Genetics - Gene Testing and Editing

What are diagnostic tests?

Laboratory tests that assist in the diagnosis of a specific disease. EX: prenatal tests

What are carrier tests?

Identify patients who carry mutations. EX: pre-implantation tests

What is the rationale for genetic testing?

To identify genetic disorders and assess risk for inherited conditions.

What is Factor V Leiden?

A blood clotting disorder caused by a mutation in the F5 gene.

What does the F5 gene do?

Provides instruction for making a protein called coagulation factor V.

What role does coagulation factor V play in the body?

It is crucial for the coagulation system, helping to form blood clots in response to injury.

How does Factor V Leiden affect blood clotting?

It prevents inactivation by activated protein C (APC), leading to increased clotting risk. APC normally inactivates coagulation factor V.

What is the inheritance pattern of Factor V Leiden?

Autosomal dominant with incomplete penetrance.

Major allele is GG; heterozygotes are AG, homozygotes are AA

How do the inherited alleles of Factor V Leiden impact pregnancy?

If one "G" and one "A" is inherited, it is associated with a 2- to 3X increase in relative risk for pregnancy loss, and possibly other pregnancy complications such as preeclampsia, fetal growth retardation, and placental abruption

What is the risk of DVT for heterozygotes of Factor V Leiden?

3-8x higher than the general population. About 1/20-1/50 Americans.

What is the risk of DVT for homozygotes of Factor V Leiden?

30-140x higher than the general populations. About 1/200 Americans.

What are some risk factors that may increase overall risk with Factor V Leiden?

Oral contraceptives, selective estrogen receptor modulators, pregnancy, smoking, immobility, long car rides, bedrest, surgery, and obesity.

What are some other examples of single gene defects for which genetic tests are available?

Marfan Syndrome, Achondroplasia, Fragile-X

What genetic condition is associated with the FBN1 gene?

Marfan syndrome.

What is achondroplasia?

Most common type of dwarfism. 99% of patients have a FGFR3 gene point mutation.

What is Fragile-X?

Mutation of FMR1 gene; nucleotide repeats causes loss of function of gene.

What is predictive testing?

Indicated when there is a positive family history, and an individual wants to understand his or her risk. Especially indicated when family members were diagnosed at early age. EX: Huntington's Disease, Breast Cancer, Alzheimers

What is the importance of early family history in predictive genetic testing?

It indicates a higher risk for genetic conditions and guides testing decisions.

What are the BRCA1 and BRCA2 genes?

Genes that produce tumor suppressor proteins, that when functioning as programmed repair damaged DNA. When mutation is present in one or both of these genes, damaged cells are able to continue to grow. Associated with breast cancer.

Who are candidates for carrier screening?

Those with a family history for a recessive condition, ancestral background, and standard of care perhaps.

EX: very important to predict Sickle Cell Anemia

What gene is associated with Sickle Cell Anemia?

The HBB gene. A point mutation leading to an amino acid change. HBB becomes what we label as the HBs gene. Stem cell research has been successful in mice models

What is the impact of the HBB gene mutation in Sickle Cell Anemia?

It leads to an amino acid change that affects hemoglobin function.

What is currently recommended for prenatal screening?

The PENTA test, sometimes called the Multiple Marker Screen. We have gone from 2 tests to 4 to now 5. Key to predict is Down Syndrome, Open Neural Tube Defects, and Trisomy 18 (Edwards syndrome).

What is the purpose of non-invasive prenatal testing (NIPT)?

To analyze fetal cell-free DNA for genetic abnormalities.

What do scientists look for in fetal cell-free nucleic acids during NIPT?

-Intact fetal cells: not as reliable, extremely rare & may persist for years

-Fetal "cell-free" nucleic acids (DNA and RNA): more plentiful and unique to the current pregnancy

Where do fetal cell-free nucleic acids come from?

-Baby via apoptosis of placental cells

-Mom via hematopoietic cell

When can NIPT be performed during pregnancy?

As early as 9-10 weeks gestation.

What are some conditions screened for by NIPT?

Trisomies, microdeletions, and fetal sex chromosomes.

What is the chance of having a child with a chromosome abnormality as maternal age increases?

The chance increases with age, from 1 in 525 at age 20 to 1 in 20 at age 45.

What is newborn screening?

A public health program to identify newborns at high risk for inherited disorders. Varies by country, and varies by state in the US.

What is the Recommended Uniform Screening Panel (RUSP)?

A list of conditions that newborns are screened for in the U.S.

What is the typical method for newborn screening?

A heel stick test performed 24-48 hours after birth.

How many conditions are currently screened in Pennsylvania?

99 conditions. Includes PKU, MSUD, Hb, CH, CAH, and GAL.

What is Phenylketonuria (PKU)?

A genetic disorder that results in the inability to metabolize phenylalanine, leading to brain damage if untreated.

What is Maple Syrup Urine Disease (MSUD)?

A metabolic disorder characterized by the inability to break down certain amino acids, leading to a sweet-smelling urine. Issue is PA the effects about 1/170 Amish children.

What is Congenital Hypothyroidism (CH)?

A condition present at birth that results in an underactive thyroid gland.

What is Congenital Adrenal Hyperplasia (CAH)?

A group of genetic disorders affecting the adrenal glands, leading to hormone imbalances.

What is Galactosemia (GAL)?

A genetic disorder that affects the body's ability to process galactose, a sugar found in milk.

What is Preimplantation Genetic Diagnosis (PGD)?

A technique used to identify genetic defects in embryos created through in vitro fertilization before implantation.

What is the steps in performing PGD?

-Treat woman with fertility drug, most are recombinant.

-Retrieve eggs from ovary and incubate with sperm.

-Fertilized eggs begin to divide into embryos.

-Perform PGD by removing a cell(s) from each embryo and test each for a predetermined genetic abnormality (or gender).

What is gene therapy?

A technique that modifies a person's genes to treat or prevent disease.

What type of gene therapy is primarily focused on?

Somatic gene therapy, which corrects only the affected cells and is not inherited.

What are some challenges with gene therapy?

-Need knowledge of defect & how it causes the disease.

-Need an animal model.

-Need a way of introducing the genetically modified cells or the normal gene into the body.

-Currently used for conditions with no alternative therapies.

-Must be safe.

What is In Vivo Gene Therapy?

The replacement gene is introduced directly into the body via a gene vector or virus

What is Ex Vivo Gene Therapy?

The removal, genetic alteration, and reinsertion of stem cells from a patient

What are some potential anatomical sites for gene therapy?

-Endothelium that form capillaries: can be genetically altered to secrete a variety of proteins into circulation.

-Immature muscle cells: dystrophin gene can be delivered to treat muscular dystrophy.

-Liver cells: can be genetically altered to treat inborn errors of metabolism.

-Lungs: can be treated with aerosol spray to treat conditions such a cystic fibrosis.

What is Severe Combined Immunodeficiency (SCID)?

A group of rare disorders caused by mutations in different genes involved in the development and function of infection-fighting immune cells. Now SCID is part of newborn screening to detect SCID before it symptoms begin.

Who does SCID impact?

Infants with SCID appear healthy at birth but are highly susceptible to severe infections. The majority (>80%) of SCID infants do not have a family history of the condition. However, X-SCID is a rare X-linked member of this group.

Who was the first gene therapy patient?

Ashanthi DeSilva, who received treatment for SCID due to ADA deficiency.

What are some challenges associated with gene therapy?

Determining which cells to treat, potential immune reactions, and ensuring effective gene expression.

What is CRISPR-Cas9?

A gene-editing technology that allows for precise modifications to DNA.

What is the purpose of the CRISPR on-off switch?

To control gene expression without altering the underlying DNA sequence.

What is antisense therapy?

A treatment that uses oligonucleotides to bind to mRNA and inhibit the expression of a gene.

What is ribozyme therapy?

A method that involves genetically modifying ribozymes to cleave mRNA and inhibit gene expression.

What does RNA interference (RNAi) do?

It regulates gene expression post-transcriptionally and has therapeutic implications.

What is the significance of gene-blocking therapies?

They can treat gain-of-function or dominant-negative mutations by inhibiting the expression of harmful genes.