Depression and Bipolar: Looking at the Positive While Inadvertantly Demonstrating the Negative

I wanted to critique this study which I admittedly struggled to get my head around, so I needed to get help from one of the authors on Twitter. In short, it takes data from two previous studies of depression and bipolar disorder and recombines them. Here is his given explanation:

The combination of the MDD and the bipolar data (which have not been combined in this way before). That is, we are seeing some loci have statistical evidence for "MDD or bipolar" versus control individuals that we haven't seen when looking at either individually so far.

I'm not really sure if that is what they established even on its face since, as I understand it, they simply combine the data from the two studies and perform new GWAS's for both Bipolar Disorder and Depression, creating a new case vs. control for both (I welcome the authors giving a better explanation than I'm putting forth, lest I be accused of creating a straw man. I really just don't fully understand the underlying premise). In doing so, they came up with 15 new loci related to these disorders without using any new data. I believe the point here is to show that bipolar disorder and depression have some genetic commonalities that were demonstrated. They go on to assess these further, but I suggest maybe the lede was buried here and that the study demonstrated another, perhaps more plausible, conclusion: That the original significant loci were false positives, as are these. Let me explain below the fold: