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$Unique_ID{BRK04259}
$Pretitle{}
$Title{Tetrahydrobiopterin Deficiency}
$Subject{Tetrahydrobiopterin Deficiency Atypical Hyperphenylalaninemia
Malignant Hyperphenylalaninemia BH4 Deficiency Dihydrobiopterin Synthetase
(DHBS) Deficiency Dihydropteridine Reductase (DHPR) Deficiency Guanosine
Triphosphate-Cyclohydrolase Deficiency Hyperphenylalaninemia Phenylketonuria
(PKU)}
$Volume{}
$Log{}
Copyright (C) 1987, 1990 National Organization for Rare Disorders, Inc.
438:
Tetrahydrobiopterin Deficiency
** IMPORTANT **
It is possible the main title of the article (Tetrahydrobiopterin
Deficiencies) is not the name you expected. Please check the SYNONYMS
listing on the next page to find alternate names, disorder subdivisions, and
related disorders covered by this article.
Synonyms
Atypical Hyperphenylalaninemia
Malignant Hyperphenylalaninemia
BH4 Deficiency
DISORDER SUBDIVISIONS
Dihydrobiopterin Synthetase (DHBS) Deficiency
Dihydropteridine Reductase (DHPR) Deficiency
Guanosine Triphosphate-Cyclohydrolase Deficiency
Information on the following diseases can be found in the Related
Disorders section of this report:
Hyperphenylalaninemia
Phenylketonuria (PKU)
General Discussion
** REMINDER **
The information contained in the Rare Disease Database is provided for
educational purposes only. It should not be used for diagnostic or treatment
purposes. If you wish to obtain more information about this disorder, please
contact your personal physician and/or the agencies listed in the "Resources
section of this report.
Tetrahydrobiopterin Deficiency is a rare genetic, neurological disorder
present at birth. It is caused by an inborn error of metabolism.
Tetrahydrobiopterin is a natural substance (coenzyme) that enhances the
action of enzymes. When Tetrahydrobiopterin is deficient, an abnormally
high blood level of the amino acid phenylalanine occurs and low levels of
some neurotransmitters are found. To avoid irreversible neurological damage,
diagnosis and treatment of this progressive disorder are essential early in
life.
Symptoms
In general, symptoms of Tetrahydrobiopterin Deficiency usually include
neurological problems, muscle tone and coordination abnormalities, seizures,
and delayed motor development.
When enzymes including dihydrobiopterin synthetase, guanosine
triphosphate-cyclohydrolase or dihydropteridine reductase are deficient,
abnormal metabolism of tetrahydrobiopterin (a coenzyme necessary for enzyme
metabolism) occurs. Tetrahydrobiopterin is required for the proper activity
of three enzymes. When it is deficient, high blood levels of the amino acid
phenylalanine can occur, and low levels of brain neurotransmitters will be
found. Elevation levels of phenylalanine may range from mild too severe.
However, symptoms are unresponsive to a phenylalanine-restricted diet because
of the deficiency of brain chemicals that transmit signals. In time,
irreversible mental retardation will occur in the absence of appropriate
treatment. Treatment of tetrahydrobiopterin deficiency can include
replacement therapy with tetrahydrobiopterin and/or neurotransmitter
precursors.
Causes
Tetrahydrobiopterin Deficiency are inherited as autosomal recessive traits.
(Human traits including the classic genetic diseases, are the product of the
interaction of two genes for that condition, one received from the father and
one from the mother. In recessive disorders, the condition does not appear
unless a person inherits the same defective gene from each parent. If one
receives one normal gene and one gene for the disease, the person will be a
carrier for the disease, but usually will show no symptoms. The risk of
transmitting the disease to the children of a couple, both of whom are
carriers for a recessive disorder, is twenty-five percent. Fifty percent of
their children will be carriers, but healthy as described above. Twenty-five
percent of their children will receive both normal genes, one from each
parent and will be genetically normal.)
Symptoms develop due to lack of enzyme activity leading to high blood
levels of the amino acid phenylalanine and low levels of neurotransmitter
chemicals which can cause brain damage.
Affected Population
Tetrahydrobiopterin Deficiency occurs worldwide and is estimated to affect
one to three percent of infants diagnosed with high levels of the amino acid
phenylalanine at birth. Phenylketonuria (PKU) occurs at a rate of 1 in 10 to
20 thousand live births in the United States. Tetrahydrobiopterin deficiency
is very rare with less than 20 known patients identified in North America.
Related Disorders
Symptoms of the following disorders can be similar to those of
Tetrahydrobiopterin Deficiency. Comparisons may be useful for a differential
diagnosis:
Hyperphenylalaninemia is identified by the presence of abnormally high
blood levels of the amino acid phenylalanine in newborns. It may or may not
be associated with elevated levels of another amino acid, tyrosine, in these
children. This disorder may be a symptom of Phenylketonuria (PKU) or it can
be linked with short term deficiencies of either phenylalanine hydroxylase or
p-hydroxyphenylpyruvic acid oxidase.
Phenylketonuria (PKU) is a hereditary metabolic disorder characterized by
the inability to metabolize the amino acid phenylalanine. Uncontrolled
accumulations of phenylalanine in the blood during childhood results in
progressive, severe, irreversible mental retardation. A phenylalanine
restricted diet can prevent brain damage if the disorder is identified early
in infancy. Unlike PKU, a phenylalanine restricted diet does not prevent
brain damage in patients with tetradydrobiopterin deficiency. (For more
information on this disorder, choose "PKU" as your search term in the Rare
Disease Database).
Therapies: Standard
Treatment of Tetrahydrobiopterin Deficiency should be started as early as
possible to avoid progression of complications such as brain damage. A low
phenylalanine diet does not control the metabolic imbalance. However, this
diet may be necessary to keep phenylalanine levels within normal range. As
an alternative to the low phenylalanine diet, low doses of
tetrahydrobiopterin (BH4) may normalize blood phenylalanine levels by
restoring normal liver phenylalanine hydroxylase activity. Genetic
counseling will be of benefit to patients and their families.
Therapies: Investigational
Treatments being tested for Tetrahydrobiopterin Deficiency include
replacement of neurotransmitters such as L-dopa and 5-hydroxytryptophan
administered in conjunction with an inhibitor of amino acid synthesis
(decarboxylation). The long-term effects of high dosage tetrahydrobiopterin
administration have not been established, although this therapy has shown
dynamic improvement in some patients. Synthetic forms of tetrahydrobiopterin
are also under study for use in treating this disorder. The long-term
benefits of these therapies have not yet been established, but clinical
research studies are being conducted to determine appropriate treatment and
effectiveness.
The Food and Drug Administration (FDA) has awarded a research grant to
Joseph Muenzer, M.D., University of Michigan, Ann Arbor, MI, for studies on
Tetrahydrobiopterin as a treatment for this disorder.
For information on additional therapies that have been designated as
Orphan Drugs in the last few months, please return to the main menu of NORD
Services and access the Orphan Drug Database.
This disease entry is based upon medical information available through
March 1990. Since NORD's resources are limited, it is not possible to keep
every entry in the Rare Disease Database completely current and accurate.
Please check with the agencies listed in the Resources section for the most
current information about this disorder.
Resources
For more information on Tetrahydrobiopterin Deficiency, please contact:
National Organization for Rare Disorders (NORD)
P.O. Box 8923
New Fairfield, CT 06812-1783
(203) 746-6518
NIH/National Institute of Neurological Disorders & Stroke (NINDS)
9000 Rockville Pike
Bethesda, MD 20892
(301) 496-5751
(800) 352-9424
National Association for Retarded Citizens of the U.S.
P.O. Box 6109
Arlington, TX 76005
(817) 640-0204
1-800-433-5255
National Institute on Mental Retardation
York University
Kinsmen MIMR Building
4700 Keele Street, Downview
Toronto, Ont. M3J 1P3
Canada
(416) 661-9611
Children's Brain Disease Foundation for Research
350 Parnassus, Suite 900
San Francisco, CA 94117
(415) 565-6259
(415) 566-5402
Research Trust for Metabolic Diseases in Children
Golden Gates Lodge, Weston Rd.
Crewe CW1 1XN, England
Telephone: (0270) 250244
For information on genetics and genetic counseling referrals, please
contact:
March of Dimes Birth Defects Foundation
1275 Mamaroneck Avenue
White Plains, NY 10605
(914) 428-7100
Alliance of Genetic Support Groups
35 Wisconsin Circle, Suite 440
Chevy Chase, MD 20815
(800) 336-GENE
(301) 652-5553
References
HYPERPHENYLALANINAEMIA DUE TO IMPAIRED DIHYDROBIOPTERIN BIOSYNTHESIS:
LEUKOCYTE FUNCTION AND EFFECT OF TETRAHYDROBIOPTERIN THERAPY: K. Fukuda, et
al.; J Inherited Metab Dis (1985, issue 8(2)). Pp. 49-52.
HYPERPHENYLALANINAEMIA CAUSED BY DEFECTS IN BIOPTERIN METABOLISM: S.
Kaufman; J Inherited Metab Dis (1985, issue Suppl 1). Pp. 20-27.
DIFFERENTIAL DIAGNOSIS OF TETRAHYDROBIOPTERIN DEFICIENCY: A.
Neiderweiser, et al.; J Inherited Metab Dis (1985, issue 8 Suppl 1). Pp. 34-
38.