Genetics and After Midterm Flashcards

Question

Aneuploidy

Answer 1

of chromosomes is not an exact multiple of the haploid set (related to increasing maternal age)

Answer 2

Monosomy – loss of a single chromosome from a diploid genome (2n - 1 chromosomes)

Answer 3

gain of one chromosome from a diploid genome (2n + 1 total chromosomes)

Answer 4

of chromosomes is exact multiple of the haploid set | humans are euploidy

Answer 5

more than 2 complete sets of chromosomes

Answer 6

one extra complete set of chromosomes (3n)

Answer 7

2 extra complete sets of chromosomes (4n)

Answer 8

Nondisjunction = cell division error in which homologous chromosomes fail to separate during segregation in meiosis I or the sister chromatids of a chromosome fail to separate during meiosis II or mitosis Consequence of nondisjunction: imbalance in the number of chromosomes, one daughter cell has two chromosomes or two chromatids, and the other has none

Answer 9

presence of different chromosome constitution (karyotype) within cells of a single individual condition in which a tissue may contain cells that have some chromosome abnormality and other cells with normal karyotype females are naturally mosaics for genes on the X chromosome because one X chromosome (paternal or maternal) in every cell is randomly inactivated (Barr body). Therefore, some cells express maternally-derived and others paternally-derived alleles

Answer 10

Sex chromosome abnormalities Autosomal (non sex-linked) chromosome abnormalities

Answer 11

XO – Turner’s Syndrome (45 chromosomes, missing one X) CLASSIFIED AS FEMALE Most XO fetuses die before birth Surviving individuals are females – 1 in 5,000 female births noticeable at puberty, when secondary sexual characteristics fail to develop ``` immature ovaries- sterile poorly developed breasts short stature webbed necks heart problems retardation unaffected lifespan ```

Answer 12

(XXY, 47 chromosomes) CLASSIFIED AS MALE ``` Male – incidence 1 in 1,000 male births Small testes, low testosterone - sterile Breast development in about 50% of XXY individuals Sparse facial hair Subnormal intelligence in some cases 48, XXXY 49, XXXXY ```

Answer 13

Jacobs Syndrome (XYY) Male – 1 in 1,000 male births Excessively tall sometimes retardation – not severe usually fertile but sometimes fertility affected antisocial behavior patterns e.g. sociopathic, aggressiveness

Answer 14

``` Females – 1 in 1,500 female births usually normal underdeveloped secondary sex characteristics sterility mental retardation ```

Answer 15

Monosomies – loss of one chromosome (2n - 1) – lethal Trisomies – addition of an extra chromosome (2n + 1): Down Syndrome – Trisomy 21 Patau Syndrome – Trisomy 13 Edwards Syndrome – Trisomy 18

Answer 16

Caused by an extra chromosome 21 (trisomy 21); nondisjunction in meiosis I; father contributing extra chromosome in 15% of cases The incidence of trisomy 21 is about 1 in 800 live births but SHARPLY INCREASES WITH MATERNAL AGE

Answer 17

Trisomy 13 Incidence 1 in 15,000 live births; maternal disjunction 50% of these babies die within the first month, 90% die within the first year, and very few survive beyond the first year ``` multiple dysmorphic features: Small head Small or missing eyes Cleft lip/palate Extra fingers Heart defects Abnormal genitalia Severe developmental and mental retardation ```

Answer 18

Trisomy 18 90% die within the first year, and very few survive beyond the first year The surviving individuals have severe mental and developmental retardation Small face Small sternum *********Clenched fingers and toes********

Answer 19

``` Due to break(s) along the axis of a chromosome Deletion Duplication Inversion Translocation (Transposition) Unilateral Reciprocal Robertsonian Translocation ```

Answer 20

A chromosomal deletion occurs when a chromosome breaks and a fragment is lost. This chromosome will be missing certain genes (can be a terminal deletion or an internal deletion; ABCDEF >> ABCEF or ABC/ Deletion Example: Cri du Chat Syndrome (46, 5p) length of short arm of chromosome 5 deleted varies: longer deletions = greater impact

Answer 21

A duplication occurs when a chromosome fragment becomes attached as an extra segment to a sister chromatid and thus it is present more than once in the genome It is usually caused by unequal crossing over between synapsed chromosomes during meiosis or through a replication error prior to meiosis ex) ABCDEF >>> ABCBCBCDEF Examples: Bar-eyed Drosophila- Instead of normal oval-eye shape, narrow slit-like eyes Charcot-Marie-Tooth disease in humans – neurological disease, chromosome 17 duplication

Answer 22

An inversion occurs when a piece of chromosome has been lifted out, turned around and reinserted. Thus a chromosomal fragment reattaches to the original chromosome but in the reverse orientation No loss of genetic information If the rearranged chromosome segment includes the centromere then the inversion is termed pericentric If it excludes the centromere then it is a paracentric inversion ABCDEF >> ADCBEF Individuals with one copy of a normal chromosome and one copy of an inverted chromosome are called inversion heterozygotes For 2 such chromosomes to pair properly during meiosis I, an INVERSION LOOP is formed The homologs will segregate resulting in 2 normal and 2 inverted chromatids Inversions, unlike the other structural chromosomal abnormalities, do not affect gene dosage.

Answer 23

the movement of a chromosomal segment to a new location in the genome A translocation can be UNILATERAL in which a section of a chromosome breaks off and is inserted into the end of another chromosome (either homologous or non-homologous)

Answer 24

exchange of segments between 2 non-homologous chromosomes (when a portion of one chromosome is transferred to another chromosome) Usually generate so-called "balanced translocations" In balanced translocations, there is NO NET GAIN OR LOSS of chromosomal material, just rearrangement of genetic material Usually without phenotypic consequences

Answer 25

Reciprocal Translocation with phenotypic consequences; Philadelphia chromosome = translocation between chr. 9 and chr. 22 leading to chronic myeloid leukemia altered chromosome 22 is called Philadelphia

Answer 26

translocation between chr. 8 and chr. 2, 14 or 22

Answer 27

Individuals carrying translocations have a greater risk of producing gametes with unbalanced combinations of chromosomes This depends on the segregation pattern during meiosis I During meiosis I, homologous chromosomes synapse with each other For the translocated chromosome to synapse properly, a translocation cross is formed which contains 2 normal chromosomes and 2 with translocated parts

Answer 28

1. Alternate segregation - Chromosomes on opposite sides of the translocation cross segregate into the same cell - Leads to normal and balanced gametes - Both contain a complete set of genes and are thus viable 2. Adjacent-1 segregation - Adjacent non-homologous chromosomes segregate into the same cell - Leads to unbalanced gametes - Both have duplications and deletions leading to birth defects 3. Adjacent-2 segregation - Adjacent homologous chromosomes segregate into the same cell - Leads to unbalanced gametes - Both have duplications and deletions leading to birth defects

Answer 29

***Most common type of chromosomal rearrangement in humans*** This translocation occurs as such: Breaks occur at the extreme ends of the short arms of two non-homologous acrocentric chromosomes The small acentric fragments are lost The larger fragments fuse at their centromeric regions to form a single chromosome Example: Familial Down Syndrome

Answer 30

Caused by translocation between chromosomes 14 and 21 - the majority of chromosome 21 is attached to chromosome 14 Chance of the same parents having a second affected child is extremely low However, there are cases where the syndrome occurs in a much higher frequency over several generations and this is known as Familial Down Syndrome

Answer 31

``` Down Syndrome: Nondisjunction during meiosis 47: (+21) No association with prior pregnancy loss Older mother Very low recurrence rate ``` Robertsonian translocation 46: -14, +t(14;21) May be associated with prior pregnancy loss May be a younger mother Recurrence rate 10-15% if mom is translocation carrier; 1-2% if dad is translocation carrier

Answer 32

changes in the nucleotide sequence of genes that appear to have no known cause (accidental) Result from abnormalities in cellular/biological processes (ex. error in DNA rep.) Underlying cause originates within the cell The rate is exceedingly low and varies considerably between different organisms (even within the same species, the spontaneous mutation rate varies from gene to gene) Hot spots = specific bases or regions that are more likely to be the site of a mutation within a gene some genes have locations within the chromosome that make them more susceptible to mutation and some can be found within a single gene

Answer 33

Caused by mutagens: agents that have potential to damage DNA These can be chemical or physical agents (uv light, ionizing radiation, toxins)

Answer 34

Germ-line mutations are those that occur in a sperm or egg cell - transmitted Somatic mutations are those that occur in any cell in the body, except germ cells - not transmitted Autosomal mutations are those within genes located on the autosomes X-linked mutations are those within genes located on the X chromosome

Answer 35

In a population, the wild-type (normal) is the relatively prevalent genotype A forward mutation changes the wild-type genotype into some new variation A reverse mutation changes a mutant allele back to the wild-type It is also termed a reversion

Answer 36

Loss-of-function mutations: reduce/eliminate function of the gene product When result in complete loss of function – null mutation Gain-of-function mutations: result in a gene product with enhanced or new functions ex) hereditary pancreatitis: mutation results in activation of a digestive enzyme (trypsin) that is normally inactivated in the pancreas Sickle cell disease: mutation results in resistance to malaria (new function)

Answer 37

Change in the nucleotide sequence of a gene May only involve a single nucleotide Point mutation = a change of one base pair to another in a DNA molecule ``` Point Mutations may be: > Base Pair Substitutions - Silent - Missense – new protein (amino acid substitutions) - Nonsense – stop codon > Base Pair Inversions > Base Pair Insertions & Deletions - Frameshift Mutations - Triplet Repeats ```

Answer 38

Change in single base pair A transition is a change of a pyrimidine (C, T) to another pyrimidine or a purine (A, G) to another purine A transversion is a change of a pyrimidine to a purine or vice versa Transitions are more common than transversions These mutations affect protein synthesis. If one nucleotide of a DNA triplet is changed, the corresponding mRNA codon will also be altered, resulting in the creation of a new triplet that codes for a different amino acid and thus codes for a different protein

Answer 39

Silent mutations are those base substitutions that alter a codon but do not alter the amino acid sequence of the protein Example: a change from normal codon CTC to CTT still codes for the same amino acid (Glu) in the protein, and thus, there is no alteration in function

Answer 40

Base substitutions in which an amino acid change does occur due to altered codon Example: Normal CTC >> CAC leads to different amino acid (Glu >> Arg) in polypeptide, so different function Sickle Cell Anemia is the result of one nucleotide substitution - Glutamic Acid is replaced by Valine - in the hemoglobin gene

Answer 41

those base substitutions that change a normal codon to a stop codon (UAG, UAA, or UGA) resulting in the termination of translation of the protein

Answer 42

Mutations may also involve the insertion or deletion of one or more nucleotides at any point in the DNA sequence within the gene Example: AACGTCTGCAAAT >>> AACGTCTG AACGTCTGCAAAT >> AACGTCTGCAGAGACAAAT

Answer 43

When loss or addition of nucleotides occurs, there is a shift in the reading sequence (frame) of DNA during protein synthesis Change in the 3-letter codons - different amino acid sequence - completely different protein formed – frameshift mutation If one of the many altered triplets is UAA, UAG, or UGA (the translation termination codons; stop codons) at that point polypeptide synthesis is terminated Therefore, frameshift mutations can have severe consequences

Answer 44

may also occur in the DNA sequence and result in altered amino acid sequence

Answer 45

The term refers to the phenomenon that a tandem sequence of 3 nucleotides within a gene is repeated many times expanding the size of the gene In normal individuals, these sequences are transmitted from parent to offspring without mutation However, in persons with TNRE disorders, the length of a trinucleotide repeat is increased above a certain critical size The number of repeats continues to increase in future generations ***Occurs within the coding sequence of a gene:**** Trinucleotide repeats lead to increased presence of a particular amino acid (e.g. CAG expansion which codes for glutamine) The encoded protein will contain long tracks of this amino acid This causes the proteins to aggregate with each other; protein aggregates are usually toxic and implicated in many diseases ***Occurs in a noncoding region of a gene*** Trinucleotide repeats can become chemically modified and cause changes in RNA structure This can result in gene inactivation/silencing

Answer 46

Fragile X syndrome (CGG repeat - arginine) > X-linked dominant trait > When the number of repeats reaches over 230, the CGG regions of the gene become chemically modified (methylated) – causing inactivation of the gene and this part of the chromosome where this gene is located becomes susceptible to breakage. Huntington disease (HD) > Autosomal dominant neurodegenerative disorder (CAG repeat-glutamine; HTT gene) > 36-39 repeats: later onset of the disease/slower progression of symptoms; 40+ repeats seriously affected > affects normal protein expressed in the brain; increased number of repeats = altered protein = increased decay rate of certain types of neurons Myotonic muscular dystrophy > Autosomal dominant (CTG repeat – leucine; MDPK gene) > normal protein expressed in skeletal muscle; increased number of repeats = altered protein = muscle wasting

Answer 47

Chromosome disorders > Sex chromosome abnormalities > Autosomal chromosome abnormalities ``` Single – gene disorders > Autosomal Dominant > Autosomal Recessive > X-linked dominant > X-linked recessive ``` Multi-factorial disorders > Multiple genes > Environmental factors Mitochondrial DNA disorders > Damage to mitochondrial DNA

Answer 48

caused by an autosomal dominant allele often encode structural proteins both homozygotes and heterozygotes are affected either sex is affected, exhibit the trait in approximately equal proportion, and equally likely to transmit the trait to their offspring no skipping of generations: disease phenotype is usually seen in one generation after another – vertical transmission if an individual has the disease, one parent must also have it if neither parent has the trait, none of the children has it ``` offspring usually heterozygous for the dominant allele (inherited from one parent) 50% of children inherit it Examples: Huntington disease Familial hypercholesterolemia Von Hippel – Lindau disease Neurofibromatosis Marfan Syndrome ```

Answer 49

AUTOSOMAL DOMINANT (= subgroup of hyperlipoproteinemia) **most frequent Mendelian disorder - 1:500 mutation in gene encoding low-density lipoprotein (LDL; bad cholesterol) receptor high levels of LDL in blood because too little taken up by cells narrowing of arteries (atherosclerosis), heart attacks at young age heterozygotes 2-3× elevated plasma cholesterol level – heart attack by 40-50 homozygotes 5-10× elevated plasma cholesterol levels – heart attack as early as 5 years of age and before 20 and death likely by that age

Answer 50

AUTOSOMAL DOMINANT Rare mutation in VHL (tumor-suppressor gene) on chr. 3 growth of tumors in the body (e.g. CNS, brain, spinal cord, kidney) and formation of cysts in internal organs higher risk for renal cell carcinoma

Answer 51

AUTOSOMAL DOMINANT disorder of the nervous system mutation in NF1 or NF2 gene on chr. 17 affects how nerve cells form and grow causes tumors to grow on nerves/tan or dark spots on skin "elephant man"

Answer 52

AUTOSOMAL DOMINANT connective tissue disorder caused by mutation in fibrillin-1 gene on chr. 15 defect results in too much growth of the long bones of the body – arachnodactyly (spider-like fingers) risk for aortic aneurism due to stretching of the aorta

Answer 53

rare - disease occurs only when both recessive alleles are present females and males affected equally parents are usually normal / unaffected (heterozygotes) 25% of offspring of 2 heterozygous parents (carriers) will be affected often encode catalytic proteins nearly all inborn errors of metabolism are recessive onset is frequently early in life Examples: Sickle cell anemia Cystic Fibrosis Phenylketonuria (PKU) Tay-Sachs

Answer 54

Most common lethal genetic disorder AUTOSOMAL RECESSIVE Mutation in CFTR gene on chromosome 7 1 in 25 Caucasian Americans is a carrier Thick mucus builds up in lungs and digestive tract Difficulty breathing & lung infections, pneumonia, bronchitis Death by lung complications – average lifespan 37 years

Answer 55

AUTOSOMAL RECESSIVE Can’t break down amino acid phenylalanine (missing critical enzyme) Phenylalanine builds up and interferes with nervous system leading to mental retardation (IQ below 50) and even death Early screening >> phenylalanine restricted diet for children with disorder

Answer 56

AUTOSOMAL RECESSIVE Lethal disease of the nervous system Mutation in HEXA gene on chr.15 encoding hexosaminidase (enzyme that breaks down a fatty substance found in nerve tissue called ganglioside) Fatty substance builds up in neurons Newborns appear normal first few months; gradual paralysis and loss of nervous function, mental retardation, blindness by age 4-5 – no cure Heterozygote carriers do not have disorder, but are protected from tuberculosis – mechanism unknown more prevalent in Ashkenazi Jews (1 in 30)

Answer 57

X-LINKED RECESSIVE G6PD = critical enzyme for preventing free radical damage in RBCs Converts glucose to ribose - NADPH production NADPH prevents building up of free radicals within cells G6PD deficiency can lead to rupture and break down of RBCs (hemolytic anemia) fava beans and napthalene contain compounds that produce free radicals G6PD deficiency = resistance to malaria Reason = malaria parasite infects mature RBCs and cannot survive in immature RBCs. In G6PD deficiency, RBCs are cleared rapidly before they mature, thus parasite dies as well 400 million people worldwide affected

Answer 58

X-LINKED RECESSIVE Caused by a mutation in the dystrophin gene, an important structural component within muscle tissue both sexes can carry the mutation, but females rarely exhibit signs of the disease Affected individuals have learning difficulties and mental retardation Most importantly: they have muscle weakness leading to muscular deterioration which starts as early as 3-5 years of age ability to walk is lost by the age of 12 and have to use a wheelchair They rarely survive past 20; death from breathing difficulty and heart disease ***DUCHENNE = X-LINKED RECESSIVE DISORDER WHEREAS MYTONIC MUSCULAR DYSTROPHAGY IS AN AUTOSOMAL DOMINANT DISORDER CAUSED BY TRINUCLEOTIDE REPEATS***

Answer 59

Caused by combination of multiple genes and environmental factors (e.g. diet and lifestyle) which can directly influence the expression of the genes involved Examples: Heart disease Cancer

Answer 60

Human mitochondrial DNA (mtDNA): 37 genes (13 encode proteins, 2 rRNAs and 22 tRNAs) mtDNA is vulnerable to mutations because: > High concentration of highly mutagenic free radicals generated by cell respiration accumulate in such a confined space > Reduced ability to repair mtDNA damage than nuclear DNA > Inherited maternally: only mother contributes mitochondria during conception; mitochondria in sperm destroyed by the egg cell after fertilization (mature oocyte >100,000 mtDNA copies, sperm <1000) Either sex is affected

Answer 61

``` Decreased Penetrance Variable Expressivity Delayed Onset of Genetic Expression Genetic Anticipation Genomic Imprinting Germline Mosaicism ```

Answer 62

% of individuals that exhibit some degree of expression of a mutant genotype Reduced penetrance = an individual who has the genotype for a disease but not exhibit the disease phenotype at all, even though he or she can transmit the disease gene to the next generation Example: familial cancer syndromes; many people with a mutation in breast cancer genes BRCA1 and 2 will develop cancer during their lifetime, but some people will not Cause of reduced penetrance: combination of genetic, environmental, and lifestyle factors Challenging to predict who will develop the disease and the risk of transmitting it to future generations

Answer 63

Range of expression of mutant genotype Penetrance may be complete, but severity of disease can vary greatly Variable expressivity: range of signs and symptoms that can occur in different people with the same genetic condition Example: Marfan syndrome; although mutation in the same gene some people have only mild symptoms (tall and thin with long, slender fingers), while others experience life-threatening complications involving the heart and blood vessels Cause of variable expressivity: combination of gene interactions, environmental, and lifestyle factors

Answer 64

many inherited disorders are not manifested until after birth and even later in life thus not possible until later in life to determine whether an individual carries a mutation – delayed onset Can cause difficulty in deducing mode of inheritance Examples: Huntington's, Tay Sachs, Duchenne Muscular Dystrophy

Answer 65

The phenomenon whereby a genetic disorder exhibits a progressively earlier age of onset and an increased severity in each successive generation Anticipation is common in trinucleotide repeat disorders: Fragile X syndrome, Huntington disease, myotonic dystrophy They all have: variation in the severity of symptoms (mildly to severely affected and death) Correlation between increased severity and earlier onset with successive generations

Answer 66

the expression of a gene depends on whether it has been inherited from a male or a female parent and determines whether specific genes depending on their parental origin will be expressed or remain genetically silent Examples: Prader-Willi syndrome (PWS; results when paternal chr. is deleted) Angelman’s syndrome (AS; results when maternal chr. is deleted) Both caused by deletion of an identical region of chr. 15, different phenotypes: PWS: mental retardation, eating disorder, obesity, diabetes AS: mental retardation, involuntary muscle contraction, seizures Therefore: same region in chr. 15 is imprinted differently in male and female gametes

Answer 67

the therapeutic delivery of nucleic acid polymers into a patient's cells as a drug to treat disease Is an approach to treat diseases based on modifying the expression of a person’s genes toward a therapeutic goal. ▪ Therapeutic genes are usually deliberately carried into the patient through a vector that transports the genes into target cells. ▪ Is potentially more effective, long lasting than protein therapy***** gene delivery is much more controlled, sustaining, and therapeutically benign

Answer 68

• Replace a mutated inactive gene that causes disease with a healthy copy • Inactivate, “knock out,” or suppress expression of a mutated gene that is functioning improperly. Dominant negative, gain of function or overexpression mutations. 1. Target the mutated gene to make it inactive CRISPR/Cas9 2. Introduce silencing RNA that target the mRNA of the gene to block protein production (using interfering RNA which is naturally produced by the body and have it silence bad gene production) • Introduce a new gene into the body to help fight a disease (not a replacement of the bad gene, but a new gene that codes for like an "antigene") • Correct a defective gene sequence - gene editing CRISPR/Cas9

Answer 69

Fix a genetic defect 1. SCID - Severe Combined Immunodeficiency 2. Cystic fibrosis 3. Type 1 diabetes • Treat cancer 1. Introduce a gene into immune cells to make them fight the tumor. 2. Introduce a gene into tumors to make them die. • Treat an infectious disease such as HIV/AIDS 1. Introduce a gene into immune cells to make them fight HIV better. 2. Introduce a gene that makes cells resistant to infection 3. Knock out CCR5 - the coreceptor for HIV to make CD4 T cell uninfectible.

Answer 70

You may have to fix the gene in all the cells, if it’s a disease such as Huntington’s, an autosomal dominant disease, where the defective protein remains in cells - so just replace the defective gene with healthy ones in the cells of the body However, the gene product may be released from cells and affects other cells, such as Type 1 diabetes. In this case you only have to “fix” a sufficient number of cells to generate enough of the gene product to restore health. The cells may or may not survive the life span of the patient- you may need to keep injecting yourself since the cells won't stay alive *******Stem Cells******* You can replace the stem cells with genetically modified one so that they repopulate the body with healthy cells - blood cell diseases. Stem cell modification potentially lasts longer than somatic cell editing. Correcting immune system disorders is a likely use for this. Bone marrow stem cells could be modified and used in a bone marrow autologous transplant.

Answer 71

Contains a gene for a fluorescent protein in their germline Example: Zebrafish Added a gene for fluorescent protein, added a controlling promoter so that each cell of the body has this gene to express fluorescence, add UV light, and BAM! glowing fish!

Answer 72

Take a vector (some mode of transmission of the synthesized gene) and directly inject it into the individual where they find their target cells

Answer 73

Obtain host cells from individual (draw blood), purify them, and then combine with vector. Then, take the engineered cells containing the therapeutic gene and inject them back into the individual

Answer 74

Cationic Polymers - which bind directly to the negatively charged DNA and allow for it to diffuse across lipid mem. Lipids - which form a micelle around the DNA and fuses with lipid mem. to allow for DNA to enter cell Naked DNA- into muscle cells where myocytes take up DNA at useful rate ***None allow specific targeting to cells and are inefficient compared with viruses** Basically you just take DNA, mix it with the polymers or liposomes and wait a few min. Then you mix this with the cells and the DNA is delivered into the cells’ nuclei where transcription begins. Naked DNA can be injected into muscle tissue which takes it into the cells.

Answer 75

****Viruses are the most common way to deliver genes into the body***** Adenovirus (Ad) = High cytotoxicity/immunogenicity (problem is your body might have seen this virus already which means you will develop an immune response to it which 1) inactivates vector you're trying to use therapeutically and 2) you might add so much and the body produces such a strong immune response that it KILLS you..) Retrovirus = Integration into the genome and long-term gene expression; can cause cancer Lentivirus - form of a retrovirus = HIV-derived vectors “Lentivectors;" Don’t seem to cause cancer (can get into cells that are not proliferating) Adeno-associated virus(AAV) = Low toxicity/, low immunogenicity Gene insert must be short Problems with viral vectors – Viral vectors carry the risks of toxicity, inflammatory responses, and gene control and targeting issues

Answer 76

Ornithine transcarbamylase deficiency, an X-linked genetic disease of the liver, the symptoms of which include an inability to metabolize ammonia – a byproduct of protein breakdown. Entered a clinical trial at the University of Pennsylvania in 1999 usingadenoviral vectors to deliver a corrected gene. The vector triggered a cytokine storm and he died from multiple organ failure - the first death from human gene therapy. He probably had an earlier natural exposure to the virus used to develope the vector so that he made a memory response that was very strong when a lot of vector was injected into him. The team led by James Wilson was faulted for not following proper procedures: 1. Gelsinger’s ammonia levels were too high for inclusion in the study 2. Failure of the team to report two prior similar but nonfatal incidents in other patients 3. Failure to disclose similar incidents and death in monkey trials This incident set back human gene therapy for about a decade

Answer 77

1. Remove the viral genes required for continual virus replication 2. Remove any genes that are toxic 3. Inert the gene you want to express into the viral genome (needs to be short DNA) 4. Generate a stock of virus in the lab 5. Infect cells 6. Select for successfully infected cells that make the factor you want 7. Put the cells back into the patient Vectors that do not integrate their DNA into the cell’s chromosomes will only last for weeks or months. Retroviral vectors integrate into the cell DNA and will last for the life of the cells. However, cell’s protect themselves from retrovirus integration, and often shut down the inserted DNA through epigenetic silencing.

Answer 78

ADA deficiency was an ideal target for the first set of gene therapy trials for a number of reasons: • The effects of the disease are reversible and do not cause irreversible, long term damage in the individual. • The disease results from the loss of function of a single gene. It is much more difficult to treat multiple genetic defects. • The adenosine deaminase gene is very small and easy to manipulate in the laboratory. • The target cells for the therapy are stem cells for lymphocytes (white blood cells), that are accessible, easy to grow and easy to put back into the body of a patient. • Defect is autosomal recessive, so you don’t have to repair either or both genes, just put a new good gene into a cell to fix the problem. • You don’t have to replace all the defective cells, just a few is enough. • The alternative treatments are expensive and/or hazardous

Answer 79

Retroviruses can cause cancer by inserting near oncogenes and turning them on. However, a retrovirus therapy for ADA-SCID has not caused cancer in test and has recently been approved for use in Europe

Answer 80

(i) Collection of PBMC's and transfer to GMP manufacturing facility (ii) viral gene transfer of TCR or CAR into PBMCS (genetically modified cell) (iii) propagate gentitically modified tumour-reactive T cells (iv) transfer cells from manufacturing centre to patient (v) precondition patient (chemotherapy) and transfuse T-cell therapy

Answer 81

Bacteria have a defense mechanism against viruses that targets their DNA in a sequence-specific manner and cleaves it using the enzyme Cas9. This system has been modified to allow the targeting of any gene in animal genomes, allowing any gene to be disabled or edited. • Bad sequences can be corrected by editing or removal. • New DNA sequences can be inserted.

Answer 82

Bacteria have a defense mechanism against viruses that targets their DNA in a sequence-specific manner and cleaves it using the enzyme Cas9. This system has been modified to allow the targeting of any gene in animal genomes, allowing any gene to be disabled or edited. • Bad sequences can be corrected by editing or removal. • New DNA sequences can be inserted. A problem with CRISPR is that is has “off target” effects: Sometimes the wrong DNA target is modified

Genetics and After Midterm Flashcards

(106 cards)