LS,
The studies are small but provocative. Big shifts in the levels of gene expression that, as has been mentioned, differentiate between Fibro, ME/CFS w/ Fibro and Me/CFS without Firbro., etc. There may also be other sub-groups within groups. The NIH grant ought to allow them to look for other genetic markers (so far they've only taken a look at what they felt was the most promising candidates - there is a lot more that they want to look at) and as just as importnat, if not more so, the larger sample sizes made affordable by the grant should help them determine if these preliminary sub-groups are stable.
As for the heritability, that study is interesting/suggestive but needs quite a bit more work (and clearly does not provide a comprehensive explanation for ME/CFS). For starters (and this is huge), all that was looked at was whether or not people diagnosed by their doctors with CFS (no specific criteria mandated due to the nature of the study) were more likely to have a 1st, 2nd, or 3rd degree relative also diagnosed with CFS. The data examined was a patient registry in Utah that utilizes the genealogy compiled by the Mormon church and has been made available to research groups in the state. Number of records examined is huge (records for roughly 200,000 patients were examined - making the results likely to be quite stable). The bottom line was that the "Relative risks for first (RR = 2.70), second (RR = 2.34), and third degree (RR = 1.93) relatives were significantly elevated." That the RR is almost two for third degree relatives suggests that the increased risk for CFS is more than just environmental. Again, the study was suggestive and the Dx criteria was nearly non-existent but they were trying to find a cause, they were just looking to see if there were hints of a genetic component and this suggests that there might be a widespread genetic vulnerability.