Duncan,Would metabolites be able to tell us anything if the problem lies in the nervous system?
Absolutely. For example, all your neurotransmitters and neuro-peptides are created by your metabolism. So are many closely related molecules essential to the nervous system. All of the signaling molecules in the immune system are also. There is a nice Sigma Aldrich Chart that shows a simplified diagram of your metabolic pathways. This simplified diagram of the human metabolic system can give you a quick sense as to the complexity but also how almost every system in your body is dependent on its correctly functioning.
http://www.sigmaaldrich.com/content/dam ... poster.pdf
You can take a closeup look here:
http://www.sigmaaldrich.com/technical-d ... s-map.html
If you scan the various pathways you will quickly notice virtually all the molecules that are needed for your central and peripheral nervous systems to function are created by either DNA expression or your metabolism and rely on a correctly functioning metabolism. One excellent way of "looking" at the metabolic process is simply analyzing all the metabolites in your various biological samples like blood or urine. So if there is some problem in the pathways that synthesize these molecules, it will probably show up as an irregularity in some of the the metabolites. You can think of that as a signature. Statistics can be used to eliminate noise and extract meaningful patterns.
I was told that this current technology UCSD is using is able to identify over 800 metabolites and their levels and that the target is about 2000. Your metabolism is the vastly complex but is a fairly tightly regulated process of breaking down the food you eat into all the molecules every part of your body needs to operate in conjunction with molecules produced through DNA expression. So a combination of your DNA, how its being expressed, what your body is taking in and is storing plus the current state of your metabolic system runs your entire body. So a problem with any of these can disrupt you in any number of ways including neurologically.
The beauty of this approach is it "sees" through the noise created by the complex DNA master control and differences between people so long as the cohort studied is "similar". For example, men and women have important differences and should be studied separately. By looking using the right statistical filtering at the intermediate through end product metabolites, one gets a a view of the metabolism one cannot get any other way. So yes, its probably one of the best approaches to look for "why" someone is experiencing chronic symptoms since those symptoms have a good chance of being represented by a metabolic signature that is not normal and reflects on certain pathways somehow involved in the proper functioning of the nervous system.
If you look around, there has been an endless series of papers about the power of metabolomics in studying neurological diseases. Here is a few but I did not review them.... just examples
If you go to Pubmed or Google Scholar and search on "metabolomics central nervous system" or something similar, you will find many papers where its being used to explore this.
http://www.nature.com/npp/journal/v34/n ... 8174a.html
http://masspec.scripps.edu/publications ... 44_art.pdf