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Vitamins are organic molecules that are present in trace amounts
in the diet and that act as coenzymes (eg, pyridoxine), or coenzyme precursors
(eg, riboflavin and thiamine). Several inborn errors that respond
dramatically to treatment with vitamins are described in the following
sections.
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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.
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Because treatment of these conditions is specific and possibly
lifesaving, it is important that they be thought of and recognized
early in patient evaluation.