If you like Stranger Things, you probably love Gaten Matarazzo. The actor, who plays Dustin, often shines in a show that is somewhat beset by incoherent characterization. Other than Eleven, he's the kid with the most pulse. Until recently, he hasn't had occasion to publicly discuss his life with cleidocranial dysplasia, a rare condition that affects how bones and teeth develop. That can include delayed development of adult teeth, which may be peg-like, and underdeveloped or absent collarbones, according to the U.S. National Library of Medicine. It is literally a one-in-a-million disease. "There's a one in a million chance that you have of getting it – most likely you get it from a parent, but it just happened for me," Matarazzo tells People. "I have a very mild case so it doesn't affect me as much, but it can be a very difficult condition to have." Matarazzo doesn't face as many consequences that severe sufferers do, which include a litany of surgery on the back and face. He's had a few mouth surgeries, but tries to see the lighter side of his diagnosis. That includes a trick in which he can move his shoulders to the midpoint of his body. "People are like, 'Well you can do these cool things with your shoulders,' " he tells People. "That part's cool about it." As if you needed another reason to love Matarazzo: He confronts a hyper-rare genetic disease with the same aplomb he brings to the news that his on-screen friend is trapped in a parallel reality occupied by faceless monsters.