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Library of Medicine®| Glycogen storage disease type IV On this
page: Reviewed February 2013 What is glycogen storage disease
type IV? Glycogen storage disease type IV (GSD IV) is an
inherited disorder caused by the buildup of a complex sugar
called glycogen in the body's cells. The accumulated glycogen is
structurally abnormal and impairs the function of certain organs
and tissues, especially the liver and muscles. There are five
types of GSD IV, which are distinguished by their severity,
signs, and symptoms. The fatal perinatal neuromuscular type is
the most severe form of GSD IV, with signs developing before
birth. Excess fluid may build up around the fetus
(polyhydramnios) and in the fetus' body. Affected fetuses have a
condition called fetal akinesia deformation sequence, which
causes a decrease in fetal movement and can lead to joint
stiffness (arthrogryposis) after birth. Infants with the fatal
perinatal neuromuscular type of GSD IV have very low