What else is it called?
- Antopol disease
- Glycogen storage disease type 2B
- Lysosomal glycogen storage disease with normal acid maltase
- Pseudoglycogenosis II
- Vacuolar cardiomyopathy and myopathy, X-linked
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What causes it?
Danon Disease is caused by a problem in the LAMP2 gene. This gene produces the LAMP-2 (Lysosomal Associated Membrane Protein-2) enzyme, which is involved in the process of digesting and recycling damaged or obsolete materials in your cells. The process is needed to keep cells healthy and to reduce the risk of disease or the effects of damage.
If you have a problem in the LAMP2 gene, you will not produce enough of the LAMP-2 enzyme. Therefore, you will be unable to recycle and remove the redundant material in your cells, and this causes an unusually large number of gaps in your tissue (called autophagic vacuoles) which can cause muscle cells to break down.
How common is it?
Danon Disease is an extremely rare disorder. As a result, the exact prevalence is currently unknown. It is believed to affect all ethnicities equally.
Although Danon Disease affects both males and females, the symptoms are more profound in males because it is inherited through the X chromosome. Females have two X chromosomes, whereas males only have one, so females are likely to have one working chromosome to compensate for any problems caused by the other.
What are the signs and symptoms?
The main symptoms for Danon Disease include:
- Weakening and enlargement of the heart muscles (dilated cardiomyopathy)
- Thickening of the heart muscles (hypertrophic cardiomyopathy)
- Weakening of the muscles used to move (skeletal myopathy)
- Intellectual disability
- Fluttering or pounding in the chest (palpitations)
- Abnormal heartbeat (arrythmia)
- Chest pain
- Abnormality of the electrical signals controlling the heart (conduction abnormalities)
Some individuals also have symptoms such as gastrointestinal disease, breathing problems, or visual issues.
These symptoms appear to affect males more frequently than females, who may have mild or fewer symptoms. Almost all people with Danon Disease will experience severe heart problems. However, again, males are likely to encounter these earlier than females.
Life expectancy is an average of 19 years old for males and 34 years old for females.
How is it diagnosed?
Danon Disease is difficult to diagnose due to its rarity. Medical professionals may look at your symptoms and your family history to consider the likelihood of you having this disorder.
A muscle biopsy is carried out to look at your cells. This involves removing a very small amount of tissue from your body for microscopic analysis. It is a simple procedure and isn’t usually painful, but it may feel briefly uncomfortable.
Your diagnosis will be confirmed using a genetic test.
If your parent, child, or sibling is diagnosed with Danon Disease, it is possible that you will also have the disorder. Speak to your medical team to see if you need to be tested.
Can it be treated?
There is currently no cure for Danon Disease. Treatment usually focuses on managing the symptoms, paying particular attention to any heart problems you may experience.
You may be given an implantable cardioverter-defibrillator, which is a machine connected to your heart that will shock it whenever it detects that the rhythm is irregular. In other cases, you may require surgery to repair your heart, up to and including a heart transplant.
Other treatments include medication, occupational and/or speech and language therapies for any intellectual disabilities, and physical therapy to support weakened muscles.
Life expectancy may be increased by a heart transplant, however a significant amount of people with Danon Disease are at high risk of complications including death during surgery.
Most people with the disorder will suffer from congestive heart failure or another significant life-threatening event. Males with the condition do not typically live beyond 19 years of age, whereas females are expected to live to 34 years old.
Do my family need to be tested?
Danon Disease is inherited from your parents through your X chromosome. Every person has two chromosomes – one from your mother and one from your father – that determine our DNA. Everybody receives an X chromosome from their mother. Males receive a Y chromosome from their father and females receive an X chromosome. This is what determines our sex.
Because males only have one X chromosome, if the LAMP2 gene is faulty, there is no ‘back-up’ from their Y chromosome. This means that they will have Danon Disease. However, girls with the faulty LAMP2 gene will have an extra, working gene that will reduce the symptoms of the disorder slightly.
Mothers who are affected have a 50% chance of passing Danon Disease to their child, regardless of gender. There is a 50% chance that their child will be born without the faulty gene.
Fathers who are affected by Danon Disease cannot pass it onto their sons. However, any daughters they have will be affected by the disorder.
If you think that you or somebody in your family may be affected by this disorder, contact your medical team to explore the possibility of genetic testing so that you can get the support you require.
References are available on request. Please contact Helen Morris by phoning 0845 241 2173 or emailing firstname.lastname@example.org [Resource Library No: AAP002].