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$Unique_ID{BRK03415}
$Pretitle{}
$Title{Acidemia, Methylmalonic}
$Subject{Acidemia, Methylmalonic Methylmalonic Acidurias Ketotic
Hyperglycinemia Propionic Acidemia}
$Volume{}
$Log{}
Copyright (C) 1987, 1988, 1990 National Organization for Rare Disorders,
Inc.
427:
Acidemia, Methylmalonic
** IMPORTANT **
It is possible the main title of the article (Methylmalonic Acidemias is
not the name you expected. Please check the SYNONYMS listing on the next
page to find alternate names and disorder subdivisions covered by this
article.
Synonyms
Methylmalonic Acidurias
Information on the following diseases can be found in the Related
Disorders section of this report:
Ketotic Hyperglycinemia
Propionic Acidemia
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.
Methylmalonic Acidemias are one type of organic acidemia. All known
organic acidemias are inherited as autosomal recessive traits. They are
caused by an enzymatic defect in the metabolism of one amino acid. This
results in an abnormally high level of acid in the blood and body tissues and
concomitant metabolic acidosis. Acutely, drowsiness, coma, and seizures may
occur. Mental retardation is a long-term consequence. The disorders may be
caused either by a deficiency of the enzyme methylmalonyl CoA mutase,
methylmalonyl racemase, or of adenosylcobalamin synthetic enzymes. Excretion
of methylmalonate, a product of amino acid metabolism, in the urine is
abnormally high.
Symptoms
The onset of the Methylmalonic Acidemias usually occurs during the first few
months of life. Symptoms may include lethargy, failure to thrive, recurrent
vomiting, acidosis, dehydration, respiratory distress, diminished muscle
tone, developmental retardation, seizures and/or an enlarged liver.
Laboratory findings include an abnormally high amount of methylmalonic
acid in the blood and urine. Metabolic acidosis also occurs. Elevated
levels of ketone bodies such as acetone in the blood (ketonemia) or in the
urine (ketonuria) may develop. An elevated level of ammonia in the blood
(hyperammonemia) may also be present. Excessive levels of the amino acid
glycine in the blood (hyperglycinemia) and in the urine (hyperglycinuria) is
found. The concentration of white blood cells, blood platelets and red blood
cells may be lower than normal. Low blood sugar (hypoglycemia) may also
occur.
Causes
The Methylmalonic Acidemias 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.)
Related Disorders
Symptoms of the following disorders are similar to those of Methylmalonic
Acidemias. Comparisons may be useful for a differential diagnosis.
Ketotic Hyperglycinemia is a group of hereditary protein metabolism
disorders. In each case, a defective enzyme prevents the breakdown of
certain amino acids and lipids. High levels of the amino acid glycine and
ketones accumulate in the blood and urine. Clinically, affected infants have
feeding difficulties and developmental, neurological, digestive, and
metabolic problems, as well as increased susceptibility to infections.
Often, complications can be avoided with early treatment. The disorders are
very rare, with only a few individual cases reported. Methylmalonic Acidemia
is a form of Ketotic Hyperglycinemia. (For more information on this
disorder, choose "Ketotic Hyperglycinemia" as your search term in the Rare
Disease Database.)
Propionic Acidemia is a very rare genetic form of Ketotic
Hyperglycinemia. This disorder is caused by a deficiency of the enzyme
propionyl CoA carboxylase, one of the enzymes necessary in the process of
breaking down amino acids. (For more information on this disorder, choose
"Propionic Acidemia" as your search term in the Rare Disease Database.)
Affected Population
The Methylmalonic Acidemias occur at a rate of 1 in 50,000 to 1 in 100,000
live births.
Therapies: Standard
The diet of children with Methylmalonic Acidemias must be carefully
controlled. Treatment includes a low-protein diet and avoidance of the
amino acids isoleucine, valine, and threonine. To assure a balanced diet,
certain medical foods must be fed to affected children. Pharmacologic doses
of vitamin B12 are indicated in the B12-responsive variants.
Genetic counseling is recommended for the families of children with
Methylmalonic Acidemias.
Therapies: Investigational
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 Methylmalonic Acidemias, please contact:
National Organization for Rare Disorders (NORD)
P.O. Box 8923
New Fairfield, CT 06812-1783
(203) 746-6518
Organic Acidemia Association
522 Lander St.
Reno, NV 89512
(702) 322-5542
British Organic Acidemia Association
5 Saxon Rd.
Ashford, Middlesex TW15 1QL
England
Research Trust for Metabolic Diseases in Children
Golden Gates Lodge, Weston Rd.
Crewe CW1 1XN, England
Telephone: (0270) 250244
For genetic information 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
CLINICAL HETEROGENEITY IN COBALAMIN C VARIANT OF COMBINED HOMOCYSTINURIA AND
METHYLMALONIC ACIDURIA: G.A. Mitchell, et al.; Journal Pediatr (March 1986:
issue 108,3). Pp. 410-415.
THE METABOLIC BASIS OF INHERITED DISEASE, 5th ed.: John B. Stanbury, et
al., eds.; McGraw-Hill, 1983. Pp. 486-493.