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Glycogen Storage diseases

Background

The term glycogen storage diseases (GSDs) refer to a number of inherited metabolic conditions in which an enzyme deficiency causes accumulation of glycogen. Glycogen is stored in the liver and muscle to provide an energy store for the body between meals (liver) and for muscle contraction (muscle). The release of energy as simple sugars from glycogen occurs as a series of chemical reactions. Each reaction requires an enzyme. The different GSDs may be referred to by a number, by the deficient enzyme or by the name of a doctor or scientist associated with the disease.

Enzyme deficiency

number

Alternative name

Glucose-6-phosphatase

I

von Gierke disease

Alpha 1,4-glucosidase (acid maltase)

II

Pompe disease

Debrancher (amylo-1,6 glucosidase)

III

Cori disease

Brancher

IV

Andersen disease

Muscle phosphorylase

V

McArdle disease

Liver phosphorylase

VI

Hers disease

Phosphofructokinase

VII

Tarui disease

Phosphorylase b kinase

IX

Credits

Medical text written May 2000 by Dr J Walter, Consultant Paediatrician, Willink Biochemical Genetics Unit, Royal Manchester Children's Hospital, Manchester, UK. Last updated January 2013 by Dr Helen Mundy Consultant Metabolic Paediatrician, Evelina Children's Hospital, Guys and St Thomas NHS Foundation Trust.

Although great care has been taken in the compilation and preparation of all entries to ensure accuracy, we cannot accept responsibility for any errors or omissions. Any medical information is provided is for education/information purposes and is not designed to replace medical advice by a qualified medical professional.

This entry is pending review, and certain details may no longer be up to date. Please ring our helpline or email our Rare Conditions Information Officer for more information.

What are the symptoms?

Some GSDs affect the liver (I, IV, VI and IX), some the muscles (V and VII) and some affect both (type III).

Conditions affecting the liver cause liver enlargement with a tendency for low blood sugar. Untreated children with liver GSDs tend to be short; with enlarged abdomens and thin limbs. These problems improve dramatically with treatment. A few may develop problems of liver scarring and very occasionally liver tumours. In GSD I there can also be longer term problems with kidney disease. In GSD I there are 2 subtypes Ia and Ib. People with GSD Ib have an increased risk of infections because of a decrease in a particular type of white blood cell.

Disorders affecting muscle may cause muscle weakness or cramping. Excessive exercise may trigger bouts of muscle inflammation. The heart and respiratory (breathing) muscles may be affected, but not in all types.

All types of GSD are at risk of ostepaenia (decreased bone strength), which increases fracture risk in later life.

Type II GSD (see entry Pompe disease) is a disease of heart and muscle but is very different to the other GSDs.

How is it diagnosed?

It is possible to test for the levels of certain enzymes in a specialist laboratory but this may require a sample of affected tissue (eg liver). It is often more straightforward to look at the genes that provide the genetic blueprint/code to make the enzymes to see if any are faulty (mutated).

How is it treated?

Treatment for GSD varies depending on the type.

Children with liver GSDs require frequent daytime feeding and often overnight continuous tube feeding to prevent low blood sugar and to improve growth. In older children and adults this may be replaced with regular starches that are slow releasers of energy.

Protein supplements may be used in GSD type III. Sometimes medicine is required to help the heart muscle.

In muscle GSDs there is little additional medical therapy. Regular but not excessive exercise is encouraged and occasionally if muscles are very weak additional mobility aids may be required.

The prognosis for patients with a liver GSD is usually good. The tendency to low blood sugar always improves with age although the more severely affected will still require regular treatment even as an adult.

Most patients with a muscle GSD will continue to have a degree of exercise limitation throughout life but will adjust to lead relatively normal lives. Occasionally the muscles may become progressively weaker.

Inheritance patterns and prenatal diagnosis

Inheritance patterns
Autosomal recessive (types I, II, III, IV, V, VII, some IX), and X-linked (some IX).

Prenatal diagnosis
This is usually available if required by looking for the gene fault in a chorionic villus biopsy.

Is there support?

The Association for Glycogen Storage Disease UK 

Tel: 0300 123 2790
Email: via website
www.agsd.org.uk

The Association is a Registered Charity in England and Wales No. 1132271. It provides information and support for individuals and families affected by Glycogen Storage Disease. The Association puts people in contact with each other, and holds conferences and workshops.

Group details last updated December 2014.

Further information, support and advice on glycogen storage diseases is available from Climb (see entry Inherited Metabolic diseases) and the Muscular Dystrophy Campaign (see entry Congenital Muscular Dystrophy).