Pompe Disease

Original Editor - Chelsea Mclene Top Contributors - Nupur Smit Shah, Chelsea Mclene, Kim Jackson and Lucinda hampton  

Introduction

Pompe's disease is a rare, inherited, severe neuromuscular disease and often fatal disorder. It disables the heart and skeletal muscles and is caused by mutations in a gene that makes an enzyme called acid alpha-glucosidase (GAA). It is also an autosomal recessive disorder due to deficiency of a lysosomal enzyme, acid maltase. Among various glucogenosis, pompe;s disease is the only example of lysosomal storage disease. It affects both males and females.

Causes and Inheritance

Glycogen is a form of sugar that the body stores in cells of the liver and skeletal muscles, and works as a long-term reserve of energy. When the body needs energy, this large molecule is broken down into smaller molecules of a simpler sugar called glucose. Certain proteins are needed for this process. A mutation in the GAA gene can either prevent the production of this enzyme, or create an enzyme that does not work as intended. In either case, glycogen cannot be broken down and builds to toxic levels inside cells, impairing certain organs and systems, particularly the muscles.

Pompe disease is inherited in autosomal recessive disorder which means the disease only develops in people who inherit two faulty copies of the gene, one from each parent. The signs and symptoms are not seen in individuals who have one faulty gene. They are called carriers because they can pass the disease onto their children. When both parents are carriers, child has 50 percent chance of inheriting one mutated gene and also becoming a carrier, and a 25 percent chance of inheriting two healthy genes and neither developing the disease nor being a carrier.

Types

Classic infantile-onset

It appears within a few months of birth. Infants experience muscle weakness, poor muscle tone, an enlarged liver, breathing problem, heart defects, fails to gain weight and grow at the expected rate. If untreated, leads to death from heart failure in the first year of life.

Non-classic infantile-onset

It appears at about 1 year of age. It is characterized by delayed motor skills and progressive muscle weakness. The heart may be abnormally large, but affected individuals usually do not experience heart failure. The muscle weakness in this disorder leads to serious breathing problems, and most children live only into early childhood.

Late-onset

It appears later in a child’s life, or even into the teen years or adulthood. It is usually milder than the infantile-onset forms of this disorder and is less likely to involve the heart. Most individuals experience progressive muscle weakness, especially in the legs and the trunk, including the muscles that control breathing. As the disorder progresses, breathing problems can lead to respiratory failure.

Symptoms

Classic type

• Weak muscles
• Poor muscle tone
• Feeding problems
• Infections in the respiratory system
• Problems with hearing
• Enlarged liver
• Failure to gain weight and grow at the expected rate
• Trouble breathing

Non-classic type

• Motor skills delayed
• Breathing problems
• Muscles get steadily weaker
• Abnormally large heart

Late-onset type

• The legs and the trunk get steadily weaker.
• Loss of the ability to exercise
• Falling often
• Breathing problems
• Enlarged heart
• Increasing difficulty in walking
• Losing weight
• Cannot swallow as easily as before
• Irregular heart beat
• Increased difficulty hearing
• Muscle pain over a large area
• Frequent lung infections
• Shortness of breath when the person pushes himself or herself
• Headaches in the morning
• Becoming tired during the day
• Higher levels of creatine kinase

Diagnosis

Pompe disease is first diagnosed with clinical findings particularly those related to breathing problems and evidence of muscular weakness. Differential diagnosis is important as it is wrongly assumed to be a different chronic and muscle-wasting disease. To confirm, the activity of the GAA enzyme in cells obtained from the skin, muscles, or blood is accessed. Testing for GAA gene mutations can help confirm the diagnosis, and is particularly helpful in identifying carriers. Prenatal diagnosis may be available for couples with a child affected by the disease.

Treatment

Pompe disease patients are followed by a multidisciplinary team of specialists, including cardiologists, neurologists, pulmonologists, respiratory therapists, metabolic specialists, dietitians, orthopedists, occupational/speech therapists, geneticists, and genetic counselors. Enzyme replacement therapy may help reduce the buildup of glycogen inside cells, and slow the progression of the disease. A drug called alglucosidase alfa is given intravenously. It is a genetically engineered enzyme that acts like the naturally occurring acid alfa glucosidase enzyme.

Physiotherapy: A physiotherapist can help by implementing and monitoring a light exercise routine that may involve walking, cycling, swimming or strength training to maintain muscle strength in people with Pompe disease. It is important to not perform excessively strenuous exercise, though, because it may cause more muscle damage.