What is PMM2 Deficiency?





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Published on Feb 8, 2016


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Learn about the underlying biology of Congenital Disorders of Glycosylation (PMM2-CDG), what treatment options are available, and how you can make a difference to fill a very urgent gap.

This video was produced with support from the Amour Fund.

There are more than 20,000 genes in a single human cell. Mutations or changes in the DNA sequence of only 1 of these genes can have harmful consequences throughout the entire body. Today we’re going to talk about the PMM2 gene, the DNA sequence that produces the PMM2 protein.

A defective copy of the PMM2 gene is the most common cause of a disease called “congenital disorders of glycosylation” or “PMM2-CDG”. PMM2-CDG is the most common of a growing family of more than 100 extremely rare inherited metabolic disorders. Only about 1000 children and adults have been reported worldwide.

The PMM2 protein plays an important role in glycosylation, a complex process that adds sugars trees (glycans) to proteins inside cells. It helps to think of this complex process as an assembly line. The PMM2 protein is a builder robot that adds parts to other robots. When PMM2 robot is not working properly it forgets to add all the parts, which causes the robots produced in the assembly line to malfunction. Having the right parts is as important for robot function as having the right sugar trees is for regulating the activity and function of proteins, enzymes and hormones. In CDG patients, the sugar trees can be incomplete or absent altogether.

But why do people get PMM2-CDG? To understand this, it is important to remember that we carry 2 copies of every gene in our DNA, one copy from our mother and one from our father. If a child is affected with PMM2-CDG, both copies, one from the mother and one from the father must have alterations in the PMM2 gene. This is extremely rare!

However, if a person only received 1 altered copy, then they are a carrier, and not affected. When both parents are carriers, it would be expected that there is a 1 in 4 chance that their child will have CDG, and that 1 in 2 will be carriers. However, based on data from families with affected children, the risk is higher, about 1 in 3.

As we just mentioned, glycosylation occurs in all cells throughout the body, so having PMM2-CDG has harmful consequences throughout the body. Affected patients can develop neurological symptoms such as seizures, and stroke-like episodes. Symptoms resulting from a small cerebellum include impaired coordination, weak muscle tone, and eye movement problems. Most CDG patients use a wheelchair and have developmental delay. Other symptoms can include vomiting, failure to grow, liver problems, heart problems, kidney problems, hormone imbalance, immune deficiency, scoliosis and blood clotting issues.

PMM2-CDG is a spectrum disorder and symptoms differ in severity between individuals. Some patients may only have mild developmental delay while others have significant medical problems, typically starting in the first few months of life. About 20% of these infants don’t survive the first year of life.

Currently there is no cure for PMM2-CDG. Treatment involves management of the symptoms that are apparent in each individual, including Physical Therapy to improve core strength and mobility, Occupational Therapy for coordination, Speech Therapy for talking and eating.

Thanks to advances in the field of genetics, researchers have found the genes responsible for many diseases, including CDG. More research needs to be done to understand how impaired PMM2 leads to complex medical issues. Supporting research will ensure that a cure for CDG does not come too late.

This video has been produced by Youreka Science in collaboration with the Amour Fund. To support the Amour Fund and CDG research please make a contribution.


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