Lecture 7: Molecular Detection of Inherited and Metabolic Diseases Flashcards
Type of mutations that are inherited from a parent and are present throughout a person’s life in virtually every cell in the body
Inherited (germ line)
-These mutations are also called germline mutations because they are present in the parent’s egg or sperm cells, which are also called germ cells.
Type of mutation that occurs at some time during a person’s life
-present in only certain cells, not in every cell in the body
-These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division
Acquired (somatic/sporatic)
-Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation
Types of mutations at the chromosome level
- Deletions
- Duplications
- Inversions
- Translocations t[#,#]
encodes a cytoplasmic tyrosine kinase
C-abl
promotes oligomerization
Bcr
promotes activation of
abl by oligomerization induced autophosphorylation
Bcr-abl fusion
What is the most common variant with Burkitts Lymphoma?
T(8;14)(q24;q32)
What is Burkitts lymphoma associated with?
the Epstein-Barr Virus
(EBV) in nearly 100% of cases in endemic form in central Africa.
* In the sporadic forms (occur in Western countries), EBV is present in approximately 30% of cases and in 40% of immunodeficiency-associated
cases
Burkitts Lymphoma T(8;14)(q24;q32):
______ is brought under the
transcriptional control of the IG enhancer elements leading to its constitutive transcriptional deregulation
MYC
Base substitutions (Point Mutation)
* ____________ (purine for purine, pyrimidine for pyrimidine)
* ____________ (purine for pyrimidine)
transition
transversion
Type of mutation:
amino acid Condon to “stop”
Nonsense mutations
What are the three stop codons?
UAA, UAG, UGA
A genetic variant which results in a shorter version of the protein being produced
Truncated protein
Example of nonsense mutation
Thalassemia
* beta-thalassemia in Sardinia, Codon 40, CAG (Gln) to TAG (stop), Mutation associated with Low LDL
* alpha-thalassemia: Constant Spring: from stop codon to glutamine @ 142 (TAA to CAA)
Multiple gene deletions also termed
CATCH 22
Multiple gene deletions:
What does CATCH 22 an acronym for?
Microdeletions in chromosomal region
22q11.2 (CATCH 22)
cardiac defect, abnormal
facies, T-cell deficit, cleft palate, and hypocalcemia.
What are two examples of multiple gene deletions?
-DiGeorge syndrome
-Velocardiofacial syndrome
Frame-Shift mutations are _____________, not multiple of 3bp
insertion/deletion
Examples of frame-shift mutations
e.g., Tay Sachs 4 bp insertion,
* BRCA1 185 delAG, BRCA2 6174delT, etc.
* Blood group O (1 bp deletion)
What are other types of mutations?
- Cap-site Mutants
- Mutations in initiation codons
- Creation of a new initiation codon
- Mutations in termination codons
- Polyadenylation/cleavage signal mutations.
Factor V Leiden Pathophysiology:
In the normal person, factor V functions as a cofactor to allow factor _____ to activate an enzyme called thrombin. Thrombin in turn cleaves
fibrinogen to form fibrin, which form the fibrin clot.
Xa
Factor V Leiden Pathophysiology:
Activated protein _______ is a natural anticoagulant that acts to limit the extent of clotting by cleaving and degrading factor V.
C (aPC)
Factor V Leiden Pathophysiology:
The excessive clotting that occurs in this disorder is almost always restricted to the…
veins, where the clotting may cause a deep vein
thrombosis (DVT)
How common is Factor V Leiden in Caucasians in North America?
5%
What causes increased clotting with Factor V Leiden?
protein C cannot inhibit factor 5 —> increased clotting
What is the inheritance type for Factor V Thrombophilia ?
autosomal dominant condition that exhibits
incomplete dominance
Factor V thrombophilia results in a factor V _____ that cannot be as easily degraded by activated protein C.
variant
What is the gene responsible for Factor V thrombophilia pathology?
What chromosome?
F5, single nucleotide polymorphism
Chromosome 1 in exon 10
-A single nucleotide polymorphism (SNP) located in exon 10.
FV Thrombophilia:
A missense substitution of base ________, changes the protein’s amino acid from arginine to ____________***
G1691A
glutamine (R506Q)
What is the result of the mutation seen with FV thrombophilia?
- deplete the protein C binding site in the Coag pathway
- removes a cleavage site of the restriction endonuclease MnlI
Factor V Leiden:
The mutation (a
1691G→A substitution)
removes a cleavage site
of the restriction
endonuclease _____
MnlI,
PCR products treat with MnlI
Unstable trinucleotide repeat examples
- Fragile X Syndrome (CGG)n 5’UT
- Huntington’s syndrome (CAG)n polyglutamine
- Myotonic dystrophy (CTG)n 3’UT
- SCA type 1 (CAG)n polyglutamine
- Friedrich’s Ataxia (GAA)n intron 1
The most common cause of inherited intellectual disability and the most
common known genetic cause of autism or autism spectrum disorders
Fragile X Syndrome
Fragile X syndrome occurs in approximately 1 in_______ males and 1 in ________
females.
4,000
8,000
Fragile X syndrome mutation is in the ______ gene
FMR1
-FMRP
What is the FMRP regulate?
the production of other proteins and plays a role in the development of synapses, which are specialized connections between nerve cells.
How is fragile X-CGG expansion mutations detected?
by PCR and Southern Blot
An autosomal dominant and almost fully penetrant inherited disorder with
progressive brain dysfunction that causes uncontrolled movements,
emotional problems, and loss of thinking ability (cognition).***
Huntington’s Disease
How prevalent is Huntington’s disease in people of European ancestry?
estimated 3 to 7 per 100,000 people
What is the mutation that causes Huntington’s disease?
CAG trinucleotide repeats in coding region**
The ______ gene product is called huntingtin protein.
HTT
Huntington’s Disease:
- An increase in the size of the CAG segment (>40) leads to the production of an
abnormally long version of the huntingtin protein. - The elongated protein is cut into smaller,______ fragments that bind together and accumulate in neurons, disrupting the normal functions of these cells
toxic
What does CFTR stand for?
Cystic Fibrosis Transmembrane
Conductance Regulator
Frequency of people who carry the CF gene is about…
- 1 in 29 Caucasian Americans;
- 1 in 46 Hispanic Americans;
- 1 in 65 African Americans; and
- 1 in 90 Asian Americans.
What are clinical features of cystic fibrosis?
Chronic Sinusitis, Pancreatic insufficiency (malnutrition), Airflow obstruction
Recurrent infection (Psa, S. aureus), Obstructive azoospermia (CBAVD)
What is the role of the CFTR protein?
To allow chloride ions to exit the mucus-producing cells.
* When the chloride ions leave these cells, water follows, thinning the mucus, allowing the mucus to be moved steadily along the passage ways to aid in cleansing.
in CF, the defective ______
protein does not allow chloride ions out of mucus-producing cells.
CFTR
The CF Gene: Vital Statistics
- Complete gene locus spans ____ kb
- ___ exons
- Mature mRNA of _______bases
250
27
6,500
CF Gene encodes an ion channel of _______ amino acids.
1,480
What is the inheritance pattern of CF?
autosomal recessive***
characterized primarily by progressive lung disease, pancreatic insufficiency, gastrointestinal obstruction and an excess of sodium and chloride in the sweat.
Cystic Fibrosis
A defect of _________ gene causes all the consequences of CF.
Over ________ known defects in the CFTR gene that can cause CF.
single
2,000
Cystic Fibrosis:
Three-nucleotide deletion of codon _______ in 70% patients
508 (phe)
Major Mutations of CF:
_______ mutation leads to improper processing and intracellular degradation of the CFTR protein.
Delta F(508)
Major Mutations of CF:
Other mutations in the CF gene produce fully processed CFTR proteins that are either ____________ or ___________.
non-functional or partially
functional
True or false:
The screening tests for CF is not done as part of the standard newborn screening
False.
part of standard newborn screening tests
Traditional Screen Test (IRT) for CF:
The screening test looks for elevated levels of a substance called _______________, which is an enzyme produced by the pancreas.
immunoreactive trypsinogen (IRT)
In people with cystic fibrosis (CF),___________ can block the pancreatic ducts that lead into the small intestine, preventing trypsinogen from reaching the intestine and preventing the breakdown of food proteins
mucous plugs
What is done if the Traditional Screen Test (IRT) for CF is positive?
a sweat chloride will be done
What is the gold standard for CF testing?
sweat chloride test, or sweat test
What does the sweat chloride test measure?
the amount of salt in a person’s sweat, which is higher than normal in people with CF.
What is considered positive for a sweat chloride test?
A chloride content greater than 60 mmol/liter***
Why would a doctor order a sweat chloride test when the IRT levels are elevated but no CFTR mutation was detected?
in case the baby
has one of the less common mutations that was not included in the genetic
testing panel.
What does ASO stand for?
Allele-Specific Oligonucleotide probes
ASO (n) probe =
ASO (x) probe =
WT (wild type)
mutant
Genetic Testing Complexities:
a single genetic mutation results in a range of phenotypes.
Variable expressivity
Genetic Testing Complexities:
the same phenotype results from mutations in different genes (includes diseases with multiple genetic components)
Genetic heterogeneity
Genetic Testing Complexities:
mutation is present without the predicted phenotype.
Penetrance
