51
myopathy, exercise intolerance, and cirrhosis. Death can occur in early childhood
[10, 46].
GSD Type V
It is, also known as McArdle disease, the most common skeletal muscle disorder
[46]. It is an autosomal recessive disorder that is caused by a deficiency in enzyme
myophosphorylase (muscles phosphorylase). This enzyme liberates glucose in skeletal muscles from glycogen [47]. In this disease, muscles are unable to use glycogen
during the physical activity in the initial phase. At the later phase, due to increased
blood supply patients can function normally, this is termed as “second wind” phenomenon [10]. Exercise intolerance which includes myalgia, muscle contractures,
painful cramps, premature fatigue and myoglobinuria is its clinical presentation.
GSD Type VI
It is, also known as hers disease, a very rare disorder caused by a deficiency of liver
phosphorylase which is required for glycogenolysis [40]. Hepatomegaly is the only
clinical symptom [36]. It occurs due to mutation in the PGYL gene [10].
GSD Type VII
It is, also known as Tarui disease, due to deficiency of phosphofructokinase. Exercise
intolerance, myopathy, muscle cramps, hemolysis, hyperuricemia, and myoglobinuria are its clinical presentations [46]. It is clinically similar to GSD type V [10].
GSD Type VIII
This disorder, the mildest form of GSDs, is caused by a phosphorylase enzyme
deficiency which is required for the hydrolysis of glycosidic linkages α1-4 and
α1-6. This results in an accumulation of glycogen in the liver [48]. Hepatomegaly
and CNS degeneration in early childhood are common symptoms. This disorder
shows no hypoglycemia and is fatal in childhood [36].
GSD Type IX
This disorder is caused by a deficiency of phosphorylase kinase enzyme. It has two
subtypes, type IXa which is an autosomal recessive trait and type IXb which is a sexlinked recessive trait. There is no hypoglycemia in this disorder [36]. Hepatomegaly
and fasting ketosis are its clinical presentations [10]. When hepatomegaly occurs in
2 Impaired Carbohydrate Metabolism in Metabolic Disorders
myopathy, exercise intolerance, and cirrhosis. Death can occur in early childhood
[10, 46].
GSD Type V
It is, also known as McArdle disease, the most common skeletal muscle disorder
[46]. It is an autosomal recessive disorder that is caused by a deficiency in enzyme
myophosphorylase (muscles phosphorylase). This enzyme liberates glucose in skeletal muscles from glycogen [47]. In this disease, muscles are unable to use glycogen
during the physical activity in the initial phase. At the later phase, due to increased
blood supply patients can function normally, this is termed as “second wind” phenomenon [10]. Exercise intolerance which includes myalgia, muscle contractures,
painful cramps, premature fatigue and myoglobinuria is its clinical presentation.
GSD Type VI
It is, also known as hers disease, a very rare disorder caused by a deficiency of liver
phosphorylase which is required for glycogenolysis [40]. Hepatomegaly is the only
clinical symptom [36]. It occurs due to mutation in the PGYL gene [10].
GSD Type VII
It is, also known as Tarui disease, due to deficiency of phosphofructokinase. Exercise
intolerance, myopathy, muscle cramps, hemolysis, hyperuricemia, and myoglobinuria are its clinical presentations [46]. It is clinically similar to GSD type V [10].
GSD Type VIII
This disorder, the mildest form of GSDs, is caused by a phosphorylase enzyme
deficiency which is required for the hydrolysis of glycosidic linkages α1-4 and
α1-6. This results in an accumulation of glycogen in the liver [48]. Hepatomegaly
and CNS degeneration in early childhood are common symptoms. This disorder
shows no hypoglycemia and is fatal in childhood [36].
GSD Type IX
This disorder is caused by a deficiency of phosphorylase kinase enzyme. It has two
subtypes, type IXa which is an autosomal recessive trait and type IXb which is a sexlinked recessive trait. There is no hypoglycemia in this disorder [36]. Hepatomegaly
and fasting ketosis are its clinical presentations [10]. When hepatomegaly occurs in
2 Impaired Carbohydrate Metabolism in Metabolic Disorders