It causes overgrowth in bones, skin and other tissues. Those organs grow out of proportion with other tissues in the body.

For Rosnick, the most obvious features impacted by the condition are his fingers. Three on each hand are overgrown, maybe six inches long and the width of an extra-wide thumb.

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And Dylan Rosnick, large fingers and all, wanted to play baseball. So his father went to work dismantling and rebuilding baseball gloves until one thing became clear. Just like Rosnick, a senior at Champe High in Aldie, Va., had taught himself to tie his shoes and button his shirt, he was going to teach himself to be a true ballplayer — a pitcher at that.

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“I just worked it out,” he says now.

Great pitchers are often defined by one dominant pitch developed over years of trial and error. Take Mariano Rivera’s cutter, Randy Johnson’s fastball, Roger Clemens’s splitter.

Rosnick has that, just not by choice. His fastball tops out at 65 mph, well below what high school hitters are used to seeing, because his fingers spend more time wrapped around the ball, reducing his velocity. But when Rosnick uses those larger fingers to apply a little pressure to either side of the baseball, it causes it to dance across the plate.

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“When we saw that, it jumped out at us,” Champe Coach Joe McDonald said. “And not in a bad way. We thought, what could we do with that?”

Actually, quite a lot. Rosnick was just selected by Virginia’s Conference 22 coaches to the division’s second team.

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Rosnick’s curveball flutters out of his hand, then breaks late toward the plate like a lunging cobra. His splitter runs in on a lefty’s back foot and seemingly vanishes about 10 feet from the plate.

The pitches are such a change of pace from the rest of Champe’s pitching staff that Rosnick doesn’t throw a traditional off-speed pitch. Why should he?

McDonald has used Rosnick as the Knights’ long-relief pitcher. Rosnick has registered the second-most innings on the team behind his twin brother, Ryan, who doesn’t have Proteus syndrome.

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He has a 3.70 ERA and boasts a 2-0 record.

“We coach him the exact same way as everyone else because he’s just as good as everyone else,” Champe pitching coach Kenny Moreland said.

Rosnick will attend Christopher Newport University next year in hopes of becoming an elementary school teacher after graduation. Moreland, who pitched at Newport, already has called coaches to tell them to bring Rosnick out for a tryout.