As I read the decision, this ruling directly impacts the current patents of GHDX. The ruling is that you can not patent the observation of a correlation between natural phenomena to use to make diagnostic recommendations. That is exactly GHDX's business.
Consider this account of the oral arguments and see if it sounds similar to you:
A patient, he posited, has a headache, and takes aspirin for it. An “amazing thing” happens: by looking at the patient’s little finger, one notices that it is changing color. If it is one color, a doctor concludes, the patient took too little aspirin, but if it is a different color, the conclusion is that the patient got too much. “Now,” suggested Breyer, “I’ve discovered a law of nature and I may have spent millions on that. And I can’t patent that law of nature.”
Unfortunately, I believe there may be some room for misinterpretation and, so, this ruling could give GH some headaches. But my reading of this would allow for GH to claim sufficient invention with their products.
See pp 12 and 13. The discussion of Flook and Diehr. GH's patents "explain how the variables used in the equations are to be selected.". There is "inventive concept" in the methods of finding and associating the "laws of nature" (in our case, genomes) with the nature of one's illness.
Prometheus used one formula of a known natural process, suggested values on which to make decisions, and objected when Mayo suggested their own different values. Mayo has a right to advance scientific knowledge using that well known law of nature.
If Mayo went to the trouble of identifying genomes associated with breast cancer, including any "discovered" by GH, and back tested them to find their own algorithm that predicted something useful in treatment decisions, and THEN tested that algorithm against real cases so that they gained FDA approval, then GH would have no claim against them. (at least, that is how I read this decision). But that is a hurdle sufficiently high.