Reversing of
letters can be due to dyslexia or due to dysgraphia.
In the former, speech is not affected.
In the latter, a person has difficulties framing his thoughts—so stuttering is possible. It can be the result of a visual processing disorder.
Also if stuttering developed in adulthood, it can be due to anxiety, head injury, tumor, stroke or drug use. All these may affect speech and learning, and visual perception of letter.