In this pattern of inheritance females can be carriers for the disorder
but the disorder only affects males. Females carry the 'faulty' gene
for the disorder on one of their two X chromosomes. The harmful effects
of the gene are masked by their 'normal' second X chromosome. However,
as males have one X chromosome and one Y chromosome, if they have the
'faulty' gene then the harmful effects are not masked.
What are the symptoms of glycogen storage disorders?
Some
disorders affect the liver (Types I, IV, VI & IX), some the muscles
(Types V & VII) and some both (Type III). Disorders affecting the
liver lead to liver enlargement and can be associated with a tendency
to a low blood sugar. Those affecting the muscles cause muscle weakness
and sometimes kidney disease.
Glycogen storage disorders are
usually first diagnosed in babies and children. The common features,
particularly for Type I, include:
- Abnormally slow growth which may be detected by your child's health visitor or GP on routine examination.
- Low blood sugar levels which can cause symptoms such as sweating, tremor, drowsiness, confusion and sometimes convulsions.
- An enlarged liver which a doctor may feel when they examine your child's abdomen.
- Noticeably weaker muscles. This can mean that your baby can appear 'floppy' when they are held.
- Obesity.
- Problems with bleeding and blood clotting.
- Kidney problems.
In teenagers and adults, glycogen storage disorders usually
cause fatigue (tiredness), feeling weak when exercising, or the feeling
of aching and weak muscles.
Some glycogen storage disorders,
particularly Type Ib, Ic and Id, can affect your immune system and make
you more susceptible to infections.
Glycogen storage disorder
Type II can affect your heart, muscles, liver, nervous system and blood
vessels. In babies, this can lead to breathing problems, muscle
weakness and abnormal enlargement of the heart. This means that the
heart cannot function normally which can lead to heart failure. In
teenagers and adults, glycogen storage disorder Type II can lead to
muscle weakness in the limbs but also weakness of the muscles that are
used to help your breathing. This can lead to difficulty breathing and
respiratory failure.
How are glycogen storage disorders diagnosed?
Glycogen
storage disorders can run in families. There may already be a history
in your family of a glycogen storage disorder which may mean that your
doctor suggests that you or your child are tested.
If your
doctor suspects that you or your child may have a glycogen storage
disease, they may suggest the following investigations:
Blood tests
These may include testing your
blood sugar levels, which may be low, and also blood tests to look at
your kidneys and liver. A special blood test called creatine kinase can
give your doctor information about whether the glycogen storage
disorder is affecting your muscles.
Other blood tests may include checking your blood count to look for anaemia and a test of your blood clotting.
Scans
An abdominal ultrasound scan can show
if the glycogen storage disorder is causing enlargement of your liver.
This is a painless test. It is the same type of scan that pregnant
women have to look at the baby in the womb. Some gel is spread onto
your abdomen. The ultrasonographer then moves the scanning probe over
the surface of your abdomen. High-frequency sound waves allow them to
produce an image of the inside of your abdomen that they can look at.
Your doctor may also suggest a special ultrasound scan of your heart
called an echocardiogram. This is because certain types of glycogen
storage disorders can cause heart problems.
Biopsy
Your doctor may suggest that they
take a biopsy (a sample of tissue) either from one of your muscles or
from your liver. The tissue sample will be sent to the laboratory for
tests and an examination under the microscope. The levels of glycogen
and fat in the tissue can be measured as well as the levels of enzymes
present. This can help to confirm the type of glycogen storage disorder.
Other tests
Other tests are sometimes carried out depending on the type of glycogen storage disorder that your doctor suspects.
What are the treatment options for glycogen storage disorders?
The
treatment for glycogen storage disorders varies depending on which
disorder you have. With most, the treatment aims are to stabilise your
blood sugar and energy levels within your body. This is normally
achieved by using nutritional supplements such as glucose, either via a
drip into your veins, or via a nasogastric tube (a tube that is passed
through your nose into your stomach). When things become more stable,
supplements can be taken by mouth. A high protein diet is also helpful
in some glycogen storage disorders.
Some people with glycogen
storage disorders who do not respond to nutritional supplements need a
liver transplant. People with glycogen storage disorders affecting
their immune system may need to take regular antibiotics to protect
against infection.
In some glycogen storage disorders, clinical
trials have successfully used treatment involving replacement of the
enzymes that are deficient or not working normally. For example, in
glycogen storage disorder Type II, this treatment has been shown to
help reverse the heart problems and muscle weakness that can occur.
Other
clinical trials are underway that are looking at gene therapy as a
treatment. This is where doctors and scientists aim to cure genetic
diseases by introducing 'normal' genes into patients to overcome the
effects of 'faulty' genes, using techniques of genetic engineering.
What is the outlook (prognosis) for glycogen storage disorders?
The
outlook depends on the type of glycogen storage disorder that you have.
Some glycogen storage disorders have a better outlook than others and
do not affect life expectancy. However, some glycogen storage disorders
are more severe and because of their effects on muscles, your liver and
your heart, can lead to problems with breathing and heart function.
This can sometimes lead to death which can occur at a very early age in
some cases.
Your doctor will be able to discuss the outlook for
a particular glycogen storage disorder in more detail. The possibility
of new treatments and therapies are constantly emerging. Enzyme
replacement therapy and gene therapy mean that, hopefully, the outlook
for glycogen storage disorders will soon be greatly improved.
Can glycogen storage disorders be prevented?
Glycogen
storage disorders are hereditary conditions that run in families. If
someone else in your family, or if you yourself, or one of your
existing children, has a glycogen storage disorder, your doctor may
refer you to a geneticist (a gene specialist). The geneticist will be
able to discuss the likelihood of your future child, or children,
having a glycogen storage disorder.
When a woman becomes
pregnant, there is also the possibility of having some tests carried
out early in the pregnancy to determine if the unborn baby has a
glycogen storage disorder. The tests involve taking a sample of
amniotic fluid from around the baby. This allows the doctor to study
the levels of the enzymes in the amniotic fluid and therefore determine
whether the unborn baby has a glycogen storage disorder.
Further help and information
The Association for Glycogen Storage Diseases (UK)
9 Lindop Road, Hale, Altrincham WA15 9DZ
Tel: 0161 980 7303
Web: www.agsd.org.uk
Offers support for affected individuals and families and linking of
families where possible. Can provide information about current
treatments and long term prospects for people with glycogen storage
disorders.
Contact a Family
209-211 City Road, London EC1V 1JN
Tel (Family Advice Helpline): 0808 808 3555 Tel (Minicom): 0808 808 3556
Web: www.cafamily.org.uk
Has the primary aim of encouraging mutual support between families of disabled children.
References
-
Visser G, Rake JP, Labrune P, et al;
Consensus guidelines for management of glycogen storage disease type 1b
- European Study on Glycogen Storage Disease Type 1. Eur J Pediatr.
2002 Oct;161 Suppl 1:S120-3. Epub 2002 Sep 13. [abstract]
-
Chou JY, Mansfield BC; Gene therapy for type I glycogen storage diseases. Curr Gene Ther. 2007 Apr;7(2):79-88. [abstract]
-
Koeberl DD, Kishnani PS, Chen YT;
Glycogen storage disease types I and II: treatment updates. J Inherit
Metab Dis. 2007 Apr;30(2):159-64. Epub 2007 Feb 16. [abstract]
-
Ozen H; Glycogen storage diseases: New perspectives. World J Gastroenterol. 2007 May 14;13(18):2541-53. [abstract]
-
Kishnani PS, Hwu WL, Mandel H, et al;
A retrospective, multinational, multicenter study on the natural
history of infantile-onset Pompe disease. J Pediatr. 2006
May;148(5):671-676. [abstract]
Comprehensive patient resources are available at www.patient.co.uk
© EMIS and PiP 2008 Updated: 19 Mar 2008 DocID: 8690 Version: 1
