Peer-reviewed article linking MTHFR mutation to smallpox vaccine reactions.
https://www.ncbi.nlm.nih.gov/m/pubmed/18454680/
The data demonstrate that 677C T polymorphisms, whether homozygous or heterozygous, are significantly associated with ASD. Those with two copies of the MTHFR 677C mutation had a 50% decrease in enzymatic activity while those with only one copy had a 30% decrease. The data support the hypothesis that ASD syndromes are associated with single nucleotide mutations of the MTHFR gene in some cases. Notably, only 2% of children with ASD in our study presented without at least one polymorphism in the MTHFR gene.
http://jpands.org/vol9no4/boris.pdf
Genetics Home Reference: MTHFR
https://ghr.nlm.nih.gov/gene/MTHFR
MTHFR Polymorphism, Homocysteine and Cardiovascular Disease
http://www.ncbi.nlm.nih.gov/pubmed/11683544
MTHFR and Neural Tube Defects
http://www.bmj.com/content/328/7455/1535
Cardiovascular Disease
http://www.ncbi.nlm.nih.gov/pubmed/22492374