"Unsupervised clustering of these patient samples revealed three distinct molecular subclasses of PE. This included a "canonical" PE subclass demonstrating elevated expression of known PE markers and genes associated with poor oxygenation and increased secretion, as well as two other subclasses potentially representing a poor maternal response to pregnancy and an immunological presentation of preeclampsia."
So for just about forever, they've said this syndrome was "multifactorial" - many different things can cause it. This study into the underlying genetics isolated three broad categories of suck that can predispose a pregnancy to preeclampsia. One was of a set of genes we understand pretty well at this point - poor oxygenation of the placenta leading to unregulated soluble flt, vascular damage, and all the other things that fit into a classical preeclampsia profile - and the other two were "molecular clusters", or sets of genes that tended to appear in the analysis next to one another, but which we don't always understand well yet. (There has been a lot more work on the first group in pregnancy than on the second two.) Those were "poor maternal response" - probably underlying conditions like kidney disease that cause slightly different downstream effects from the preeclampsia driven by shallow implantation - and "immunological presentation" - which is HELLP, and probably women with genetic conflict with the partner that compromises their ability to host a fetus (think women whose babies are a good size, and who have no obvious underlying conditions, but who develop severe rapid-onset disease with no warning.)