BTEC 3301 Lecture Notes - Lecture 5: Chorionic Villus Sampling, Enzyme Replacement Therapy, Tay–Sachs Disease
4 May 2018
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Research Task 05
Tay - Sachs disease is commonly seen in children. It is rare and inherited and
destroys nerve cells in the brain and spinal cord. The process causes an infant to have a
slow development and muscle growth. This causes infants to lose the ability to turn over,
sit, and crawl. There is currently no cure to this disease, but there are ways for the
affected to be relieved from the pain.
This disease is a result from defects found in chromosome 15, the HEXA gene.
When normally working, the HEXA gene instructs the enzyme, beta-hexosaminidase A
to break down toxic substances. In this case, it breaks down a fatty substance called
CM2 ganglioside. Because of the mutation enzyme, gangliosides cannot be degraded
and continues to grow and destroy neurons. In the mutations, there can be synonymous,
where the nucleotide change doesn’t result in a protein change, and missense mutations,
where the mutation causes a change in the protein.
Any mutation change can be seen from TMHMM and signal peptides. The
normal results for the gene showed transmembrane between 1-25 amino acid. Signal
peptide is found at 1-22 amino acid. TMHMM results for the altered nucleotide showed a
transmembrane around 1-25 amino acid and the signal peptide showed results of
cleavage around 1-25 amino acids. These results showed that there are little to no
changes done in the synonymous mutations. This can also be seen in the dot plot which
was created to show 10 amino acids upstream and downstream of the mutation. Since
the mutation for the amino acid wasn’t changed, there was no gap shown in the dot plot.
However, if there were a missense change, there could be a change in the
transmembrane, the signal peptide would show a different cleavage, and there would
definitely be a gap in the dot plot sequence. This mutation can be seen as a structural
change since the protein is still the same. A functional change can be seen when the
protein does change. The mutation is found in the gene which encodes for the enzyme.
It could be a missense mutation or a synonymous mutation. A single mutation in the
DNA sequence can cause this change. Deletion of a nucleotide can also cause the
mutation to happen.
To identify Tay-Sachs disease and carriers, a blood test can be done to measure
the levels of Hex-A in the body. A DNA-based carrier test is also done to check for the
mutations that can be done to HEXA. Another test which can be done is the prenatal test,
which uses chorionic villi sampling, and amniocentesis. Those who have the disease
cannot be cured from this, but are treatments which are meant to alleviate the pain.
Research is being done to find out if enzyme replacement therapy can be used to work
on the disease. It works by replacing the enzyme with another enzyme or a synthetic
enzyme. There are also chaperone therapy which involves newly created
hexosaminidase A enzymes and guides them to the lysozyme to do its job. This is still
being researched and will take a long time before it will be effective. A drug called
pyrimethamine which increased hexosaminidase A activity. However, the patient that
took this drug showed no improvement in neurological or psychiatric symptoms.
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Document Summary
Tay - sachs disease is commonly seen in children. It is rare and inherited and destroys nerve cells in the brain and spinal cord. The process causes an infant to have a slow development and muscle growth. This causes infants to lose the ability to turn over, sit, and crawl. There is currently no cure to this disease, but there are ways for the affected to be relieved from the pain. This disease is a result from defects found in chromosome 15, the hexa gene. When normally working, the hexa gene instructs the enzyme, beta-hexosaminidase a to break down toxic substances. In this case, it breaks down a fatty substance called. Because of the mutation enzyme, gangliosides cannot be degraded and continues to grow and destroy neurons. In the mutations, there can be synonymous, where the nucleotide change doesn"t result in a protein change, and missense mutations, where the mutation causes a change in the protein.
