ACID MALTASE DEFICIENCY: WHAT IS ACID MALTASE DEFICIENCY?
Definition: What is "Acid maltase deficiency"?
Acid maltase deficiency or AMD is a type of autosomal recessive disorder which is characterized by an extreme buildup of glycogen contained by vacuoles (in almost all cell types) that are lysosome-derived. Quantities of free extralysosomal glycogen that are in excess have also been depicted. AMD was first observed & described by JC Pompe in 1932 at Amsterdam. He reported a case of a baby girl, aged 7 months, who became chronically ill from what they believed to be pneumonia. The autopsy that was done later showed an uncommonly engorged heart but with normal valves. This condition was called cardiomegalia glycogenica diffusa by Pompe. He considered it as a disorder that is analogous to the von Gierke syndrome. This very first article was soon followed by reports that seemed similar. The two other authors described the children as afflicted with cardiomegaly & acute muscle weakness. They died in their early infancy. Their disease was linked to an excess in the deposition of glycogen in numerous tissues. This disorder was then named the Pompe disease & by the year 1957, it was typified as type 2 glycogenosis by GT Cori.
The Pompe disease or infantile acid maltase deficiency arises in 1 out of the 50,000 births in the United States.
Mortality or Morbidity
AMD is a disease that can be inherited & it is an autosomal recessive disorder. In its infantile form, death commonly occurs from 6 months until the second year of life. The less severe form of infantile AMD has improved survival rates & better prognosis. The patients who suffer from late infantile AMD may live for several more years. Those who suffer from the adult & juvenile forms are recorded to have survived into their sixth or the seventh decades of existence. The clinical symptoms may come in various presentations & few cases may be undetectable; therefore, the patients' life expectancy under this group cannot be known exactly.
Clinical Phenotypes of AMD
There are 4 recorded phenotypes of AMD & they are the following: juvenile, adult, late infantile & infantile (or the Pompe disease). The Pompe disease of infantile acid maltase deficiency is the most common example of a myopathy that is metabolic in nature & a motor neuron disorder which causes infantile hypotonia. This type of disease is the most acute & it carries with it the worst possible prognosis (where death results in between the sixth month & the second year of life). All the other forms are milder & have various clinical presentations.