In late-onset Pompe disease, unlike the infantile-onset form, there is a low level of GAA enzyme. It can be diagnosed from age one but is also known to present much later in life.
Enzyme Replacement Therapy
Until a treatment became widely available in 2006 management was primarily through diet and physiotherapy.
An Enzyme Replacement Therapy (ERT) was developed and is now widely available. It is a costly treatment available under the Orphan Drug Act.
The only current ERT is called Myozyme (Alglucosidase alfa), produced by Sanofi Genzyme Ltd. Though now routinely available in England, it is not assured for every adult patient in Wales and Scotland where individual applications must be made.
Once diagnosed it is important for treatment suitability to be assessed. The European Pompe Consortium (EPoC) has issued treatment guidelines for starting ERT.
What ERT involves
ERT involves giving a manufactured, replacement enzyme in to the body. This aims to help the body process glycogen and reduce build-up in the lysosomes.
This is a lifelong treatment given every two weeks. The dose is based on a person’s weight. It is given directly in to the blood stream by a trained nurse. This requires a needle to be inserted in to a vein (cannulation). A few people later have a port fitted (this is a device that remains in the skin and allows for the infusion to happen via the port without cannulating every time).
The first infusions are given in hospital and are closely monitored. Blood and urine samples will be taken and checked. The whole process, from start to finish can take several hours, more if you are a large person. The infusion is given slowly, partly to help avoid an allergic reaction. Due to the cost of the drug it comes in lots of small vials and not one large one. These glass vials contain a powder which must be mixed with a liquid [reconstituted]. The mixing is done very slowly because the drug is treated gently and should not be shaken.
After several successful hospital-based infusions you may switch to home infusions. A trained nurse from a home-care company employed by the NHS will give the infusions. These nurses are specially trained. Although infusions seem daunting at first, most people get used to them eventually. Some people have them at school or college and others in their work place.
Sometimes patients have an allergic reaction to the ERT. Nurses closely check for this, especially during the early hospital-based infusions. Patients are advised to look out for; sweating, shortness of breath, feeling hot or a skin rash. Patients who experience a reaction receive extra care and monitoring. They might return to hospital for their next few infusions and have drugs to reduce the allergic reaction. The infusions can sometimes be restarted, initially at a slower rate than before, slowly building back up to the usual rate.
Living life with ERT
Enzyme Replacement infusions at home involve some organising, managing of diaries and ordering of treatment consumables. When starting home-infusions it is really good time to get in touch with someone who has this experience.
The Myozyme is delivered by cold chain and kept at a steady temperature so someone needs to be at home to receive it. Patients will also order the items needed by the nurse such as needles and sharps bins for disposing of used needles safely. Again, someone has to be at home to receive them.
The infusion also uses a pump, this must be stored and looked after and filters need to be changed. An infusion nurse will usually change filters.
A range of assessments
Here are some other tests that you might be given during appointments:
- Nerve conduction test for muscles (EMG)
- Overnight sleep assessment
- Videofluroscopy to check swallowing
- ECG and Echocardiogram to check heart size and function
- Blood tests to check creatine kinase (CK) levels and alanine transaminase (ALT) levels amongst others
Late-onset Pompe disease is associated with a gradual loss of muscle function over time. Loss of breathing muscle strength can lead to an ineffective cough. As time progresses breathing complications need to be managed. Patients will have regular breathing assessments and sometimes stay overnight in hospital for a sleep study. These can now sometimes be done at home if equipment is available.
Weakened breathing muscles can lead to poor sleep and low oxygen levels. This can cause the common morning headache and fogginess often mentioned by people affected by Pompe disease. It is wise to ask about having a ‘flu and/or pneumonia jab at your GP surgery. A very impaired cough can be helped by a cough-assist machine.
Many people also have a non-invasive ventilator. This is a machine that helps breathing, especially during the night and sometimes during the day as well.