I'm traveling and can't pull up my genetics test, it's a marker that impacts the corpus collusum and makes it very weakly connected. This leads to the increased risk of several diseases, and a likely increased IQ. It's passed down in the X chromosome. For us it was identified in brain scans, then I got everyone to take genetics tests which confirmed.

From there, I'm guessing you can maybe find something on Google. It's an active area that's still being explored too. From ancedotal evidence we do have schizophrenia run in the family, and we also regularly break 130 on IQ tests - so take it for what you will