Frankly, I read about it, but since I can't be arsed, I'm not going to bother. If its so important to you, you might want to look into it. Unless he sneezed on every letter and left a nose hair, which can be DNA identified by exhuming his bones or something, its completely irrelevant to me. And even then, it would be merely prurient interest.
Islam is an ideology, now whether its founder wrote with his left hand, had a big dick, preferred being on top, did handstands in his sleep, etc are all not relevant to what it is. Its like asking all these questions about Einstein. Who cares?