Many scientific studies suggest it and I strongly believe it is, yes (for a subgroup). However, it could be more to the SZ end of the spectrum only. More studies are in support of the idea for SZ, but quite some for BP or a combined group. What is investigated is brain lateralisation, but this is an indicator for left-handedness or ambidexterity.

Some of us talked about it in the Dyscalculia thread. If you are interested and can't find it, tell me and I will give a link.