Webster's New World Medical Dictionary

glycogen storage disease
One of the multiple
inherited disorders of metabolism that interfere
with glycogen synthesis or breakdown, leading to
the storage of carbohydrates as glycogen in the
body. The conditions may affect the liver or the
skeletal (striated) muscle, both primary glycogen
storage sites. Symptoms and signs depend upon the
exact type but can include enlargement of the liver
(hepatomegaly), hypoglycemia, and muscle weak-
ness or cramps eventually accompanied by muscle
wasting. McArdle disease (glycogen storage disease
type V) is the most common type of glycogen stor-
age disease. McArdle disease is an autosomal reces-
sive disorder caused by mutations in the gene that
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encodes myophosphorylase, an enzyme that is
essential for glycogenolysis. Other types of glycogen
storage disease include von Gierke disease and
Pompe disease.
glycosaminoglycan
A negatively charged chain
of polysaccharides (modified sugars) that is com-
posed of repeating disaccharide units. Abbreviated
GAG. Important GAGs in the human body include
chondroitin sulfate, dermatan sulfate, heparan sul-
fate, heparin, hyaluronate, and keratan sulfate.
GAGs are involved as lubricants and components of
bone, cartilage, blood vessels, and certain types of
cells. Also known as mucopolysaccharides.
GM1-gangliosidosis
A rare genetic lipid storage
disorder that is similar to Hurler syndrome and Tay-
Sachs disease but that affects both the brain and the
viscera. Symptoms include skeletal deformities and
severe effects on the brain and organs. The mutation
that is responsible for the disease is located on
chromosome 3. There is no treatment for GM1-gan-
gliosidosis. Also known as familial neurovisceral
lipidosis and Landing disease. See also 
Hurler syn-
drome; sphingolipidosis; Tay-Sachs disease.