Nutritional approaches are available for the management of several different classes of
inborn metabolism errors. In
phenylketonuria (PKU),
phenylalanine is not properly metabolized; and its accumulation leads to
neurologic dysfunction and
metal retardation. Altering the diet to limit
phenylalanine intake led to remarkable improvement in children with PKU. It was later found that instituting dietary
therapy immediately after identification of the disorder in newborns prevented
mental retardation. Throughout the 1960s nutritional
therapies were found for other inborn disorders, including
galactosemia,
maple syrup urine disease, and
homocystinuria. For the group of disorders associated with defects in the
urea cycle, leading to profound
hyperammonemia,
therapy based on the concept of waste
nitrogen excretion (i.e., by increasing excretion of
urea cycle intermediates in the urine,
nitrogen that would otherwise recycle as
ammonia can be eliminated) dramatically produced better control of
hyperammonemia and its consequences. Some
inborn errors of metabolism respond to
vitamin therapy.
Biotin-related multiple carboxylase
synthetase deficiency can be produced by either of two
enzyme defects--
holocarboxylase synthetase deficiency or
biotinidase deficiency. Both are treatable with
biotin supplementation. The symptoms of
multiple carboxylase deficiency can also occur after intestinal resection or ingestion of raw eggs.
Multiple carboxylase deficiency has been treated successfully in utero by giving the mother
biotin supplements.
Peroxisomal disorders may respond to dietary management.
Liver disease in
hereditary tyrosinemia may be accentuated by
hypermethioninemia and treated by controlling the blood
methionine level.
Glycogen storage disease Type I, which causes
hypoglycemia, can be controlled by
oral administration of
cornstarch.