Cystic Fibrosis: Molecular Basis and Genetics

Question 1

Recall a brief overview on CF

Answer 1

Question 2

Mention the organ systems affected by CF and how is affected.

Answer 2

Question 3

Recall the respiratory clinical features of CF.

Answer 3

Question 4

Recall the gastrointestinal clinical features of CF.

Answer 4

Question 5

Recall the reproductive clinical features of CF.

Answer 5

Question 6

Describe the CFTR gene.

Answer 6

Question 7

Describe the characteristic and function of CFTR protein.

Answer 7

Question 8

Recall the five domains of CFTR protein.

Answer 8

Question 9

Recall the following schematic diagram of CFTR showing its domain organisation.

Answer 9

Question 10

Activation of CFTR channel relies on ___________________.

Answer 10

Question 11

Recall the CFTR molecular mechanism.

Answer 11

MSD1 and MSD2 are represented by the dark and light blue rectangle respectively. NBD1 and NBD2 are represented by the dark and light green shape respectively, while the purple oval represents the R region.

Phosphorylation of the R region by PKA disrupts the interaction between NBD1 and R region, allowing ATP to bind at the NBDs. ATP binding induces the dimerisation of the NBDs, which causes a conformational change in the MSD region into an open conformation. The channel opens and Cl- flux occurs across the membrane.

Hydrolisation of ATP at one of the NBDs causes destabilization of the NBD dimer. Release of Pi and ADP rests the protein into a closed conformation and closes the channel gate.

Note: ATP may remain bound to one of the NBD, allowing for rapid transition back to open-ready state (after addition of another ATP). Alternatively, ATP is released and CFTR is restored to closed state.

Question 12

Recall how CFTR protein interacts with other protein.

Answer 12

Question 13

Recall CFTR function in airways and the effects of CF.

Answer 13

Question 14

Recall the following diagram showing effects of CFTR dysfunction.

Answer 14

Question 15

Majority of CFTR gene variants/mutations are found in _______________________.

Answer 15

Question 16

Recall the classes of CFTR mutations/variants.

Answer 16

Question 17

Recall the following table further elaborating the classes of CFTR mutations.

Answer 17

Question 18

Recall examples of CFTR variants/mutations.

Answer 18

Question 19

Describe the variant/mutation F508del in CF.

Answer 19

F508del accounts for ~ 70-75% of variants in people from northern European ancestry

Homozygosity for F508del in ~50% of patients with CF

Question 20

Recall mutation/variant class-specific therapies for CF.

Answer 20

Question 21

Recall a test for F508del in CF.

Answer 21

Testing typically used PCR ± restriction enzymes (RFLPs – restriction fragment length polymorphisms)

Question 22

Recall testing of variants by SNP analysis

Answer 22

• Multiplex PCR
  
  • single reaction, multiple primers, fluorescent tags
• Assay involves primer extension (mini-sequencing) of each hybridised primer so that each product incorporates a coloured fluorescent tag (dNTP) and the colour of the peak depends on which dNTP has been added (ie determined by the SNP):
  
  • A= green, C = blue, T = red, G= black
• Analysis of each variant (ie single nucleotide polymorphism, SNP) performed in 2 batches (multiplex A and B) on capillary gel electrophoresis

Question 23

Recall the process of SNP genotyping by MALDI-TOF MS

Answer 23

Matrix-Assisted Laser Desorption/Ionization–Time of Flight Mass Spectrometry

Can genotype large number of samples (several hundreds to thousands) and a medium number of SNPs (tens to hundreds)

Question 24

Recall the genetics of CF.

Answer 24

Question 25

Recall the worldwide prevalence of CF.

Answer 25

Question 26

Recall the typical pedigree of CF.

Answer 26

An obligate carrier is an individual who may be clinically unaffected but who must carry a gene mutation based on analysis of the family history; usually applies to disorders inherited in an autosomal recessive and X-linked recessive manner.

Question 27

Recall the correlation between genotype and phenotype of CF.

Answer 27

Question 28

Recall the clinical penetrance of R117H variant of CF.

Answer 28

Question 29

\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_, \_\_\_\_\_\_\_\_\_\_\_\_\_\_, _____________________ not well correlated with CFTR variants although under strong genetic influence

Answer 29

Question 30

Recall the ratio between genetic and environmental modifiers on various aspects of CF.

Answer 30

Question 31

Recall studies with twins and siblings in regards to CF.

Answer 31

Question 32

How to identify genetic modifiers of CF?

Answer 32

Question 33

Recall the use and limitations of GWAS in finding DNA sequence variants (SNPs) that could act as genetic modifiers for CF.

Answer 33

Question 34

Recall some genetic modifiers of different features of CF.

Answer 34

Question 35

Recall genetic modifiers of lung disease in CF.

Answer 35

Question 36

Recall genetic modifiers of other features in CF.

Answer 36

Question 37

Poorer health outcomes of CF associated with:

Answer 37

Question 38

Recall the different purposes of CF testing.

Answer 38

Question 39

Recall newborn screening for CF.

Answer 39

Question 40

Recall the CF newborn screening protocol.

Answer 40

Question 41

Recall reproductive options for CF carrier couples.

Answer 41

Question 42

Recall CFTR function in the lumen of duct sweat.

Answer 42