Genetic Disorders and

Gene Therapy

Overview of Lesson• Genetic diseases

–Chromosomal–Single gene

• Gene Therapy– What is it?– How is it done?

Chromosomal Diseases• Gametes have abnormal

chromosome numbers and mutations

• Offspring inherit extra chromosome or are missing a chromosome

• Caused by problems with meiosis

Based on: Brooks/Cole – Thomson Learning

Nondisjunction of chromosomes during meiosis

Characteristics of a child with Down Syndrome-wide, rounded face -equal length fingers-Lower cognitive ability -webbed neck-enlarged tongue

Normal female karyotype with 46 chromosomes

Down syndrome karyotype with an extra chromosome 21

Based on: Mader, S., Inquiry Into Life, McGraw-Hill

Overview of Lesson• Genetic diseases

–Chromosomal–Single gene

• Gene Therapy– Process– Vectors

Important Points about Inheritance

•Genes have different forms, called alleles

•Each trait is controlled by effects of two alleles

•Some alleles are:• dominant/recessive • other alleles are co-dominant

•Allele for Widow’s Peak is dominant•A person with WW or Ww will have Widow’s Peak

•Allele for Straight Hairline is recessive•A person with ww will have a Straight Hairline

http://images.google.com/

Hairline Traits

Genotype vs. Phenotype

•Genotype refers to the alleles

•Phenotype refers to the appearance

Example: Genotype - PhenotypeWW - person has a widow’s peakWw - person has a widow’s peakww - person has a straight hair line

Genetics & Human Diseases• About 4,000 human diseases are

thought to be inherited.• Scientists are making good

progress figuring out where genes are located on chromosomes.

• Genetic diseases are caused by mutations, or incorrect sequences, in the normal form of the gene.

Huntington’s Disease

• Results in a loss of muscle control and mental function.

• The symptoms usually do not appear until after 30 years old.

• 1 in 10,000 people.

Caused by a dominant allele

Mucus in bronchi is thick, interfering with lung function

1 in 25 are carriers

One of the first disorders to be actively studied for gene therapy.

Most lethal autosomal recessive disorder in U.S.

Cystic Fibrosis

Based on: Harvard Family Health Guide, 1999

Sickle Cell Disease- recessive allele•Red blood cells are sickle shaped, issues with circulation causing anemia and pain

Sickle cell disease (sickle cell anemia)

• Codominant disorder found in African Americans.– 1 in 400 African Americans

• Can be fatal.• Possible cure: bone-marrow

transplants• The sickle cell trait can prevent

Malaria

Hemophilia• A disorder in which

a person’s blood does not clot properly.

• It is a recessive sex-linked, X-chromosome disorder.

• 1 in 10,000 males born are afflicted.

“Royalty Disease”

ADA-deficient persons are affected by severe immunodeficiency, with recurrent infections that might be life-threatening.

First disease approved for gene therapy.

Autosomal recessive disorder.

The drug exists but is very expensive, needs to be injected in vein for life.

Adenoside Deaminase (ADA) Deficiency

Overview of Lesson• Genetic diseases

–Chromosomal–Single gene

• Gene Therapy– What is it?– How is it done?

What is Gene Therapy?• Gene therapy is a

treatment or cure for disorders caused by mutated genes.

• It involves adding a normally functioning copy of the gene(s) to enough affected cells to restore normal function.

What is Gene Therapy

• Germline gene therapy would be the permanent transfer of a gene into sperm or egg cells.– Future generations would be “cured”.

• Somatic cell (body cell) gene therapy is ideally only the transfer of genes to the affected cells.

Gene Therapy Successes

• Although no gene therapies have been approved by the FDA for sale, some diseases have been experimentally successful:– Melanoma (skin cancer)– Severe Combined Immunodeficiencies– Hereditary Blindness– Sickle Cell Anemia

How is it done?

Functional proteins are created from the therapeutic gene causing the cell to return to a normal state.

Viral Vector Carrying Healthy Gene

Cell with mutated gene(s)

Vector inserts healthy gene into

cell

New gene in the cell along with original genes

Gene Therapy

To design and carry out a gene therapy treatment, a researcher must:

1. Identify the gene(s) responsible for the disorder.

2. Make copies of the normal gene. 3. Insert the copies into vectors. 4. “Infect” the affected cells with the vectors.5. Activate the gene so that transcription and

translation take place.

Viruses as Vectors• Replicate by inserting their DNA into

a host cell• Gene therapy can use this to insert

genes that encode for a desired protein to create the desired trait

• Four different types– Adenovirus– Adeno-Associated Virus (AAV)– Retrovirus– Herpes Simplex Virus (HSV)

Vector Advantages and Disadvantages• Adenovirus

+ Infects many cell types− Does not integrate into host genome and can be lost.

• Retrovirus+ Integrates into host genome and cannot be lost− Integrates into host genome and can cause cancer

• Adeno-Associated Virus (AAV)+ Integrates into host genome and cannot be lost− Difficult to work with.

• Herpes Simplex Virus (HSV)+ DNA stays in nucleus without integrating into host

genome.− Only infects cells of the nervous system.

Gene Therapy Disappointments

• In 1999 a boy died due to an immune response to an adenovirus gene therapy vector.

• Four children have developed cancer due to a retrovirus gene therapy vector

My Research: Building a better Vector

Adenovirus shell delivers genes

HSV-like virus protein tethers DNA to chromosome to keep genes in cell without integration

Your Goals:• Learn more about gene therapy by

completing a becoming a SPACE DOCTOR!

• Gene Therapy Vector Engineering Project.– First groups to complete the Space Doctor

activity gets to chose from the genetic diseases we talked about today.

– Use what you have learned and the Vector Toolbox to choose the best vector for treating the disease.

Tomorrow

• Learn about the techniques used to genetically engineer gene therapy vectors.

• Gene Therapy Vector Engineering Project.– Use paper models to simulate the

process of engineering your gene therapy vector.