Cystic Fibrosis

Question 1

Inheritance pattern of CF

Answer 1

Autosomal recessive

Question 2

Affected gene and protein

Answer 2

Affected CFTR gene > CFTR protein

Question 3

Normal location and function of affected protein

Answer 3

Normally a chloride channel on epithelial cell membranes
- sinuses
- liver
- pancreas

Question 4

How most common variant alters folding of protein

Answer 4

F508 deletion mutation = CFTR protein is misfolded and cannot reach cell surface

F = phenylalanine

Question 5

WIP Principle of 3 different tiers of lab testing

Answer 5

1. Sweat Chloride Testing:
- positive in Newborn Screening
- family history
2. CFTR Genetic Analysis:
- genotyped for treatment
3. CFTR Physiologic Testing:
-

Question 6

Differentiate classes of CF

Answer 6

• based on quantity of protein
  Class I: no functional CFTR protein

Class II: trafficking defect; misfolded CFTR protein cannot reach cell surface

Class III: defective channel regulation; CFTR protein reaches cell surface but channels cannot open

Class IV: decreased channel conductance; CFTR protein reaches cell but channel function is decreased

Class V: reduced CFTR synthesis; not enough functioning CFTR protein on cell surface

Class VI: decreased CFTR stability; CFTR protein created but does not work at the cell membrane

Question 7

WIP Describe CRMS/ CFSPID

Answer 7

CF transmembrane conductance regulator-related metabolic syndrome OR CF screen positive inconclusive diagnosis

1. Positive IRT and negative sweat Cl test, has 2 CFTR mutations, one of which is unknown significance

OR

2.

Question 8

Treatment

Answer 8

1. Potentiators
   - increases CFTR channel transport of Cl
   - for Class III variant
2. Correctors
   - facilitates processing and trafficking of CFTR = increase CFTR on cell surface
   - increases stability of misfolded protein
   - for Class II variant (F508del)
3. Potentiator/ Corrector Combo
   - does both

Question 9

WIP Describe NBS of CF

Answer 9

Newborn screening:
- Immunoreactive trypsinogen; immunoassay detects high levels of trypsinogen in CF

Question 10

Why is trypsinogen detected in NBS for CF ?

Answer 10

Trypsinogen levels are increased in CF:
- trypsinogen produced by pancreas
- trypsinogen cleaved to trypsin in intestinal mucosa
- trypsin digests proteins > amino acids

Question 11

Describe the Sweat Chloride Test

Answer 11

• CFTR normally moves water (and NaCl) from pores back to the cell (sweat pore becomes hypertonic)
• iontophoresis of pilocarpine to stimulate sweat production by sweat gland
• sweat is collected in a capillary tube with blue dye
• [Cl-] is measured by coulometry

Question 12

Predictive testing

Answer 12

Suggests severity of disease

Question 13

Predictive testing

Answer 13

Suggests severity of disease

Question 14

Prognostic testing

Answer 14

Determines which therapies are beneficial

Question 15

Describe CFTR genotyping

Answer 15

Luminescent genetic assay:
- combine PCR and flow cytometry
- beads with different [dye/color] used to identify specific genotypes
- capture oligos attached to beads = bind specifically to (5’) primers of allele specific PCR
- exonuclease 1 degrades unused primers; SAP destroys unused dNTPs
- strepatvidin binds to biotinylated nucleotide; phycoerythrin is the fluorescent reporter

SAP = Shrimp alkaline phosphatase

Question 16

Describe CFTR physiologic testing

Answer 16

CR