Respiratory Channelopathies

Question 1

What type of disease is cystic fibrosis?

Answer 1

Autosomal recessive

Question 2

What does cystic fibrosis broadly effect?

Answer 2

Epithelial tissues, especially in the lungs

Question 3

How many people are carriers for cystic fibrosis?

Answer 3

1 in 20

Question 4

What is the incidence of cystic fibrosis?

Answer 4

1 in 2,500 births

Question 5

What are the impacted organs of cystic fibrosis?

Answer 5

The liver - 5% blocked causes liver function problems
The pancreas - 65% of blockage in ducts prevents digestion
The small intestine - 10% of newborns have a SI blockage
Reproductive tract - 95% of males with CF have no vas deferens
Skin - excess NaCl via sweat makes skin salty to taste

Question 6

What are the clinical manifestations of CF from birth?

Answer 6

1 day to a month - meconium ileus (blockage of the SI)
1 week to 30 - pancreatic insufficiency
1 month - Distal intestinal obstruction syndrome and respiratory disorders manifest
1 - 2 years old - Liver disease manifests
3 years old - male infertility can be detected

Question 7

Where is the mutation in CF?

Answer 7

In the cystic fibrosis transmembrane conductance regulator

Question 8

How many transmembrane spanning domains does CFTR have?

Answer 8

12

Question 9

How is CFTR opening/closing regulated

Answer 9

On the regulatory domain by pka phosphorylation

Question 10

What are NBD1 and NBD2?

Answer 10

Sequences which ATP binds to

Also regulates opening and closing

Question 11

How many mutations are there that can cause cystic fibrosis?

Answer 11

Over 1900

Question 12

What is the most common mutation causing cystic fibrosis?

Answer 12

Changes in F508 (mutation in the NBD1 sequence

Question 13

What can mutations in CFTR impact on?

Answer 13

Conductance - pore does not allow ions through
Regulation - Protein does not open/close properly
Trafficking - Protein does not reach the membrane
Processing - Truncated proteins, misfolding
Production - no or not enough mRNA

Question 14

What is the allelic frequency of F508 mutation?

Answer 14

90%

Question 15

What other mutations are there in the CFTR gene which have around a 1-3% allelic frequency?

Answer 15

G55ID
WI282x
G542x
NI303k

Question 16

What is the pathology of the lungs in CF?

Answer 16

Viscous mucous in the airways
Recurrent bacterial infections
Inflammation - due to an immune response
Tissue degeneration

Question 17

Why do patients with CF show recurrent bacterial infections?

Answer 17

They develop antibiotic resistance so ability to treat infections succesfully decreases over time

Question 18

How do 70% of CF patients die?

Answer 18

Due to tissue degeneration so life is no longer sustainable

Patients have to breathe 100% oxygen near death

Question 19

Where is NKCC1 located and what does it do?

Answer 19

On the basolateral membrane of epithelial cells, driving force for sodium influx

Question 20

What is created when the CFTR channel opens?

Answer 20

Cl- moving out of the cell creates a driving force for sodium and water to move from the basolateral membrane to the apical membrane

Question 21

What is the pelicilary layer?

Answer 21

A liquid layer on top of epithelial cells
Mucus sits on top of this liquid layer
Needs to be at the optimum for cilia to work properly

Question 22

What is the optimum height for the pelicilary layer?

Answer 22

7 um

Question 23

What happens if CFTR is missing in the epithelial cell model?

Answer 23

Sodium reabsorption by ENaC increases so the water n the pelicilary layer is pulled back so its height falls below 7um

Question 24

What is ENaC usually supressed by?

Answer 24

CFTR

Question 25

What happens if the pelicilary layer decreases below 7um?

Answer 25

The cilia bend over so they can’t beat properly

The patient struggles to clear mucous

Question 26

What happens when the too much liquid is added to the pelicilary layer in:

a) WT
b) CFTR mutation

Answer 26

a) Overtimes the height of the layer falls back to normal 7um
b) The height continues to fall to about 2-3 um

Question 27

What does the F508 mutation do?

Answer 27

Affects trafficking to the membrane of CFTR
The protein is misfolded so it is instantly degraded
If the misfolding is corrected so the CFTR can reach the membrane the CFTR works nearly as effectively as the wild type

Question 28

Why is the cystic fibrosis mutation so common?

Answer 28

In the colon water content of faeces is determined by CFTR (Cl- secretion in the colonic crypt means water flows outwards
Cholera enterotoxins activate CFTR = diarrhoea = dehydration = death
A carrier of CF will have some protection from cholera as some water is reabsorbed, increasing the mutation frequency

Question 29

What are the current treatments for the symptoms of CF?

Answer 29

Physiotherapy
Bronchodilator drugs
Antibiotics
Steroids - decrease inflammation
Mucolytics - break down mucus eg Dnase

Question 30

Why is gene therapy for CF challenging?

Answer 30

Poor success rate - epithelial cells renew

Expensive to do

Question 31

What are CFTR modulators?

Answer 31

Used to treat the cause of CF

Read through agents, correctors, potentiators or can be used in combinations

Question 32

What is the impact of using a potentiator in vitro?

Answer 32

Very succesful against G55ID mutation - increases the height of fluid layer close to the optimum
Effective over a long term period
Reduces the likelihood of secondary problems
Sweat chloride concentrations drop below 60mmol (clinical threshold) from 100mmol