Wow, this is potentially an incredibly important study: though the standard proviso about replication applies, especially for such a small study.
As far as I know it's the first study to develop an 'in vitro' (lab bench) study that isn't just looking at individual cells taken from the body but
grows functioning muscle cells outside the body. Critically, these are new cells grow away from any factors like autoantibodies, autonomic problems such as blood flow, cytokines or even faulty illness beliefs, and still they find a difference. As others have said that throws up challenges to other models of mecfs if these results are replicated.
Certainly it's the strongest evidence to date of a primary problem in muscles (or in cells at any rate since we don't know the situation tissues other than muscle).
Even more fascinating, the researchers highlight a problem the AMP-Kinase, a key sensor and regulator of the eneryg level of the cell, which is a plausible molecule to have a key role in this illness. As
@nandixon says, AMP-K is active in other tissues, including the brain (they study doens't look at other tissues for comparison) and problems with AMP-K in the brain could explain problems with mental fatigue too. Interestingly, the finding of reduced IL-6 production by the muscle cells from CFS patients ties in with the low AMPK activation as
IL-6 is an AMPK activator.
The big question is how an effect in the body transfers to an effect in cell culture. The study suggests genetics though presumably all the patients were healthy before they got mecfs so the genes they were born with were presumably ok. Epigenetics (long-term, inheritable changes in gene activation) is one mechansim, though presumably infection is another.
This looks to me like it could be an incredibly fruitful area of research and I hope others will try to replicate pronto.
I wonder why they didn't also consider stochastic (autoimmunity) in addition to genetic/epigenetic.
Presumably because autoantibodies couldn't explain defects in the cultured muscles, where the muscles were grown away from the influence of autoantibodies?