Dyslexic-type symptoms?

My fiance (22 years old) has never had any dyslexic symptoms growing up. But recently, while writing, he'll switch letters around or skip them completely. He realizes afterwards but can't help it while he writes, it's been frustrating him so I am looking for answers. Why could this be? I read that dyslexia is something you're born with and not something you develop, so what could be causing this problem? Any information would be great, thanks.