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HLTH101 Study Guide - Glucose-6-Phosphate Dehydrogenase Deficiency, Chemokine Receptor, Hemolytic Anemia

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Disease Resistance and Susceptibility Genes
o can confer an increase/decrease in susceptibility to a disease (they do not necessarily
cause the disease but they increase the chances of acquiring the disease).
o Or they influence the severity of the disease (do no cause the disease themselves).
Disease Restriction Genes:
Example Resistance to AIDS
Some people were at high risk of AIDS (i.e. prostitutes), but did not get infected - this did not
make sense.
Discovered that those individuals were homozygous for CCR5 (chemokine receptor 5)
Chemokine receptor 5 (if they were homozygous for this they seemed to remain unaffected).
Also found people who were positive for 10 years or more with no disease progression (had
minor symptoms but did develop bull-blown AIDS).
o Concluded that they were heterozygous for this mutation.
There are several alleles for this receptor (CCR5).
Receptor that allows AIDS into cell is CD4 receptor (receptor protein in T-cells).
o Receptor that seems to be responsible for transporting HIV into the cell.
CCR5 is co-receptor for CD4.
CCR5 also has to act for the CD4 receptor to work properly (they must work together).
T- cell will remain uninfected if the CCR5 receptor isn’t working.
If homozygous prevents development of AIDS/ heterozygous delays development of
Heterozygous Advantage
For recessive traits, must be homozygous to have the disease
Example of Malaria Resistance
Sickle cell disease if you’re homozygous, you have this disease. If heterozygous, you will
generally be healthy (although up to 40% of red bloods cell will be affected). Heterozygous
people will also be resistance to malaria.
Theory: infection reduces circulation of red blood cell, decreases oxygen partial pressure.
Sickling will then lead to destruction of infected red blood cells reduces ability to carry oxygen
- cells die.
Beta Thalassemia
Beta subunit of hemoglobin is affected - reduces synthesis of hemoglobin - less ability to
transport blood.
More severe than sickle cell…severe/lethal if you’re homozygous for disease.

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Heterozygous seem to be resistant to malaria.
Other examples:
Cystic fibrosis
o Being heterozygous gives protection against GI tract infection.
o As a result, this confers protection against diphtheria, cholera.
o Seems to give protection against cancer.
HTZ seemed to have reduced risk of miscarriage
And spontaneous abortions due to fungal infections.
Tay Sacks
o Allele confers resistance against tuberculosis (with one copy of allele).
Combine Susceptibility Resistance Genes
These are genes that reduce susceptibly of some illnesses but help us resist other types of ilnesses
Know what genetic influence is.
But if enzyme changes in some way, affects can vary according to environmental factors.
Most alleles don’t have single affect.
True for all genes?
Ex. G6PD deficiency
o One is deficient in this enzyme.
o 400 different alleles for this gene.
o Enzyme involved in glucose metabolism (RBC).
o If deficient in enzyme RBC will die Hemolytic anemia will develop (disease in which
RBC are being destroyed ).
o RBC can only be destroyed under certain circumstances.
o This pathology in which it destroys RBC occurs only under oxidative stress.
o So if one has this allele and this deficiency, its affects will not be noticed until RBC are
under oxidative stress where oxygen needs to be metabolized quickly.
o GENERALLY, in order for this to occur, certain environmental factors must be
present that will increase oxidative stress (these are called pro oxidants).
o Ex. of pro oxidants includes fava beans, moth bolls, sulfa drugs, antimalarial drugs all
these can lead to hemolytic crisis (if deficient in enzyme).
o Different from sickle cell/ thalassemia because it is x-linked thus, found predominantly
in males.
o Males - all cells will have it/ Females some cell will have it.
o Allele produces some resistance to malaria (deficiency can render the affects).
Deficiency affects internal environment of RB unfavorably.
Malaria part of its life cycle, the merozoids live in RBC, divide, and repeat
process in other RBC.
Since RBC environment is not favorable, merozoids die.
They will eventually adapt to environment, but delay development of malaria (if
RBC is affected by deficiency).
Resistance is less in males but if heterozygous (i.e. females), they will have more
resistance to malaria.
o A debate exists as to whether or not males are resistant to malaria:
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