Bright, spacey children get tested to discover what's wrong. In my era, I kept getting hearing tests at the request of the school. When my son Ben was in school, this had escalated to fancy attention and neurological tests. Just daydreaming, friends.
One odd fragment of the testing was when the neurologist, reading the sleep-deprived EEG, noted that Ben would have trouble making his left and right hand do different things. Well, that explained why this musically talented child was unable to get very far on piano, so we switched to voice. Too late.
I found it a fascinating idea. I was a guitarist as well as a singer, and always claimed I had to work twice as hard to be half as good as everyone else. And that description of the neurologist's described my limitation. I was a decent rhythm guitarist, because the left and right hands had to do approximately the same thing. This has run around in my head over the last dozen years; I finally got around to researching it.
It seems there are inhibitory fibers which run between the two sides of the brain – intercallosal – which reduce “mirror movements,” in which the nondominant hand involuntarily picks up the movement of the dominant hand. Ben and I have a reduced number of these fibers, seemingly. I didn't discover any information on heritability, but we have a good anecdotal case to start with.