This week we will be a little more intensive and examine the science behind Pompe. Are you ready?! Of course you are! I can sense your enthusiasm!! XD Now lets get started shall we?
As mentioned in the previous post, Pompe patients are unable to break down glycogen in their cells unlike non-sufferers. But why is that so? Today I am going to answer your question.
First of all lets go to the root of the problem which is the genetics (remember I have mentioned before that the disease is genetic?). There is one gene in your genome called the GAA gene which codes for the acid alpha-glucosidase enzyme. This is the enzyme which breaks down the glycogen by hydrolysing α-1,4- and α-1,6-glucosidic linkages in glycogen (don't worry if you don't understand this part! It just basically means the enzyme breaks these 2 types of bonds which holds the glycogen molecule together!). However for people with Pompe disease, there is a mutation in the GAA gene which cause a defect in the enzyme production, so no or very little acid alpha-glucosidase is produced.
Both glycogen and acid alpha-glucosidase are found in little packages in muscle cells called lysosomes. The job of alpha-glucosidase is to break down the glycogen in the lysosomes so that the glycogen will take up less space in the lysosomes. But if acid-alpha glucosidase is not present, the amount of glycogen will keep increasing in the lysosomes until the lysosome swells beyond the normal size. This can disrupt cellular functions in the muscle cells and the lysosomes can even burst, damaging the cell and the surrounding tissues. Ouch :(
(http://www.pompe.com/patients/about/cause.aspx)Here is a picture of what is going on inside a muscle cell of a person suffering from Pompe.
Myofibrils are structures found inside muscle cells that controls muscle contractions.
As you can see, glycogen can be found all over the muscle cell, interfering with the myofibrils and causing disruptions in the cell. This causes the symptoms of Pompe which includes muscle weakness and breathing difficulties (as respiration is controlled by muscles too).
(http://blogs.lt.vt.edu/joneill/2012/09/17/extraordinary-measures/)Since Pompe disease is genetic, it can be passed down from generations to generations. This disease is an autosomal recessive disease, meaning that you have to inherit the defective gene from BOTH parents to be affected. Or if only one of your parents carry the disease while your other parent is normal, you will be a carrier and you can pass down the defective gene to your children too. Sounds quite scary doesn't it :(
(http://www.pompe.com/patients/inheriting-pompe.aspx) Here is a chart showing how the inheritance of the disease works. Alleles basically means different forms of the same gene. In this case, there is the abnormal allele of the GAA gene which can cause Pompe disease and the normal allele of the GAA gene which won't cause Pompe disease.
*Do note that even though there are different type of Pompe disease (early-onset/late-onset), the basis behind the disease is the same.
Phew, that was lengthy wasn't it. The good news its that this is all we have for now! :D Time to give that brain of yours a break!
If you have any questions regarding what was mentioned in the posts (including this one) please feel free to comment below! We will try to answer your questions and maybe even discuss about it :)
See you next time!
~Mei Ying
References:
http://www.pompe.com/patients/about/cause.aspx
http://themedicalbiochemistrypage.org/pompedisease.php
http://www.pompe.com/patients/inheriting-pompe.aspx
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