CF - L1

Question 1

What are the respiratory clinical features and what are they due to?

Answer 1

Frequent coughing
Chronic infections
Lung
damage

Due to:
obstruction of bronchioles by mucus
colonisation by bacteria, especially antibiotic resistant
strains
damage (fibrosis) caused by inflammatory responses

Question 2

What are the digestive clinical features and what are they due to?

Answer 2

Failure to thrive
chronic malnutrition

Due to:
blockage of various intestinal and pancreatic ducts by mucus
poor digestion of fats (mainly) and proteins
Intestinal obstruction in newborns (‘meconium ileus’;
15% of neonates with CF)
‘Pancreatic insufficiency’ (85% of patients)
Chronic pancreatitis (& diabetes, 40% of adults), liver disease (≥5%)

Question 3

What are the reproductive clinical features and what are they due to?

Answer 3

Infertility in males
Sub-fertility in females

Due to:
blockage of vas deferens in males, leading to fibrosis or usually atrophy: congenital bilateral absence of the vas deferens (CBAVD)
cervical mucus in females acting as barrier to passage of sperm
females may be anovulatory

Question 4

When was the CFTR discovered?

Answer 4

1989, by positional cloning of 7q31.2

Question 5

How many exons does CFTR have?

Answer 5

27, used to think 24 (6,14,17)

Question 6

Where is CFTR expressed?

Answer 6

epithelial cells on the apical side

Question 7

What family is CFTR from and how is it regulated?

Answer 7

member of ABC family of membrane transporters and is regulated by cAMP-dependent phosphorylation

Question 8

What are the domains of CFTR?

Answer 8

MSD1&2, NBD1&2, RD

Question 9

Describe the molecular mechanism of CFTR

Answer 9

phosphorylation of the regulatory domain: by PKA
allows ATP to bind to the NBDs
the NBDs undergo a conformational change
this causes the MSDs to open and allow ions to flow
hydrolyses: one ATP transforms to ADP and Pi
ADP and Pi are released leaving just one ATP molecule bound and the channel closed

Question 10

What are the other functions of CFTR beside chloride transport?

Answer 10

Influences proteins responsible for:
conductance
regulation of other channels (ENaC)
signal transduction

Question 11

What happens in the lung on a molecular level in CF?

Answer 11

Cl can’t go down conc gradient, lots of Na and H2O move into the cell, leaving the outside dehydrated

Question 12

What happens in the sweat duct on a molecular level in CF?

Answer 12

Cl cannot enter the cell, Na and water remain in the sweat duct, making it salty

Question 13

What is the Class I mutation?

Answer 13

no protein production (nonsense, frameshift)

Question 14

What is the Class II mutation?

Answer 14

defective processing

Question 15

What is the Class III mutation?

Answer 15

defective regulation

Question 16

What is the Class IV mutation?

Answer 16

defective/reduced ion conductance or channel gating

Question 17

What is the Class V mutation?

Answer 17

reduced protein production

Question 18

What is the Class VI mutation?

Answer 18

accelerated turnover from cell surface

Question 19

What class is F508del and what happens?

Answer 19

Class II

causes protein to misfold, mutant protein is retained in the ER then degraded

Question 20

Why is F508del not actually in frame?

Answer 20

The redundancy of the genetic code means ATC and ATT both code for isoleucine

Question 21

What are RFLPs?

Answer 21

restriction fragment length polymorphisms used for mutation testing

Question 22

Name 3 types of common mutation testing?

Answer 22

mutation panel
SNP analysis
SNP genotyping by MALDI-TOF MS