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HLTH 101

Disease Resistance and Susceptibility Genes Introduction  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 symptoms. 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.  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. o PKU  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:  It is thought that they only have temporary relief.  Hypothesis: For females, the merozoids adapt to one particular type of RBC (specific type of oxygen environment in RBC). If they affect the other type, then they cannot survive.  So after the merozoids reproduce and leave, suppose you have half of RBC that have deficiency and the other half don’t, there is a 50/50 chance of going to a RBC that they can survive in and so on. Keeps # of merozoids under control.  Mutations reside in germ cells given to offspring during conception.  Many mutations won’t have a great affect on person (i.e. cell mutated to release toxins will not have huge affect – will only affect surrounding cells).  However, what if a mutation in a cell occurred to have the cells to keep on dividing (even when body reaches a point where cell division should stop)? o Cells become cancerous – only mutation that can affect health. Innate Factors in the Human Body and Health – Cancer  Cancer can stem from changes that occur in innate factors in our bodies.  Other words for cancer: Neoplasia, malignancy. Impact of Cancer  Stats Canada o Lifetime risk of cancer (incidence) : 40% women / 45% men. o 25% of all deaths – Cancer – Canada. o Incidence rates peak when one is in their 60’s. o Mortality peaks in 70’s or 80’s. o Second leading cause of death. o Before 75 – is first cause of death. Did we win war on cancer?  Problem is unique  Need to determine the size of the problem of cancer. o If size of problem can be determined, we can find out whether we are winning or losing war on cancer.  How to determine size of problem? 1. Determine incidence. o Lung cancer is declining (decrease in smoking).  Effects of diagnosis? (Publicity campaigns encouraged people to get screened)  These publicity campaigns could be one reason rates in cancer increases – bc more people went out and got screened. 2. Mortality rates: Use 5 – year survival rate, if you survive within those years, you’re considered cancer survivor.  Rate has been increasing since 1970’s  Why? o Due to early detection o Increased screening since 70’s – people getting diagnosed earlier.  Potential biases o Screening bias (do people who volunteer to get screened more healthy or interesting in their health?)
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