Mutations in the GCH1, PCBD1, PTS and QDPR genes directly cause BH4 deficiency. Additionally, mutations of the MTHFR gene (A1298C variant) and DHFR can interfere with the recycling of BH4 and lead to less severe, but still clinifically significant, deficiencies of BH4. anyone test positive for this DHFR snp? p.Asp153Val http://www.research-in-germany.de/n...enital-genetic-defect,sourcePageId=66910.html huh. just checked 23andme and I dont' see it. the german researchers describe it as a point mutation.