Pompe disease, or acid maltase deficiency, is defined as an autosomal recessive metabolic disease that destroys muscle along with nerve cells throughout the body.
The disorder is initiated by a build-up of glycogen in the lysosome as a result of deficiency of the lysosomal acid and GAA enzyme. GAA enzyme is accountable for cracking down glycogen in the lysosome. In Australians afflicted with Pompe Disease, the GAA enzyme is either absent or present but in very low amounts and glycogen forms in the lysosome, leading to symptoms related to this disease. Pompe disease is approximated to occur in roughly one in forty thousand births globally, including Australia.
The connection that exists between genotypes and phenotypes is firm, in that Australians with the most life-threatening phenotype, classic infantile Pompe syndrome, have two pathogenic transformations, one in each GAA allele, that inhibit the formation of GAA or totally destroys its function.
Pompe disease progression is relentless with death normally by the age of two years. Similarly, in the young form, the disease is deadly within a few months of onset of heart failure. In the adult disease, prognosis rests on the degree of respiratory involvement. Ventilator aids, including nocturnal intermittent positive pressure ventilation may be used to support the patients.
Types of Pompe Disease
In Australia, the disease is classified in different phenotypes in accord to their severity. The earlier the onset, the more severe, faster as well as worse the development is, this is so since the deficit of GAA is more severe. As a matter of fact, there is no clear division into phenotypes, but a continuous range from the complete lack of GAA that leads to severe signs in early infancy to the slightest disease that starts in adulthood and produces only slight and steady respiratory distress along with limbs weakness. Generally, there are two types of Pompe disease, which include infantile-onset Pompe disease and late-onset Pompe disease.
Infantile-onset pompe disease: onset is before one year of age and it is subdivided into classic infantile disease and non-classic infantile disease. Classic infantile disease starts in the first months of age and progresses rapidly to death before two years of age. Non-classic infantile disease has a lower evolution.
Late-onset disease: Has symptoms that appear after the first year of age, and it is subdivided into juvenile and adult form. It is difficult to date the onset in the event that the course is slow.
The onset of the symptomatology is associated with the grade of enzyme deficit, but also with other factors, which can be modifiers genes or non-genetic. In the event that the enzymatic activity is below 1%, the muscular dysfunction is so severe than a classic infantile form. On the other hand, when the enzymatic activity is above 10%, the muscle degenerates more slowly, thus resulting to a juvenile or adult form. Children with classic pompe disease have disorders of sucking, swallowing or feeding from birth or the first months of age. This results in low weight gain and respiratory infections and failure, due to diaphragm involvement.
1. Infantile onset of pompe guidelines 2013: http://www.health.gov.au/internet/main/publishing.nsf/Content/lsdp-info/$File/infantile-onset-pompe-guidelines-june-2013.pdf
2. Pompe disease: http://en.wikipedia.org/wiki/Pompe_disease