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$Title{Forbes Disease}
$Subject{Forbes Disease Amylo-1,6-Glucosidase Deficiency Cori Disease
Debrancher Deficiency Glycogen Storage Disease III Glycogenosis Type III Limit
Dextrinosis Von Gierke Disease Andersen Disease Hers Disease Glycogen Storage
Disease VIII}
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Copyright (C) 1987, 1990, 1991 National Organization for Rare Disorders,
Inc.

396:
Forbes Disease

** IMPORTANT **
It is possible the main title of the article (Forbes Disease) 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

     Amylo-1,6-Glucosidase Deficiency
     Cori Disease
     Debrancher Deficiency
     Glycogen Storage Disease III
     Glycogenosis Type III
     Limit Dextrinosis

Information on the following diseases can be found in the Related
Disorders section of this report:

     Von Gierke Disease
     Andersen Disease
     Hers Disease
     Glycogen Storage Disease VIII

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.


Forbes Disease is a glycogen storage disorder inherited through autosomal
recessive genes.  Symptoms are caused by a lack of the enzyme amylo-1,6
glucosidase (debrancher enzyme).  This enzyme deficiency causes excess
amounts of glycogen (the stored form of energy that comes from carbohydrates)
to be deposited in the liver, muscles and heart.  The heart may be involved
in some cases.

Symptoms

Symptoms of Forbes Disease during the first 4 to 6 years of life may be
indistinguishable from Von Gierke Disease.  The amounts of glycogen in the
liver and muscles is abnormally high.  The liver is enlarged and the abdomen
protrudes.  The muscles tend to be flaccid.

A child with Forbes Disease has a short stature, low blood sugar
(hypoglycemia) that does not respond to the hormone glucagon, and an elevated
level of fatty substances in the blood, known as hyperlipemia.  Patients with
Forbes Disease may also have difficulty fighting infections, and may
experience unusually frequent nosebleeds.

Some individuals may have virtually no other symptoms of Forbes Disease
other than a protruding abdomen and an enlarged liver.  These patients tend
to lose these few symptoms during adolescence when their liver decreases
progressively in size.  Children with Forbes Disease often grow slowly during
childhood and puberty may be delayed, but their adult height is usually
normal.

Causes

Forbes Disease is a disorder inherited through autosomal recessive genes.
The disorder is caused by lack of a debrancher enzyme (amylo-1,6-glucosidase)
which is involved in the formation of the stored form of carbohydrates
(glycogen).  Glycogen is stored in the liver and muscles for future energy
needs when it is converted into sugar (glucose).  Glucose is used as a
readily available source of energy.  Without the debrancher enzyme, glycogen
can only be broken down partially and the structure that is left, resembling
a molecule called a "limit dextrin", may accumulate in liver and muscle
tissues.

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.

Affected Population

All Glycogen Storage Diseases together affect less than 1 in 40,000 persons
in the United States.  Forbes Disease usually begins during childhood.  It
affects males as often as females.  Patients with this disorder reported in
Israel were generally of North African heritage.

Related Disorders

Glycogen Storage Diseases involve inborn errors of metabolism in which the
balance between stored energy (glycogen), and available energy (sugar or
glucose), is disturbed.  Too much glycogen tends to be stored in the liver
and muscles, and too little sugar is available in the blood.

The following diseases are similar to Forbes Disease.  These can be
compared with Forbes Disease for a differential diagnosis:

Von Gierke Disease is a more severe form of glycogen storage disease.  It
is a hereditary metabolic disorder caused by an inborn lack of either the
enzyme glucose-6-phosphatase or the enzyme glucose-6-phosphate translocase.
These enzymes are needed to convert the main carbohydrate storage material
(glycogen) into sugar (glucose) which the body uses for its energy needs.  A
deficiency of these enzymes causes abnormal deposits of glycogen in the liver
and kidney cells.

Andersen Disease is a glycogen storage disease inherited through
recessive genes.  Symptoms of this disorder are caused by a lack of a
brancher enzyme amylo transglucosidase.  The lack of this enzyme causes an
abnormality in the structure of the main carbohydrate storage material
(glycogen).  Andersen Disease is characterized by scarring of the liver
(cirrhosis) which may lead to liver failure.

Hers Disease is a mild genetic form of glycogen storage disease.  The
disorder is caused by a deficiency of the enzyme liver phosphorylase.  Hers
Disease is characterized by enlargement of the liver (hepatomegaly),
moderately low blood sugar (hypoglycemia), elevated levels of acetone and
other ketone bodies in the blood (ketosis), and moderate growth retardation.
Symptoms are not always evident during childhood.  Children are able to lead
normal lives.  In other cases, severe symptoms may be present.

Glycogen Storage Disease VIII is a sex-linked genetic disorder caused by
a deficiency of the enzyme liver phosphorylase kinase.  The disorder is
characterized by slightly low blood sugar (hypoglycemia).  Excess amounts of
glycogen (the stored form of energy that comes from carbohydrates) are
deposited in the liver, causing enlargement of the liver (hepatomegaly).

For more information on the above disorders, choose "Von Gierke,"
"Andersen," "Hers," and "Glycogen Storage VIII" as your search terms in the
Rare Disease Database.

Therapies:  Standard

Diagnosis of Forbes Disease may be confirmed by tests for the presence of
glycogen and the debrancher enzyme in muscle and liver biopsies.  White blood
cells and connective tissue cells called fibroblasts can also be useful for
similar diagnostic tests.

Treatment of Forbes Disease is aimed at prevention of low blood sugar
(hypoglycemia).  Frequent small servings of carbohydrates and a high protein
diet are advised during the day.  At night continuous tube feeding of food
solutions such as Vivonex or polycose (glucose) may be administered to
promote normal childhood growth.

Genetic counseling is helpful for families of children with Forbes
Disease and other Glycogen Storage Diseases.  People with this disorder can
expect to live a normal life span.  However, muscle disorders may develop
with age.

Therapies:  Investigational

Dr. Y.T. Chen at Duke University Medical Center, at the request of the
Glycogen Storage Disease Association, is collecting DNA from patients with
Glycogen Storage Disease Type I to form a DNA bank for GSDI.  Interested
patients may contact the Glycogen Storage Diseases Association for further
information.  The address and phone number of the organization are listed in
the Resources section of this report.

This disease entry is based upon medical information available through
February 1991.  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 Forbes Disease, please contact:

     National Organization for Rare Disorders (NORD)
     P.O. Box 8923
     New Fairfield, CT  06812-1783
     [phone]

     Association for Glycogen Storage Diseases
     Box 896
     Durant, IA  52747
     [phone]

     National Digestive Diseases Information Clearinghouse
     Box NDDIC
     Bethesda, MD  20892
     [phone]

     Research Trust for Metabolic Diseases in Children
     Golden Gates Lodge, Weston Rd.
     Crewe CW1 1XN, England
     Telephone:  [phone]

For information on genetics and genetic counseling referrals, please
contact:

     March of Dimes Birth Defects Foundation
     1275 Mamaroneck Avenue
     White Plains, NY  10605
     [phone]

     Alliance of Genetic Support Groups
     35 Wisconsin Circle, Suite 440
     Chevy Chase, MD  20815
     (800) 336-GENE
     [phone]

References

MYOPATHY AND GROWTH FAILURE IN DEBRANCHER ENZYME DEFICIENCY:  IMPROVEMENT
WITH HIGH-PROTEIN NOCTURNAL ENTERAL THERAPY:  A.E. Slonim, et al.; Journal
of Pediatrics (December 1984:  issue 105,6).  Pp. 906-911.

NEUROMUSCULAR INVOLVEMENT IN GLYCOGEN STORAGE DISEASE TYPE III:  S.W.
Moses, et al.; Acta Paediatrica Scandinavica (March 1986:  issue 75,2).  Pp.
289-296.