The test for this condition looks at antibody titers in the blood against folate receptor alpha. Those receptors are located on the brain, at the interface between the blood and the cerebrospinal fluid, and ensure the transport of folate from the blood to the CSF. If there are antibodies against those receptors, then the transport of folate from the blood to the brain will be impaired. As a result, you will see low levels of folates in the brain, even with normal levels in the blood. The higher the antibody titers, the lower the brain folate levels.
There are several negative consequences of low folate levels in the brain, because folate in one of the basic bricks to make many things: neurotransmitter, methylation, glutathione, detox, etc… As a result some brain functions and central nervous system functions will be impaired, depending on individuals, additional insults, age of onset, etc… So obviously the relevance to autism is that cerebral folate deficiency causes brain dysfunction, so could be responsible for part of the autistic symptoms. Also, the doctors who’ve been treating hundreds of patients for this condition for over a year now (Rossignol’s practice and Scott Smith’s), say about 75% of children with autism have it, as well as many parents.
The good thing is that this is treatable: by giving high doses of oral folates (typically 100 times the RDA), one can reach a high enough level of folate in the blood (higher than normal) so that enough folates can cross the BBB even with folate receptors blocked by the antibodies. Another key element of the treatment is a dairy-free diet (no milk, yogurt, cheese, whey, colostrum, butter, ghee, etc…), because dairy products from any mammals (humans included) include a folate binding protein that is very close to the folate receptor alpha and thus flares the autoimmune response. So a dairy free diet allows to decrease the titers, and high doses of oral folates allows brain folate levels to be restored.
The main problem is depending on individual weaknesses in metabolism, some have trouble handling all this extra folate circulating through the body.