by both a cardiologist and a pulmonologist (a respiratory specialist) every year.

We can't imagine how hard it must have been for Leah and Corey to hear this news — but hopefully research on Titin muscular dystrophy will improve by leaps and bounds in the next few decades.

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