Taking into consideration that in the one-carbon metabolism cystathionine beta-synthase (CBS) catalyzes Hcy in an irreversible way, and that CBS gene is located in chromosome 21, fetuses and infants with DS have functional folate deficiency due to overexpression of CBS.
Among the IBD patients the only independent factor significantly associated with hyperhomocysteinemia was folate deficiency (p = 0.0002), regardless of the MTHFR or the CBS genotype.