Cystic Fibrosis

Question 1

Inheritance of CF?

Answer 1

Autosomal recessive

Question 2

Gene involved in CF?

Answer 2

Cystic fibrosis transmembrane conductance regulator (CFTR) gene

Question 3

What is the most freq. life-shortening genetic disease in US?

Answer 3

Cystic fibrosis

Question 4

What is CFTR?

Answer 4

–Chloride and bicarbonate ion channel found on apical surfaces of epithelial cells

Question 5

Structure of CFTR?

Answer 5

• -12 membrane spanning domains that form pore for Cl- ion channel
• -Nucleotide binding domains and R domain provide regulatory sites that promote channel opening

Question 6

What is the primary cause of death in CF?

Answer 6

Respiratory failure in 90% of cases

Question 7

Ave. survival w/CF?

Answer 7

37.4 yrs

Question 8

Clinical consequences of CF?

Answer 8

• -Respiratory failure
• -Liver disease
• -Pancreatic insufficiency
• -CF diabetes
• -Intestinal obstruction, malabsorption, CA
• -Male infertility

Question 9

Function of normal CFTR?

Answer 9

• -When open HCO3- and Cl- flow in direction of EC gradient (out of cell)
• -Controls luminal ion concentrations and PH
• -Controls movement of H2O to apical surface of airway epithelial cell

Question 10

What direction can CL- ions and H2O flow through CFTR channel?

Answer 10

Can only flow out if open

Question 11

What is required for opening of channel?

Answer 11

1. PKA phosphorylates R domain
2. Two ATP bind NBD domains

PKA activated in response to cAMP

Question 12

Apical export of Cl- by CFTR

Answer 12

1.CFTR is a chloride ion channel located on the apical surface of epithelial cells.
2.Export of Cl- into the lumen creates an osmotic gradient for the movement of water to the lumen mainly through a paracellular route.
3.CFTR is a channel so Cl- moves down the electrochemical gradient.
Basolateral channels and transporters create electrochemical conditions that favor export of Cl-.
Paracellular movement of Na+ prevents build up of negative charge that would create an unfavorable gradient.
4.ENaC counter acts and balances CFTR, pulls H20 in

Question 13

Where is the CFTR gene found? How long is it?

Answer 13

Long arm of chromosome 7

250,000 bp

Question 14

What ethnic group has the highest incidence of CF? The lowest?

Answer 14

Caucasian: highest

Asian-American: lowest

Question 15

How many mutations have been identified?

Answer 15

> 1900

Only 5 mutations in 95% of cases

Question 16

What does it mean for Tx with different CFTR mutations and incidence?

Answer 16

• -Mutation based diagnostic tests feasible if tailored to ethnic group
• -Molecular based therapies are feasible

Question 17

Mutation class 1

Answer 17

• No protein produced. -Nonsense mutation creates stop codon. -Often mRNA degraded.
• G542X, 5% of CF alleles

Question 18

Mutation class 2

Answer 18

• Defective protein folding
• Activates ER quality control
• Degradation of protein
• F508del, 70% of CF alleles

Question 19

Mutation class 3

Answer 19

• Defective gating or regulation of channel opening

- G551D, 4% of CF alleles

Question 20

Mutation class 5

Answer 20

Normal CFTR produced, but decreased amounts

Question 21

Mutation class 4

Answer 21

Defective in ion transport

Question 22

Severe CFTR mutations

Answer 22

-Class 1, 2, 3

-

Question 23

Less severe CFTR mutations

Answer 23

• Class 4, 5
• About 5% of CFTR activity remaining
• May have late presentation
• Survival to 50 not uncommon
• Pancreatic sufficient

Question 24

5 CFTR mutations

Answer 24

1. F508del
2. G542X
3. G551D
4. W1282X
5. N1303K

All in severe category

Question 25

F508del

Answer 25

- -Most common CFTR mutation - -Almost complete loss of functional proteins - -Folding defect leads to degradation of most - -Small fraction of protein at cell surface defective in gating and stability

Question 26

Synthesis of CFTR protein

Answer 26

- -In ER - -Needs inta-domain folding and inter-domain interactions - -Needs interaction w/series of chaperones

Question 27

What does the F508del result in?

Answer 27

- -Incorrect folding of NBD1 domain where it is location and incorrect interaction of NBD1 w/other domains. - -Altered interaction with chaperones - -Retention in ER and activation quality control pathways - -Degradation by proteosome

Question 28

Does mutation class predict the severity of disease in individuals?

Answer 28

No. Those classified as severe are there because they cause defects in pancreatic ducts, tend to have worse pulmonary disease. Other factors influence outcome

Question 29

Are severe mutations sufficient for development of CF-related diabetes and liver disease?

Answer 29

No. The mutations are necessary, but not sufficient.

Question 30

Why does inactivation of CFTR affect respiratory function?

Answer 30

- Loss of luminal H2O and ion balance - -HCO3- required for expansion of mucin after secretion, if absent, cilia can't move properly and clear bacteria - -Inflammation

Question 31

How does inflammation affect respiratory function?

Answer 31

1. Decreased ASL, ineffective mucin barrier failure to clear bacteria 2. Inflammatory pathways activated (LPS > TLR4 > MyD88 > NFkB) 3. Increased mucin secretion (ineffective) 4. Inflammatory mediators (TNF-a, IL-8) recruit neutrophils 5. Neutrophils release elastase, damage CFTR and epithelial cell DAMPs further stimulate inflammatory signaling.

Question 32

Path of respiratory failure

Answer 32

1. Decreased ASL layer --> builds up viscous mucus --> fail to clear bacteria 2. Persistent colonization and desicated mucus --> inflammation 3. Infection, inflammation and mucus plugging --> long-term structural damage 4. respiratory failure

Question 33

What is the primary thing that must be known when considering what causes chronic airway infection and permanent damage?

Answer 33

Decreased ASL layer

Question 34

What is the cause of death for most ind. w/ CHF?

Answer 34

Pulmonary failure

Question 35

Major organisms involved in infection

Answer 35

``` H. influenzae Staph aureus Pseudomonas aeruginosa MRSA Burkholderia cepacia ```

Question 36

Tx mainstays to try and prevent pulmonary damage

Answer 36

1. Chest physiotherapy to improve drainage 2. Aggressive rx of infection w/antibiotics 3. Hypertonic saline and DNase aerosols to make mucus less viscous 4. Anti-inflammatories