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Biochemistry Block 4 > Single Gene Disorders > Flashcards

Single Gene Disorders Flashcards

1
Q

Explain the 2 general types of autosomal dominant disorders:

  1. Loss of function mutations - defects in what 2 things
  2. Gain of function mutations
A
  1. Structural proteins and regulatory proteins

2. Normal protein with toxic properties

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2
Q
  1. 2 examples of loss of function autosomal dominant diseases - defect in regulatory proteins
  2. 1 example of structural protein loss of function disease
  3. 1 example of gain of function autosomal dominant diseases
A
  1. Familial hypercholesterolemia and myotonic dystrophy
  2. Osteogenesis imperfecta
  3. Huntington disease
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3
Q

Neurofibromatosis type 1

  1. Type of disease
  2. Gene defect?
  3. Clinical presentation (4)
  4. Important genetic concept related to this disease?
A
  1. Autosomal dominant
  2. Mutation in cell cycle regulatory protein
  3. Cafe-au-lait spots, axillary freckling, neurofibromas, lisch nodules
  4. Variable expression - some in same family mildly/severely affected
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4
Q

Marfan syndrome:

  1. Type of disease
  2. Gene defect? What is the gene component of
  3. Clinical picture?
  4. Good example of pleiotropy - define
A
  1. Autosomal dominant
  2. Fibrillin gene - component of ECM and connective tissue
  3. Skeletal abnormalities, hypermobile joints, myopia and detached lens, aortic aneurysm
  4. Single mutation affects multiple organ systems
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5
Q

Thalassemias

  1. Type of disease
  2. Gene defect?
  3. Where in the world is it most frequent (3)
  4. What is adult hemoglobin (HbA) composed of?
  5. Humans have 2 copies of the beta globin gene on what chromosome? Alpha globin? How many copies of each?
  6. How is fetal hemoglobin (HbF) different
A
  1. Autosomal recessive
  2. Imbalance in globin chain synthesis
  3. Mediterranean sea, africa, and southeast asia
  4. 2 alpha and 2 beta chains
  5. Single gene on chromosome 11 for beta (so 2 copies total). 2 genes on chromosome 16 for alpha (so 4 copies total)
  6. Gamma chains replace beta chains
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6
Q

Explain each of the following types of thalassemia
1. Alpha? What accumulates?

  1. Beta? What accumulates?
A
  1. Results from insufficient synthesis of the alpha chain- beta chain accumulates
  2. Results from insufficient synthesis of the beta chain - alpha chain accumulates
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7
Q

Beta thalassemia:

  1. Alpha chain accumulates - are they soluble or insoluble?
  2. Fate of cells?
  3. Results in what condition
  4. How will lab results look?
A
  1. Very insoluble
  2. Premature death of cells
  3. Hemolytic anemia
  4. Low hemoglobin and excess alpha globin
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8
Q
  1. Beta thalassemia minor vs major
  2. What is B+? What is B0?
  3. What is thalassemia intermedia
A
  1. Minor= 1 normal and 1 mutant
    Major= 2 mutant copies
  2. B+= leads to reduced amounts
    B0= leads to total absence of functional B-globin
  3. B+/B+ or B0/B+
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9
Q
  1. Thalassemia minor may be mistaken for?

2. How is it diagnosed? (2)

A
  1. Iron-deficiency anemia

2. Hemoglobin electrophoresis or blood work

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10
Q
  1. Why do babies born with thalassemia major appear normal at first?
  2. How will these patients present? (4)
A
  1. Because babies have HbF, become anemic when B globin synthesis increases to get HbA
  2. Severe anemia, hepatosplenomegaly, skeletal deformities, systemic iron overload
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11
Q

Thalassemia major:

  1. What type of skeletal deformities will they show? Why?
  2. Systemic iron overload is due to what 3 things?
  3. Treatment for this condition
A
  1. Face/skull; due to bone marrow expansion (to increase RBC production)
  2. RBC turnover, increased iron absorption in diet, accumulation in liver and heart
  3. Regular blood transfusions with iron chelation therapy, bone marrow transplant (dangerous), potential gene therapy
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12
Q

Thalassemia intermedia:

1. Varies in severity, treatment?

A
  1. Blood transfusions are only required occasionally
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13
Q

Alpha thalassemia:

  1. What is the most frequent mutation?
  2. Normal genotype would be?
  3. Silent carrier?
  4. Alpha thalassemia trait
  5. HbH disease - clinically severe
  6. Hydrops fetalis - usually fatal at birth
A
  1. Deletion of the entire gene
  2. aa/aa
  3. -a/aa
  4. —/aa and -a/-a
  5. —/-a
  6. —/—
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14
Q
  1. Symptoms of silent carriers?
  2. Symptoms of a-thalassemia trait
  3. Symptoms of HbH disease
  4. If all 4 alpha genes are missing, what happens?
A
  1. Essentially normal - no RBC abnormality
  2. Same as those with beta thalassemia minor
  3. Same as those with beta thalassemia intermedia
  4. Usually lethal in utero or shortly after birth
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15
Q

What does the gamma globin form in cases of alpha thalassemia in utero/shortly after birth

A

Hemoglobin bart (Hb Bart)

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16
Q

Alpha thalassemia:

In patients with at least one copy of the alpha globin gene (surviving patients), what accumulates?

A

HbH

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17
Q

Compare HbH and Hb Bart to the aggregates seen in beta thalassemia

A

The ones in alpha thalassemia (HbH and Hb Bart) are more soluble and less toxic; less severe phenotype

18
Q

How often do the following need blood transfusions:

  1. Thalassemia major
  2. Thalassemia intermedia
A
  1. Once every 2-4 weeks

2. Only when needed (like during an infection)

19
Q

Males are considered __ when thjey have genes on the X chromosome, why?

Are phenotype issues more common in males or females for X linked diseases, why

A

Hemizygous; only have one X chromosome

Males because they only need 1 copy of a defective X to be phenotypic, females need 2

20
Q

Hemophilia A and B

  1. Type of disease
  2. Gene defect for both
  3. 3 mutation types that can contribute to the disease
  4. Wide range of clinical severity based upon?
  5. How can you tell A and B apart
A
  1. X linked
  2. A= blood clotting factor VIII; B=blood clotting factor IX
  3. Deletions, nonsense mutations, DNA inversions
  4. Clotting factors level of activity
  5. Clinically the same, need further testing to determine which one
21
Q
  1. Which is more common? In males or females?

2. Clinical presentation

A
  1. A - males

2. Prolonged bleeding episodes, intracranial hemorrhage, easy bruising, hemarthrosis

22
Q
  1. What is hemarthrosis
  2. Most frequent cause of death for hemophiliacs ?
  3. Treatment
A
  1. Bleeding into joints/loss of joint mobility
  2. AIDs
  3. Factor replacement therapy (via infusion)
23
Q

Duchenne and Becker Muscular dystrophy (DMD and BMD):

  1. Type of disease
  2. Gene defect in both
  3. Describe this gene
  4. Size of this gene, why it is significant
A
  1. X linked
  2. Dystrophin for both
  3. Protein involved in cytoskeleton of muscle and brain cells
  4. Huge - thought to be the reason why mutations occur more frequently compared to some other genes
24
Q
  1. DMD-what type of mutation
  2. BMD-what type of mutation? How does it present
  3. Which is more common?
A
  1. Insertions/deletions causing frameshifts (not a factor of 3)
  2. Insertions/deletions that are a factor of 3 - results in partially functional dystrophin protein and milder symptoms
  3. DMD
25
Q
  1. DMD - clinical presentation? When does it become apparent? Age of death?
  2. BMD - clinical presentation? When does it become apparent? Age of death?
  3. Treatment
A
  1. Progressive muscle wasting/cognitive impairment. Wheel chair bound. Age 5. Early 20s from respiratory/cardiac insufficiency
  2. Similar symptoms but less severe. Apparent at 11. Death ~42
  3. No curative treatment, therapeutic only
26
Q

Fragile X syndrome:

  1. Type of disease
  2. Cause?
  3. Clinical presentation
  4. Most common INHERITED cause of ?
  5. Most common known cause of?
A
  1. X linked
  2. Trinucleotide repeat expansion (FMR1), 5’ non-coding region
  3. Long face, large ears and mandible, macro-orchidism (large testes)
  4. Mental impairment
  5. Autism
27
Q
  1. Fragile X syndrome appears in some females due to ?
  2. How will an inactive X chromosome look under EM?
  3. Altered chromatin structure is associated with
  4. X inactivation is fixed and incomplete - what does that mean
A
  1. Lyonization (X inactivation) of a percentage of the normal X chromosome
  2. Highly condensed Barr body in the nuclei
  3. Highly methylated DNA
  4. Fixed= all cells that descend from the inactivated X will also have an inactivated X; incomplete= some genes remain available for transcription
28
Q

Color blindness is what type of disease?

A

X linked

29
Q

Name 2 single gene disorders that do not manifest until later in life

Onset?

A

Huntington disease and myotonic dystrophy

~30-40s

30
Q

Locus heterogeneity:

  1. Define
  2. Example of a disease
  3. Can display several different?
A
  1. When the same disease phenotype can be caused by mutations in different genes
  2. Ehlers-danlos syndrome (EDS)
  3. Inheritance patterns (autosomal dominant, recessive or X linked)
31
Q

Name the mutation in the following:

  1. EDS autosomal dominant
  2. EDS autosomal recessive
  3. EDS X linked
A
  1. Collagen genes
  2. Lysyl hydroxylase
  3. Copper binding protein (gene located on X chromosome)
32
Q

EDS X linked

  1. Mutation in copper binding protein leads to?
  2. What is copper essential for?
A
  1. Reduced copper availability in the serum

2. Activity of lysyl oxidase (cross linking of collagen fibers)

33
Q

30% of cases of DMD (X linked) result from? From which parent?

A

New mutations inherited from the mother

34
Q

Anticipation

  1. Define
  2. Most associated with diseases caused by?
  3. 3 examples of these type of diseases
  4. Severity of disease is directly correlated to?
A
  1. Most recent generation of affected individuals show an earlier onset and/or more severe symptoms than the previous generations
  2. Trinucleotide repeat expansions
  3. Fragile X, myotonic dystrophy, and Huntington
  4. Length of the segment containing repeats
35
Q

Hardy-Weinberg

  1. 2 assumptions?
  2. Relationship between?
  3. Allows us to determine?
A
  1. Population is large and individuals mate at random with respect to their genotypes at a given locus
  2. Genotype frequencies and gene frequencies
  3. Genotype frequencies if we know the gene frequencies and vice versa
36
Q
  1. What is the primary source of all new genetic variation in populations
  2. Do these rates differ much from population to population
A
  1. Mutations

2. No

37
Q
  1. Natural selection influences ___, how?
  2. What helps explain why most genetic diseases are relatively rare?
  3. Which has lower gene frequencies: diseases that require only a single copy of a mutant gene or diseases that can remain hidden in heterozygotes?
A
  1. Gene frequencies by selecting for genes that promote survival/fertility (fitness)
  2. Reduced fitness of disease genes
  3. Diseases that require a single copy of a mutant gene have lower gene frequencies
38
Q

Name a recessive gene (disease) that has a very high rate

A

Sickle cell anemia

39
Q
  1. Heterozygotes for thalassemia mutations have some protection against?
  2. Heterozygotes for cystic fibrosis mutation are protected against?
A
  1. Malaria

2. Typhoid fever

40
Q

Genetic drift

  1. Occurs in what kind of populations
  2. Another name?
  3. More cases of what disease are seen in old order amish?
A
  1. Populations with finite sizes (small)
  2. Founder effect
  3. Ellis van creveld disease
41
Q

Ellis van Creveld disease

  1. Type of disease
  2. Gene mutation
  3. Symptoms
A
  1. Very rare autosomal recessive
  2. EVC gene
  3. Polydactyly and short limbed dwarfism
42
Q

Gene flow:

  1. Results from
  2. Why is gene flow being seen more frequently ?
A
  1. Exchange of genes among populations

2. Many parts of the world are becoming less isolated - breeding between different populations

Biochemistry Block 4 (9 decks)

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