Diagnosis

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To sum up on the topic of McArdle Disease, we will be talking about how the diagnosis step taken.

Before that, let's have a overall view of how glucose is broken down in the cells when it undergoes anaerobic glycolysis.

The Diagnosis

Diagnosis of Glycogen Storage Disease Type V will commence if the doctor notices that patient possesses multiple of the symptoms indicated for this disease. Firstly, laboratory tests will be carried out. A muscle biopsy will be carried out to find out if there is an absence of myophosphorylase found in muscle fibers. A microscope can also be used to view acid-Schiff stained glycogen in some cases.

Genetic sequencing of the PYGM gene, which is responsible for the coding of myophosphorylase, may be done to determine if there is indeed a mutation in the gene and hence determining the presence of McArdle's disease. This testing is preferred due to its less invasive nature as compared to conducting a muscle biopsy.

- one mouthwatering burger from our restaurant

That's all from us! We hope that you have enjoy the meal throughout the whole course and learn more about the facts of McArdle Disease.

This will be our last time posting as our restaurant is moving out of Ngee Ann Polytechnic, School of Life Science & Chemical Technology, Blk83 B1-01 with effect of today 2359. :)


http://www.patient.co.uk/doctor/mcardles-disease-glycogen-storage-disease-type-v
http://en.wikipedia.org/wiki/Glycogen_storage_disease_type_V#Diagnosis

Biochemistry

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We are back from the Common Test week and will continue update this space! :D

Let's start off with the Biochemistry of Glycogen

Glycogen is principally found in muscle and liver cells, where it is stored as an energy source readily converted into glucose whenever our body requires energy. When muscle cells require energy, glycogen will be converted to ATP.

As seen from the picture, glycogen is actually comprised of linked alpha-D-glucose monomers that form linkages by either alpha-1,4 or alpha-1,6 linkages.

Glycogen Breakdown

Glycogen is broken down by glycogen phosphorylase. The reaction is non hydrolytic as water molecules are not produced upon the breakdown. Glycogen phosphorylase combines inorganic phosphate with the non reducing terminal glucose residue to form glucose-1-phosphate. 

Disease

When someone actually contracts McArdle's Disease, they're ability to synthesize glycogen phosphorylase is not impaired, but due to mutations in the gene coding for Myophosphorylase, they are unable to execute their normal function of breaking down glycogen into glucose, as such, mucles are deprived of glucose with is then converted to ATP via other metabolic pathways, which thus leads to accelerated muscle fatigue and glycogen remains accumulated in muscle tissues, hence the name Glycogen Storage Disease.

References
https://www.uic.edu/classes/phar/phar332/Clinical_Cases/carbo%20metab%20cases/glycogen%20metab/Glycogen%20biochemistry.htm

http://medicinembbs.blogspot.sg/2011/02/genetic-diseases.html

http://www.nlm.nih.gov/medlineplus/ency/article/000329.htm

http://en.m.wikipedia.org/wiki/Glycogen_storage_disease_type_V

http://mcardlesdisease.org/

http://www.patient.co.uk/doctor/mcardles-disease-glycogen-storage-disease-type-v

Symptoms of McArdle Disease

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As mentioned in the previous post "Causes of McArdle Disease", it is mentioned that due to a nonsense or missense mutation in the PYGM gene that is coding for myophosphorylase. As a result, muscle cells cannot produce enough energy, so muscles become easily fatigued.

Phosphorylase deficiency causes exercise intolerance, such as cramps, muscle pain and weakness, shortly after beginning exercise.

A person with this disorder may tolerate light-to-moderate exercise such as walking on level ground, but strenuous exercise usually will bring on symptoms quickly. Resting may lead to a “second wind,” in which activity is then better tolerated. Isometric exercises that require strength, such as lifting heavy objects, squatting or standing on tiptoe, also may cause muscle damage.

Symptoms of this disease vary in severity among people and even within the same person from day to day. Symptoms usually don’t persist between attacks, although fixed weakness later in life is possible.

The symptoms are as followed: 

• Burgundy-colored urine (myoglobinuria)
• Fatigue
  
• Exercise intolerance, poor stamina 
  
• Muscle cramp, pain, stiffness, weakness 

Glycogen Storage Diseases

BARBECUE SAUCE

Here's an illustrated video on the different kinds of Glycogen Storage Disease that exist. 

For McArdle Disease (4:32 - 5:14)

We hope this broaden your understanding on the different kind of Glycogen Storage Disease! 

Causes of McArdle Disease

Good Morning! :D

We certainly hope that your future Tuesday is not as blue as Monday because we are updating this space regularly on Tuesday. We will also post interesting news articles, videos and animations to allow better understanding of this disease if we come across any. 

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For exercising muscles, one of the important energy sources is anaerobic glycolysis, which makes use of blood glucose, which will be converted to glucose-6-P inside the muscle cells. The final product of anaerobic glycolysis is lactate.

The phosphorylase, glycogen, muscle (PYGM) gene provides instructions for making an enzyme called myophosphorylase (M-GP). This enzyme breaks down a complex sugar called glycogen.


[extra titbits] 

Where is the PYGM gene located?

Cytogenetic Location: 11q12-q13.2

Molecular Location on chromosome 11: base pairs 64,746,388 to 64,760,714

The PYGM gene is located on the long (q) arm of chromosome 11 between positions 12 and 13.2.

More precisely, the PYGM gene is located from base pair 64,746,388 to base pair 64,760,714 on chromosome 11.

[/extra titbits] 


Myophosphorylase is one of three related enzymes called glycogen phosphorylases that break down glycogen in cells. Myophosphorylase is found only in muscle cells, where it breaks down glycogen into a simpler sugar called glucose-1-phosphate. Additional steps convert glucose-1-phosphate into glucose, a simple sugar that is the main energy source for most cells.

The most common cause of McArdle's Disease is due to a nonsense or missense mutation in the PYGM gene that is coding for myophosphorylase. As a result, muscle cells cannot produce enough energy, so muscles become easily fatigued. The most common form of mutation is the nonsense mutation at the 49th codon (R49X).

The essential reaction for converting glycogen into glucose is as shown in the image below.

As patients suffering from McArcle's Disease is unable to use the glycogen stored in his muscle to obtain energy, due to the lack of muscle glycogen phosphorylase to convert glycogen into glucose-1-P, Due to their inability to degrade glycogen, it will accumulate in the muscle tissues and hence the other name Glycogen Storage Disease Type V. The patient will present fatigue much earlier in tests and the concentration of lactate in the blood is much lower than normal. However, blood glucose levels are not affected because muscle glycogen does not buffer blood glucose.

I hope this is not too overwhelming and satisfies your hunger for the knowledge! We will try to source for interesting pictures/videos so that it's better to digest the BUNS that we feed you. 

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Welcome to MacDonald

This is our special menu for the branch located in Ngee Ann Polytechnic, School of Life Science & Chemical Technology, Blk83 B1-01. 

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Alright, I see that you have chosen our restaurant best course meal. (McArdle served with Medical Biomolecular Chemistry knowledge). That will be free for you as long as you keep a lookout to this space every Tuesday as we will be serving you all new interesting and mouth watering facts on the disease state called: McArdle disease, or also known as muscle phosphorylase (myophosphorylase) deficiency.

So are you ready for the appetizers? 

Glycogen storage disease type V (also known as GSDV or McArdle disease) is an inherited disorder caused by an inability to break down a complex sugar called glycogen in muscle cells. A lack of glycogen breakdown interferes with the function of muscle cells. 

People with GSDV typically experience fatigue, muscle pain, and cramps during the first few minutes of exercise. Exercise such as weight lifting or jogging usually triggers these symptoms in affected individuals. The discomfort is generally alleviated with rest. If individuals rest after brief exercise and wait for their pain to go away, they can usually resume exercising with little or no discomfort. Prolonged or intense exercise can cause muscle damage in people with GSDV.

About half of people with GSDV experience breakdown of muscle tissue (rhabdomyolysis). In severe episodes, the destruction of muscle tissue releases a protein called myoglobin, which is filtered through the kidneys and released in the urine (myoglobinuria). Myoglobin causes the urine to be red or brown. This protein can also damage the kidneys, and it is estimated that half of those individuals with GSDV who have myoglobinuria will develop life-threatening kidney failure.

The signs and symptoms of GSDV can vary significantly in affected individuals. The features of this condition typically begin in a person's teens or twenties, but they can appear anytime from infancy to adulthood. In most people with GSDV, the muscle weakness worsens over time; however, in about one-third of affected individuals, the muscle weakness is stable. Some people with GSDV experience mild symptoms such as poor stamina; others do not experience any symptoms. 

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That's for all this post today. I hope this has stimulate your hunger to know more about McArdle Disease. Do contain your hunger pangs and we will be feeding you with more information next week.

Have a great week ahead!