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Also known as Glycogen storage disease (GSD) type II, Glycogenesis type II, Acid Malatase Deficiency

Introduction

Pompe disease is an inherited, genetic disorder which results in the lack of an enzyme 'acid alpha-glucosidase’. Pompe disease is also known as acid maltase deficiency or glycogen storage disease type II. To understand the implications of this it is useful to know a little about this enzymes normal activity. The human body contains many different types of cells.

A basic cell has many components as you can see from the diagram below, including the nucleus which contains chromosomes. Within the cell there is a small compartment called the lysosome - this contains all the enzymes the cell needs to manage its recycling of waste products.

The enzymes in the lysosome begin the process of breaking down glycogen but in Pompe disease this is ineffective. The glycogen accumulates in various types of muscle – skeletal (eg limb, body & respiratory muscle) , smooth (eg the muscles involved in feeding/swallowing) and cardiac (heart muscle – predominantly in children).

Inheritance

Pompe disease is an inherited genetic disorder described medically as an 'autosomal recessive disease’.  Each person has 23 pairs of chromosomes which contain genes – they receive 1 set from each parent. Genes contain the necessary information to allow our body to be formed and to function. It is estimated that every human being has 8 -10 genes that have changes within them (called mutations) however only some can cause disease. Pompe disease only produces symptoms when both copies of the gene are affected. This may well have occurred when both parents have 1 copy of the genetic mutation. They are said to be carriers (ie without any evidence of disease) but their offspring may inherit both copies of the faulty gene.

There are other possibilities – eg if 1 parent has Pompe disease and the other either has no mutation or is a carrier. In the former case all the children will be carriers and the latter there is a 50% chance of having an affected child and a 50% chance of a carrier.

If you would like further information about the inheritance pattern in your personal circumstances or to know whether it is likely that any other members of your family are affected please discuss this with your physician or specialist nurse.

Symptoms

The signs and symptoms of Pompe disease are directly related to the muscles affected. The disease is progressive in nature, and affects proximal, respiratory and cardiac (infants) muscle.

There are currently thought to be 2 main types of Pompe disease:

Infantile

  • Classic infantile Pompe is the most severe end of the spectrum with rapidly progressive cardiomegaly (enlarged heart) hepatomegaly (enlarged liver) weakness and hypotonia ('floppy’). This leads to early death usually in the first year of life
  • Infantile variant Pompe has a slower progression and less severe cardiomegaly. It usually presents during the first year of life

Late onset

  • Juvenile pompe presents later than infancy and typically does not include severe cardiomyopathy
  • Adult onset is characterised by a slowly progressive myopathy (muscle weakness) that presents as an adult

The severity of the disease and the rate of disease progression varies from person to person. Listed below are the possible symptoms:

 

Infantile  onset

Adult onset

Cardiac

Cardiomegaly (enlarged heart)
Cardiomyopathy
(weak heart)

rarely seen

Musculoskeletal Profound/rapidly progressive  - hypotonia (floppy baby)
Delayed motor milestones
Progressive proximal muscle weakness 
(esp. trunk and lower limbs)
Gait abnormalities
Muscle pain
Difficulty climbing stairs
Frequent falls
Scapular winging
Respiratory

Frequent infections
Respiratory insufficiency
Cardio-respiratory failure (death)

Respiratory failure/insufficiency
Morning headache & day time tiredness
Orthopnea ( breathing difficulties when laying down)
Sleep apnea ( stopping breathing whilst asleep)
Exertional  shortness of breath
Respiratory infections
Gastrointestinal

Failure to thrive, feeding difficulties
Organomegaly – enlarged liver, spleen & tongue

Jaw muscle fatigue & swallowing difficulties
At risk of food aspiration
Weight stability
Other

Osteoporosis/osteopenia
Neurological & hearing impairment

Osteoporosis/osteopenia

Treatment

Enzyme replacement therapy (ERT)

Until recently in the UK treatment for Pompe disease was limited to supportive therapy. In April 2006 Genzyme corporation received a product licence for Myozyme. This is the direct replacement of the missing enzyme in Pompe disease a treatment known as enzyme replacement therapy (ERT) This is an intravenous infusion that is give once per fortnight initially in hospital but with the possibility of home infusion if hospital infusions are uneventful. The infusion takes between 4-5 hours to give.Patient receiving an intravenous infusion of Myozyme

This treatment is considered to be an “orphan drug" and as such prescribing in England is restricted to NCG centres. In Scotland, Wales and N Ireland, permission must be obtained from the devolved NHS authorities in each region.

Side effects are generally mild but may include:

  • Hypersensitivity – anaphylactic shock has been reported in a few patients
  • Infusion reactions – agitation, tremor, tachycardia (fast heart rate), cyanosis, flushing, hypertension (high blood pressure), pallor, tachypnoea (fast breathing), cough, vomiting, urticaria (rash), fever, rigors (chills), decreased oxygen saturation, hypotension (low blood pressure) & tachycardia (fast heart rate)

Note: reactions are more likely if a patient has an acute underlying illness at the time of the infusion, or if they have reacted to myozyme before.

Supportive treatment

This will vary considerably depending upon the nature and severity of the symptoms experienced. Pompe is a progressive disorder and therefore requires regular assessment to identify which treatments are appropriate. In general these tests should include assessment of cardiac and respiratory function (heart and lung), muscle strength and function, safety when swallowing and diet/weight maintenance.

It is likely that people affected by pompe will also need to visit other doctors eg a neurologist, respiratory and/or cardiac physician as well as other healthcare professionals such as the physiotherapist, occupational therapist, speech therapist and dietician. At Addenbrooke’s, Pompe patients are cared for by an experienced metabolic physician and a specialist nurse who will co-ordinate assessment, treatment and supportive care as necessary, with access to the multi disciplinary team. The input and support of a local physician is also essential.

It is considered important for patients to adopt a healthy lifestyle by following dietary advice, exercising within limits and to avoid smoking in order to maintain or improve general health.