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BIOL 113 > Lecture 7 Single Gene Disorders > Flashcards

Lecture 7 Single Gene Disorders Flashcards

1
Q

What are single gene disorders caused by ?

A

Caused by point mutations in single genes

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2
Q

Autosomal recessive pedigree

A
  1. Males & females affected
  2. Disease absent from most generations
  3. Consanguinity (sexual relationship with blood relative) increases frequency of affected individuals
  4. Carriers have 25% chance of having affected child
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3
Q

Give 2 examples of autosomal recessive disorders

A

Cystic Fibrosis (CF)
Sickle cell anaemia (SCA)

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4
Q

What is the frequency of carrying cystic fibrosis recessive allele/what is carrier frequency for cystic fibrosis?

A

1 in ~25

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5
Q

What is frequency of CF births?

A

1 in ~2500
(1/25 x 1/25 x 1/4)

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6
Q

If untreated what happens to sufferers of cystic fibrosis ?

A

Sufferers die before their 5th birthday but now life can be extended into adulthood

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7
Q

What is Cystic fibrosis ?

A

Disorder originating in secretory epithelial tissue

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8
Q

Symptoms of CF

A
  • Accumulation of mucus in lungs,pancreas, digestive tract and other organs
  • Multiple effects including:
    Chronic bronchitis
    Recurrent bacterial infections
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9
Q

What is the CF gene called and what does it code for?

A

CF gene is CFTR = cystic fibrosis transmembrane conductance regulator

Codes for a chloride channel and regulates the flow of Cl- across the membrane

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10
Q

What is the most common mutation causing CF?

A

Delta/triangleF508

  • deletion of 3 base pairs results in the loss of a Phe residue at position 508
  • protein does not fold normally and is more quickly degraded
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11
Q

How many different CFTR mutations can cause CF?

A

> 800

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12
Q

How does the defect in CFTR cause CF?

A

Defect in Cl- transport causes extracellular mucus to become thicker and stickier

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13
Q

Treatment of CF

A

Life is prolonged by antibiotics and daily massage to clear away mucus

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14
Q

How many Afro-Caribbean or Afro-American births are affected by sickle cell anemia (SCA)?

A

Affects 1in 625 Afro-Caribbean or Afro-American births

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15
Q

Main symptoms of SCA (4)

A

Anaemia
Joint pain
Swollen spleen
Frequent severe infections

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16
Q

Treatment of SCA

A

Regular blood transfusions

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17
Q

Cure of SCA

A

Bone marrow transplant

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18
Q

What mutation cause SCA ?

A

A single nucleotide substitution in beta chain of haemoglobin has large negative effect

Instead of gluatamic acid, valine is coded for

Leads to incorrect folding of the protein

The defective haemogloblin forms long chains of rigid polymers (after O2 released) which deform red blood cells

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19
Q

What is sickle cell trait ?

A

Heterozygotes (carriers) also have phenotype in low oxygen conditions

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20
Q

What maintains the sickle cell allele in the population?

A

Selection for malaria resistance in carriers

21
Q

Autosomal dominant pedigree (3)

A
  1. Males and females affected
  2. Affected individuals have an affected parent
  3. 50% chance of affected parent having affected child
22
Q

Give 2 examples of autosomal dominant disorders

A
  1. Huntington’s Disease
  2. Familial Hypercholestrolaemia (FH)
23
Q

What is the occurrence of Huntington’s disease?

A

1 in 24,000

24
Q

Main symptoms of Huntington’s disease (4)

A
  1. Jerky movements
  2. Personality changes
  3. Deterioration of walking, speaking, and swallowing abilities
  4. Death will result from complications such as choking, infection or heart failure
25
What is Huntington’s disease?
Late-onset degeneration of the brain
26
HD is a late-onset disease how does this affect sufferers
So (before genetic testing) HD sufferers would usually have had children before they knew they had the disease
27
What is molecular cause of Huntington’s?
- Defect on chromosome 4 - Narrowed down to abnormalities in HD gene - HD gene contains CAG repeats (encoding glutamine) 11-34 repeats =normal 36-125 repeats = Huntington’s disease
28
Symptoms of Familial Hypercholesterolaemia (3)
1. High levels of cholesterol in the blood from an early age 2. Cholesterol deposits build up in joints 3. Cardiovascular disease
29
Treatment of FH (2)
1. Cholesterol lowering drugs e.g. statins 2. Low cholesterol diet
30
What is FH caused by ?
- Lack of low density lipoprotein (LDL) receptor - without LDL receptor the cholesterol accumulates in the blood
31
What does Low density lipoprotein do?
LDL binds to and carries cholesterol in the bloodstream
32
What is FH an example of ?
Incomplete dominance
33
Why is FH and example of incomplete dominance?
Because : - Homozygotes (hh) have a 6-fold increase in blood cholesterol - have heart attacks at age of 2 - Heterozygotes (Hh) have a 2-fold increase in blood cholesterol- heart attacks by age 35
34
What is the frequency of homozygote FH (hh) and heterozygote FH (Hh)?
hh - 1 in 1 million births Hh - 1 in 500 births
35
What is Fh dominant phenotype caused by ?
Haploinsufficiency
36
What are sex-linked conditions caused by ?
A gene on the X chromosome
37
Pedigree of sex-linked recessive trait ? (3)
- females are carriers, mostly males affected - carrier female will transmit to 50% of sons (affected) and to 50% of daughters (carriers) - affected male cannot transmit to sons but will transmit to 100% of daughters (carriers)
38
Give 2 examples of sex-linked recessive disorders?
1. Haemophilia 2. Duchenne Muscular Dystrophy
39
What is haemophilia ?
Blood clotting disorder
40
Symptoms of haemophilia (3)
1. Uncontrolled bleeding 2. Tendency to extensive bruising 3. Bleeding in joints
41
What mutation causes haemophilia A ?
Mutation in the gene for factor VIII (on X chrom.)
42
Incidence of haemophilia A?
1 in 5,000 males
43
What mutation causes haemophilia B?
Also known as Christmas disease Mutation in the gene for Factor IX (on X chrom.)
44
What is incidence of haemophilia B?
1 in 30,000 males
45
What is Duchenne Muscular dystrophy?
- A muscle wasting disease - the most frequent lethal childhood genetic disease (1 in 3500 males) - dystrophin gene disrupted in DMD
46
What does affected gene code for in Duchenne muscular dystrophy?
Affected gene codes for a muscle protein called dystrophin
47
Why is dystrophin gene prone to rearrangements?
It is very large - 2.6 million base pairs - largest known human gene
48
What is dystrophin/what does it do?
Is part of a protein complex that connects cytoskeleton of a muscle fibre to the surrounding extracellular matrix through the cell membrane
49
How do affected males die of DMD?
Muscles in DMD affected males progressively die Death occurs by age 20 from respiratory or cardiac failure

BIOL 113 (7 decks)

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