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PatientsFAQs on Liver DiseasesGlycogen Storage Disease
PatientsFAQs on Liver DiseasesGlycogen Storage Disease Glycogen Storage Disease
- What is a glycogen storage disease?
- A glycogen storage disease is a genetic defect that causes a metabolic enzyme to become inactive. It inhibits a cell's ability to either generate or utilise glycogen.
- How do we get glycogen storage diseases ?
- Glycogen storage diseases are inherited from parents who carry copies of a defective gene.
- What are the general symptoms of glycogen storage diseases?
- Symptoms vary among the types of glycogen storage diseases, but common symptoms include low blood sugar, enlarged liver, retarded growth, and abnormal blood biochemistry.
- Are all glycogen storage diseases fatal?
- No. Depending on the type of disease, the ethnic background and lifestyle of the patient, some glycogen storage diseases may be so mild that they go unnoticed.
- How are glycogen storage diseases diagnosed?
- A definite diagnosis can be made by testing a liver biopsy sample for glycogen concentration, and by assaying the sample for enzyme activity. Distinguishing symptoms of glycogen storage diseases are type-specific.
- In a suspected glycogen storage disease, what information could be gained from a liver biopsy?
- A liver biopsy could determine the activity of one of several enzymes in question. It might be used to make a firm diagnosis in suspected cases of von Gierke's Disease or Pompe's Disease. However, a liver biopsy is an invasive procedure and should only be performed when a definite diagnosis cannot be made by other methods.
- How might a carrier for a glycogen storage disease be diagnosed?
- An allele-specific oligonucleotide hybridization test, if positive, would be conclusive.One could also use full-length human cDNA that has the gene sequence for the enzyme in question (e.g. glycogen phosphorylase for McArdle's Disease) as a probe for restriction fragment length polymorphism (RFLP).
- What is the approximate frequency of occurrence of Pompe's Disease in live births?
- 1 in 100,000
- Why do patients with McArdle's Disease often excrete burgundy-colored urine?
- Their urine contains myoglobin, which is burgundy-colored.
- Are glycogen storage diseases dominant or recessive?
- All glycogen storage diseases are recessive.
- In order for a child to have a glycogen storage disease, must both parents have a defective gene?
- Yes. Both parents must have at least one defective copy of the gene, but neither parent must express the disease.
- When is the mother described as a "carrier" for a glycogen storage disease.?
- This means she has two copies of a gene that codes for an enzyme involved in glycogen storage; one copy is healthy, the other is defective. She can pass along either copy to her offspring with equal probability. (If the father is also a carrier, their offspring has a 25% chance of inheriting the disease, and a 50% chance of becoming a carrier.)
- Which organs and tissues are most directly affected by glycogen storage diseases?
- The liver is the body's primary repository of glycogen, so most glycogen storage diseases have a direct adverse effect of the liver. These diseases also affect muscle tissue, which must comply with sudden demands for energy.
- Which enzyme is deficient in McArdle's Disease?
- Glycogen phosphorylase, the enzyme that releases glucose from the non-reducing end of a glycogen polymer.
- Why do patients with McArdle's Disease experience muscle cramps and fatigue?
- Their muscles lack the glucose necessary for ATP production(energy source). Note: since little glucose is available to start with, glycolysis does not form lactate in large quantity. Therefore muscle fatigue is not the result of lactic acid buildup. This is a common misconception about McArdle's Disease.
- What is an alternate energy source for patients with McArdle's Disease?
- Creatine kinase can convert phosphocreatine into creatine, meanwhile phosphorylating ADP to make ATP. However, this process provides energy for only about four seconds of physical exertion.
- Which enzyme is deficient in Pompe's Disease?
- Lysosomal-1,4-glucosidase, also known as acid maltase, which is normally responsible for digesting glucose in lysosomes.
- Why does Pompe's Disease affect every organ in the body?
- Pompe's Disease affects the functions of lysosomes, which are found in all types of tissue.
- Why is Pompe's Disease sometimes called Acid Maltase Deficiency?
- The interior of a lysosome is more acidic than the cytosol, and lysosomal enzymes are more active at low pH than at neutral pH.
- Which enzyme is deficient in von Gierke's Disease?
- Glucose-6-phosphatase, the enzyme that converts glucose-6-phosphate to glucose as it passes from the cytosol into the endoplasmic reticulum in the liver.
- What reaction is catalyzed by glucose-6-phosphatase?
- Glucose-6-phosphatase catalyzes the conversion of glucose-6-phosphate to glucose.
- Where in the body is glucose-6-phosphatase located? Where is it not located?
- Glucose-6-phosphatase is located in liver and kidney cells. It is not located in muscle or brain cells.
- Why can't glucose-6-phosphate cross the endoplasmic reticulum membrane?
- Glucose-6-phosphate is negatively charged. Only uncharged molecules can cross the membrane.
- What treatments exist for glycogen storage diseases?
- There are no cures for any of the glycogen storage diseases. The less severe diseases can be treated with dietary restrictions, usually high-protein, low-carbohydrate diets. Palliative care may be the only option in more severe cases.
- How long must dietary restrictions continue?
- Dietary restrictions must continue throughout life.
