Thanks for you question. I’ll try to clarify a bit.

The correlation itself doesn’t support any genetic source. That’s similar to the argument concerning correlation and causation I wrote about earlier. However, correlation is a descriptive measure, and is very useful for researchers starting to dissect a disease. They want to understand everything the can about the origins and manifestation of a condition, so correlations with other diseases are part of that.

In this instance the genetic link is made because not only are the two conditions, depression and migraines (in particular migraines with aura) correlated, but because they both have a high heritability, which suggests that genetics are playing more than just a random role in the cause of both those conditions.

So, High heritability plus high odds ratios leads to the conclusion of a common genetic origin.

However, actual genetic analysis can show a much more complicated picture. For example, many genes contributing to the conditions, which may not even be the same in all individuals.

I cna be confusing, but I hope that clears some things up.

Dr. Rick