CFS involves a large variety of symptoms (71,72), the chief ones being extreme fatigue, post-exertional malaise and/or fatigue, sleep dysfunction, muscle pain, and symptoms involving the brain that are significant but less profound than in autism (e.g. cognitive and memory difficulties).
The author proposes that these differences result at least in part from the different ages at onset. Autism develops early in life, before the brain is completely developed and before puberty, while the onset of CFS occurs after brain development is completed and (for the most part) after puberty.
Pangborn (73) has discussed five hypotheses that have been suggested to explain the higher prevalence of autism in boys. Of these, the one that appears to be most consistent with the present author’s hypothesis of a common pathogenesis between CFS and autism is the one put forward by Geier and Geier (74). Their hypothesis proposes that the higher prevalence of autism in boys results from the potentiation of mercury toxicity by testosterone, while estrogen is protective. There is increasing evidence that mercury was a significant factor in the etiology of many cases of autism, because mercury-containing thimerosol was used as a preservative in vaccines given to them. Since thimerosol was removed from childhood vaccines, the number of new cases of neurodevelopmental disorders, including autism, has been found to be dropping (75).
The present author has proposed a hypothesis (76) to explain the higher prevalence of CFS in women, involving an additional bias toward oxidative stress due to redox cycling in the metabolism of estradiol when certain polymorphisms are present.
With regard to symptoms, it seems likely that the role of methylation in the formation of myelin basic protein (77) is at least part of the explanation for the major problems in brain development in autism and the symptoms that result from them.
Fatigue is not recognized to be a major feature of autism. However, it should be noted that the evaluation of fatigue is usually based on self-report, which is not possible in children who are unable to speak. Also, it seems possible that fatigue may be manifested differently in very young children as compared with adults. Features such as hyperactivity and irritability may reflect fatigue in these patients.
Chronic pain may also be difficult to identify and characterize in children who do not have speech. A recent paper suggests that chronic pain may be the initial presenting symptom in cases of undiagnosed autism (78).
Many of the other phenomena found in CFS are also found in autism, but historically they have not received as much attention in autism as the brain-related symptoms, perhaps because the latter are so striking and profound. Some of the other phenomena that autism has in common with CFS in addition to those already mentioned are elevated proinflammatory cytokines (79), Th2 shift in the immune response (80), low natural killer cell activity (81), mitochondrial dysfunction (82, 83), carnitine deficiency (83), hypothalamus-pituitary-adrenal (HPA) axis dysfunction (84), gut problems (85), and sleep problems (86).