Intunejune: "Primary immune deficiencies are also "in the genes." I too agree that a large subset of CFIDS people have genetic issues esp. with their immune system (Mitochondria damage/dysregulation). All i have to do is to look back to my father, his mother, his brother, and the odd tales of previous generations and I can not help but believe there is a rather large component to CFIDS. Now, not all people who get CFIDS will have that genetic damage right out out of the womb - like my husband who must have gotten the virus/pathogen from living with me for 10 years and then got sick for the next 6 years - I have been sick 16 years. I would bet that another subgroup acquires this virus (or other viruses) from contact since apparently XMRV is highly contagious but has a long incubation period. That would make sense with my husband and living with me for ten years, immense stress that damaged his immune system, a virus of some sort, and bang, down he went and has not gotten back up in six years. Dr. Jonathan Kerr identified those genes that were up and down -regulated.