#2 Zellweger Syndrome (ZS) is a serious condition marked by a variety of neurolo
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Question
#2 Zellweger Syndrome (ZS) is a serious condition marked by a variety of neurological symptoms. Although it is a “spectrum” disorder, with a range of severities documented, it is most often lethal in the first age of life. The cells of patients with ZS contain no or few peroxisomes.
A.) Find the symptoms and other features of ZS.
B.) Explain how a lack of functioning peroxisomes leads to the conditions described.
C.) Recently, it was found that the cause of ZS is almost always a mutation in one of the PEX genes. What are the PEX genes? List at least three of them and give the function, if known.
D.) How does mutation in a PEX gene lead to ZS?
Explanation / Answer
QA.) Find the symptoms and other features of ZS.
Zellweger syndrome is an autosomal recessive disorder caused by mutations in genes that encode peroxins, proteins required for the normal assembly of peroxisomes.
1. An enlarged liver; characteristic facial features such as a high forehead, underdeveloped eyebrow ridges, and wide-set eyes.
2. Neurological abnormalities such as cognitive impairment and seizures.
3. Infants will Zellweger syndrome also lack muscle tone, sometimes to the point of being unable to move, and may not be able to suck or swallow.
4. Some babies will be born with glaucoma, retinal degeneration, and impaired hearing. Jaundice and gastrointestinal bleeding also may occur.
5. Newborns may present with profound hypotonia (low muscle tone), seizures, apnea, and an inability to eat.
QB.) Explain how a lack of functioning peroxisomes leads to the conditions described.
Peroxisomes are cell structures that break down toxic substances and synthesize lipids (fatty acids. oils, and waxes) that are necessary for cell function. Peroxisomes are required for normal brain development and function and the formation of myelin, the whitish substance that coats nerve fibers. They are also required for normal eye, liver, kidney, and bone functions.
Zellweger spectrum disorders result from dysfunctional lipid metabolism, including the over accumulation of very long-chain fatty acids and phytanic acid and defects of bile acids and plasmalogens (specialized lipids found in cell membranes and myelin sheaths of nerve fibers).
QC.) Recently, it was found that the cause of ZS is almost always a mutation in one of the PEX genes. What are the PEX genes? List at least three of them and give the function, if known.
Mutations in the PEX1 gene are the most common cause of Zellweger spectrum disorder and are found in nearly 70 percent of affected individuals. The other genes associated with Zellweger spectrum disorder each account for a smaller percentage of cases of this condition.
PEX gene is one coding for a peroxin that is required for the formation, maintenance and proliferation of peroxisomes.
QD.) How does mutation in a PEX gene lead to ZS?
Mutations in at least 12 genes have been found to cause Zellweger spectrum disorder. These genes provide instructions for making a group of proteins known as peroxins, which are essential for the formation and normal functioning of cell structures called peroxisomes.
When mutation occurs on the genes the peroxins are not synthesized and peroxisome function will be impaired.
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