902
chapter 38
Vitamin Metabolism
TA B LE 38-1
Genetic Disorders That Respond Favorably to Treatment with Pharmacological Doses of Vitamins*
Therapeutic Vitamin
Daily Dose
Disorder*
Biochemical/Biological Defect
Vitamin D
(adult RDA =
>
1 0 0 , 0 0 0
units
Familial X-linked
hypophosphatémie rickets*
Unknown
200IU = 50 jug of
>25,000 units
Vitamin D-dependent
Defect in
cholecalciferol)
rickets, type I
25 -(OH)D-1 -ct-hydroxy lase
Ascorbic acid
(vitamin C; adult
RDA = 60 mg)
4g
Ehlers-Danlos syndrome,
type VI (ocular type)
Procollagen lysyl hydroxylase
Biotin
1 0
g
Multiple carboxylase
Holocarboxylase synthetase, or
(RDA has not
been established)
deficiency*
defect in intestinal or cellular
uptake, or intracellular
transport
1 0
mg
Propionic acidemia;
ketoacidosis
Propionyl-CoA carboxylase
Cobalamin
<5Mg
Megaloblastic anemia
Decreased intestinal absorption
(vitamin B)2; adult
RDA = 3.0 Rg)
(juvenile pernicious anemia)
due to abnormality of intrinsic
factor or ileal mucosal cells,
or absence of intrinsic factor
> 1 0 0
Mg
Megaloblastic anemia
Transcobalamin II
>250 Mg
Methylmalonic aciduria;
ketoacidosis
Adenosyl cobalamin formation
>500 Mg
Methylmalonic aciduria;
homocystinuria
Formation of both adenosyl
and methyl cobalamins
Folic acid
> 1 0
mg
Megaloblastic anemia
Defect in intestinal and perhaps
(folacin; adult
and mental retardation*
brain transport of folate
RDA = 400 Mg)
> 1 0
mg
Homocystinuria and
hypomethioninemia
N5, N
1
¬į-Methy lenetetrahydrofolate
reductase
>5 mg
Formiminoglutamic aciduria
and mental retardation
Probably formiminotransferase
Lipoic acid
3-10 mg
Lactic and pyruvic acidemia
11
Pyruvate carboxylase
Niacin
(adult RDA =
13 mg = 13
niacin equiv.)
50-250 mg
Hartnup disease
Intestinal and renal transport
of tryptophan (high protein
diet needed in addition to
niacin to relieve symptoms)
Pyridoxine
10-50 mg
Infantile convulsions
Perhaps glutamate
decarboxylase
[vitamin B6; adult
> 1 0
mg
B6-responsive anemia
*11
Unknown
RDA = 2.2 mg
>25 mg
Cystathioninuria
y-Cystathionase
(men),
2 . 0
mg
5-10 mg
Homocystinuria
Cystathionine synthetase
(women)]
>
1 0 0
mg
Primary hyperoxaluria,
type I
Soluble glyoxalate,
a-ketoglutarate carboligase
5-10 mg
Xanthurenic aciduria*
Kynureninase
18-30 mg
Gyrate atrophy of
choroid and retina;
hyperomithinemia
Ornithine: 2-oxoacid
aminotransferase
(continued)
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