MTHFR and other methylation mutations

According to Dr. David Kaufman of Open Medicine Institute, diagnostic markers for ME/CFS include low natural killer cell function, low vasopressin levels, mutations of the MTHFR gene, and abnormalities of the HPA axis:

http://www.nytimes.com/2015/02/25/opinion/understanding-chronic-fatigue.html?_r=1

Note that by this definition, the infectious agent involved does not define the disease; indeed many people have many reactivated pathogens only revealed upon careful and reliable testing, including, herpes viruses, parvovirus, lyme, babesia, bartonella, etc.