The mechanisms that underlie how different conditions respond
to vitamins are quite varied. Some mutations reduce absorption of
a vitamin(s) across the intestinal mucosa, others limit transport
between the gut and other tissues, and yet others impair their incorporation into
coenzymes (eg, vitamin B12 into adenosyl- and methyl-B12)
or holoenzymes (eg, biotin into holocarboxylases). Mutations in catalytic
proteins may reduce their interactions with their coenzymes, and
in pyridoxine-dependant seizures, an accumulated compound binds
pyridoxine and makes it unavailable as a coenzyme. In yet other
cases, as in biotin-responsive basal ganglia disease, the mechanism
of vitamin responsiveness is unknown.