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SNP Basic Background information
We worked with the SNP rs333, which contains
32 nucleotides. The allele is positioned on
chromosome number 3 of the CCR5 gene and the
SNP is a frame shift mutation. The genotype for HIV
resistance for SNP rs333 is homozygous recessive.
Heterozygotes are partially resistant andhomozygote recessives are strongly resistant. The
most common genotype for the HIV resistance gene
is homozygous dominant with two copies of the
DNA code
GTCAGTATCAATTCTGGAAGAATTTCCAGACA. Thegenotype that contributes to the partial resistance
of HIV is one copy of the DNA code
GTCAGTATCAATTCTGGAAGAATTTCCAGACA.
Maximum resistance is present in human beings
with no copies of the DNA code.
This SNP slows down the progression of the HIV
infection disease. People that are heterozygous
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typically have lesser rates of HIV infection than
patients with the common allele of two copies of
the DNA code. Yet this doesnt necessarily meanthey prevent complete infection for the long term,
but rather simply slowing down the process for
heterozygotes. Homozygous are completely
immune to the infection.
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How does it prevent HIV?
During a typical HIV contraction, the CCR5
receptor acts as a target cell for infection. Located
on the helper T cells of CCR5 genes are specific
protein receptors called a chemokine receptors.
The HIV virus specifically binds to the external
proteins of the helper T cells, allowing HIV to enter
it via endocytosis.
Because of this, HIV resistance is distinguished
by the deletion of the 32 base pairs in the CCR5
gene. So, when a person is missing the 32 base pair
sequences, their helper T cells are absent of the
chemokine protein receptors. As a result, the HIV
virus cannot bind to and enter the helper T cells,
thus the infection is prevented.
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Occurrence Rate
CCR5 expression and presence is increased in
patients experiencing HIV infection. So by knowing
that HIV infection leads to a higher amount of CCR5
production than normal, we can measure the
expression of CCR5 and use it as an indicator for
ones HIV disease progression.
In an experiment done by the NCBI (National
Center for Biotechnology Information), individuals
from many different ethnic backgrounds were
tested for the rs333 mutation. Out of the 48
Africans and 46 Pacific islanders studied, none of
them had the beneficial mutation that prevented
HIV. Out of a group of 46 Hispanics, one person was
heterozygous for the rs333 mutation, and the rest
were normal. Out of 62 Caucasians, 6 were
heterozygous for the mutation, which means that
they have a lower chance of getting HIV, but none
were homozygous recessive.
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Pro/Con of rs333 SNP Awareness
There are a number of reasons why one wouldwant to know their rs333 SNP genotype. Most
importantly, this awareness could act as an
important step toward prevention. One would be
able to identify their risk of contracting HIV. This
could aid in minimizing or avoiding participation inactivities such as sexual intercourse or drugs. If
someone knew of their higher susceptibility, they
could choose not to have a child if their baby would
have a higher risk of developing AIDS.
In addition, knowledge about ones self could allow
others such as researchers and biologists practice
studies to further understand the rare condition. As
a result, they could become closer to developing a
cure for those that are also affected to benefit
everyone.
The rs333 SNP is present in people with
resistance to a fatal disease. Because of this rare
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benefit, almost everyone would want to find out if
they had the rs333 SNP.
Since the SNP is linked to a decreased risk of
type 1 diabetes and an abnormally excessive growth
of large blood vessels, genotype awareness could
help influence ones diet. By knowing one was at a
lower risk for diabetes, they might not fear the
disease and eat a sugar high diet. At the same time,
learning that ones blood vessels expand beyond
normal size, they could seek medical treatment
before the trait develops into a problem. For these
reasons, most people would want to know if they
had the rs333 SNP.
One would not be worried of carrying the rs333
SNP. Unlike damaging and fatal traits such as
malaria or AIDS, this trait is not a sensitive one to
discuss about because it codes for a advantageous
frameshift mutation that prevents a person from
contracting HIV.