Lysosomal Storage Diseases: Mannosidosis

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  • 0:05 Breaking Down Sugar
  • 0:40 What Is Alpha-Mannosidosis?
  • 1:10 Why Does…
  • 2:51 Clinical Signs,…
  • 3:33 Treatment of…
  • 4:07 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

This lesson will discuss a lysosomal storage disease known as mannosidosis. We'll go over why it's called that, what it does to the body, and why it occurs. You'll also learn if there is a cure for this disorder.

Breaking Down Sugar

Sugar. It's found in candy, bread, fruits and vegetables, and much more. When it's processed and refined down to table sugar, we crave it like crazy. Your sense of taste isn't the only thing that craves sugar, however. Your entire body depends on sugar to drive its energy-making processes. But, too much sugar is a bad thing. It may cause cavities, diabetes, and obesity. Even your own body's cells may become obese, or swollen, due to a problem associated with the breakdown of sugar, as this lesson will point out.

What Is Alpha-Mannosidosis?

The condition that does this is a rare inherited disorder that causes intellectual disabilities, skeletal deformation, and affects the function and structure of internal organs. This condition is called alpha-mannosidosis. This is a rare disorder that affects about 1 in 500,000 people worldwide and has been linked to a genetic mutation in a gene called MAN2B1.

Why Does Alpha-Mannosidosis Occur?

The reason it is called alpha-mannosidosis is because a defect arises in a cellular protein called alpha-mannosidase. This protein is an enzyme, a type of molecule responsible for speeding up chemical reactions. Specifically, this enzyme breaks down complex sugar molecules within a cellular structure known as a lysosome. A lysosome is a structure that functions as the cell's digestive system.

If a genetic defect causes this enzyme to malfunction, the complex sugars containing a sugar molecule, called mannose, cannot be broken down. If they cannot be broken down, they accumulate and are stored within the cell as a result of the defect in the lysosome's enzymes. That's why any type of mannosidosis, including the even more rare beta-mannosidosis, is also known as a lysosomal storage disease. As these complex sugars accumulate within the cell, instead of being degraded and processed by the lysosome, they cause the cell to malfunction.

Imagine if you were to stuff yourself silly with sugary doughnuts. Your body's lysosome is like your stomach. If the acid, enzymes, and all sorts of other stuff responsible for digesting those doughnuts malfunctioned due to a genetic defect, the doughnuts would just sit there in your stomach and accumulate as you ate more and more of them. The accumulation of doughnuts in your stomach would cause you a lot of pain, may compress other vital organs in the area, causing their malfunction, and eventually may even burst and cause you to die. That's essentially kind of what happens within a cell with this storage disorder.

Clinical Signs, Symptoms, and Diagnostics

As the cells inside a person's body begin to malfunction due to alpha-mannosidosis, they obviously cannot do their job correctly, resulting in:

  • Intellectual disability
  • Skeletal malformations, such as thickening of the skull
  • Hepatomegaly, or the enlargement of the liver

The reason organs like your liver enlarge with this disease goes back to the whole doughnut and stomach example. The cells that make up your liver just become engorged with sugar they cannot process and therefore become swollen with it, leading to hepatomegaly. When suspected, this disease is diagnosed by testing the activity of alpha-mannosidase in leukocytes, or white blood cells.

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