The Genetic Basics: What Are Genes and What Do They Do?
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Play a Game: Which is a Genetic Disease? Diseases are caused by a variety of things such as bacteria or viruses. A genetic disease is caused by changes, or mutations, in a person’s DNA. Guess which of these is a genetic disease and click on the "answer" links to see if you are right.

 

(1) The Flu
(2) Bubonic Plague
(3) Rickets

(4) Heart Disease
(5) Muscular Dystrophy

Sickle Cell Anemia:
The first molecular look at a genetic disease
The genetic disease called sickle cell anemia causes red blood cells to become malformed. These sickle-shaped red blood cells may clog small blood vessels, and stop other red blood cells from delivering oxygen to the body. A blockage causes severe pain and damages organs and tissues by starving them of oxygen. Sickle cell anemia mainly affects people of Mediterranean and African descent. Red blood cells are round when they are carrying oxygen, but become sickle-shaped without oxygen. In 1949, Dr. Linus Pauling’s group at the California Institute of Technology found that the mutant sickle hemoglobin molecule had an electrical charge different from normal hemoglobin. Dr. Vernon Ingram (Massachusetts Institute of Technology) discovered why in 1956. The amino acid valine had replaced glutamic acid in each of two places on the mutant hemoglobin molecule.  

Normal and sickled red blood cells - Courtesy of Dr. Alan N. Schechter, National Institute of Diabetes and Digestive and Kidney Diseases

Normal and sickled red blood cells. Courtesy of Dr. Alan N. Schechter, National Institute of Diabetes and Digestive and Kidney Diseases
Heredity diagram: 
Here are four patterns of how the sickle cell allele might be inherited
Sickle cell-A: 
Two Parents Carrying the sickle cell trait
 
Sickle cell-B:
 
One parent carrying the sickle cell trait
 
Sickle cell-C:
One parent with sickle cell anemia

 

 
Sickle cell-D:
One parent with sickle cell anemia; one parent carrying the trait
In 1949, Drs. James Neel (University of Michigan) and E.A. Beet independently discovered that the mutation leading to sickle cell anemia acts genetically as a recessive trait.

Hydroxyurea
a drug that activates a gene:


Sickle cell anemia may be treated, but not cured, with a drug called hydroxyurea. A clinical trial to test this drug on humans finished early because the drug reduced patients’ pain episodes and need for blood tranfusions by about 50%. The drug is thought to activate a gene that produces fetal hemoglobin, which dilutes the sickle hemoglobin. Scientists now need to study how much of the drug patients should take, the drug’s long-term effects, and how safe the drug is for children and pregnant women to use.Treatment with hydroxyurea increases fetal-type hemoglobin (HbF) and lowers the abnormal sickle hemoglobin (HbS). HbF and the hybrid hemoglobin molecule of part HbS and part HbF do not stick together and are able to reduce the amount of HbS in the red blood cells and improve their flow.
 
Sickled cell blockage. Courtesy of Dr. Alan N. Schechter, National Institute of Diabetes and Digestive and Kidney Diseases
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Revolution in Progress: Human Genetics and Medical Research/

National Institutes of Health