CBC- Cystic Fibrosis

Question 1

T or F. Mendelian disorders are caused by dysfunction of a single gene

Answer 1

T.

Question 2

What is the mode of inheritance of Cystic Fibrosis?

Answer 2

autosomal recessive

Question 3

CF primarily affects what ethnicity?

Answer 3

White. European descent.

although cystic fibrosis has been reported in all races and ethnicities

Question 4

What trans are affected by CF?

Answer 4

Abnormally viscous secretions in the airways of the lungs and in the ducts of the pancreas in individuals with cystic fibrosis cause obstructions that lead to inflammation, tissue damage and destruction of both organ systems . Other organ systems containing epithelia — such as the sweat gland, biliary duct of the liver, the male reproductive tract and the intestine — are also affected

Loss of pancreatic exocrine function results in malnutrition and poor growth, which leads to death in the first decade of life for most untreated individuals.

Question 5

What is the primary cause of death related to CF?

Answer 5

Obstructive lung disease is currently the primary cause of morbidity and is responsible for ~80% of mortality.

Question 6

What is the most common cause of CF?

Answer 6

a variant (p.Phe508del; also known as F508del in legacy nomenclature) in the cystic fibrosis transmembrane conductance regulator (CFTR) gene is the most common cause of cystic fibrosis

CFTR functions as a chloride channel regulated by cyclic AMP (cAMP)-dependent phosphorylation

Question 7

Notes on variant of CF

Answer 7

40% are predicted to cause substitution of a single amino acid, 36% are expected to alter RNA processing (including nonsense, frameshift and mis-splicing variants), ~3% involve large rearrangements of CFTR, and 1% affects promoter regions; 14% seem to be neutral variants, and the effect of the remaining 6% is unclear.

Question 8

What does F508del cause?

Answer 8

F508del causes aberrant folding of CFTR and subsequent degradation of the majority of the synthesized protein

The minor fraction of F508del-CFTR that is trafficked to the cell membrane has severely reduced membrane residency and aberrant chloride channel function1

Question 9

What are the major motifs of CFTR?

Answer 9

domains that inter- act with ATP, termed nucleotide-binding domain 1 (NBD1) and NBD2; regions that anchor the protein in the membrane known as membrane-spanning domain 1 (MSD1) and MSD2; and an area containing numerous sites for phosphorylation called the regulatory domain (also known as the R domain)

deletion of phenylalanine at codon 508 (F508) causes instability of NBD1

disease-causing missense variants outside the NBD1 domain — notably, a cluster in the fourth cytosolic loop (CL4) within MSD2 — also cause misfolding of the protein2

Question 10

Where does F508 occur?

Answer 10

F508 occurs at an interface between NBD1 and CL4, and seems to be capable of forming hydrogen bonds with arginine at codon 1070 (R1070)

Restoration of NBD1 assembly using suppressor mutations produces only par- tial recovery of CFTR processing, which indicates that the F508del variant also affects interactions elsewhere in the full-length protein

introduction of the disease-associated p.Arg1070Trp (legacy R1070W)29 variant in CL4 and correction of NBD1 misfolding using synthetic suppressor mutations could restore process- ing to F508del-CFTR

Question 11

Notes on stem cells for tissuing

Answer 11

Human embryonic stem cells and intestitonal stem cells from individuals with cystic fibrosis have been coaxed into differentiating into secretory epithelial cells that manifest defects in CFTR-mediated chloride transport

These methods provide new tissue models for examining function and dysfunction of CFTR from individuals with specific CFTR genotypes.

Question 12

How have animals been used to investigate CF?

Answer 12

The Cftr gene in mice has been extensively manipulated to derive lines that do not express CFTR and lines that express CFTR bearing variants equivalent to those observed in humans

Even though airway epithelial cells display ion trans- port abnormalities that are consistent with loss of CFTR function, overt lung disease is not evident in newborn or young mice with cystic fibrosis. The absence of lung disease similar to that seen in humans with cystic fibrosis has been ascribed to the presence of alternative path- ways for chloride transport in mouse epithelial cells. This observation suggests that ion channels other than CFTR might be exploited to recover chloride transport in cystic fibrosis cells

Question 13

What is one of the key issues in the early stages of human cystic fibrosis?

Answer 13

the genesis of inflammation in the lungs. Some studies suggest that infection of the airways trigger inflammation, whereas others demon- strate the presence of an inflammatory response in the absence of lung infection
This distinction is important, as treatment strategy of each scenario is markedly different

Question 14

What are some important drivers of early-stage lung disease in CF?

Answer 14

The cystic fibrosis pig model provides compelling evidence that loss of chloride and bicarbonate transport, maldevelopment of the airways and infection are the important drivers of early-stage lung disease in cystic fibrosis.

Question 15

What is the primary cause of intestinal obstruction in cystic fibrosis?

Answer 15

loss of CFTR function in the intestine rather than pancreatic exocrine dysfunction is the primary cause of intestinal obstruction in cystic fibrosis

Question 16

T of F. Diabetes affects many of those with CF

Answer 16

T.

Diabetes mellitus is an age-dependent complication that affects 40% of individ- uals with cystic fibrosis by 35 years of age; this disorder is also closely correlated with pancreatic exocrine dysfunction. Destruction of the exocrine pancreas has been proposed to stress the endocrine pancreas, which leads to loss of insulin-secreting observations suggest that cystic fibrosis- related diabetes is the result of an intrinsic defect in the endocrine pancreas caused by loss of CFTR function.

observations suggest that cystic fibrosis- related diabetes is the result of an intrinsic defect in the endocrine pancreas caused by loss of CFTR function.

Question 17

How much of the difference of lung function severity in individuals with CF is related just to genetics?

Answer 17

~50%

The remaining variation was due to environmental exposures, primarily those unique to each individual, and to stochastic factors. Together, these family-based studies demonstrate that genetic modifiers have considerable influence on lung function variation in cystic fibrosis.

Question 18

What other aspects of CF are genetically related?

Answer 18

Establishment of chronic P. aeruginosa infection and age at establish- ment are highly influenced by genetic factors

Affected-twin analysis also revealed that genetic modifiers are primarily respon- sible for the age at onset of diabetes

obstruction of the small intestine

Question 19

TGFB1 as a modifier primarily in individuals who are what?

Answer 19

homozygous for the common cystic fibrosis-causing variant F508del

Question 20

What does ivacaftor do?

Answer 20

increased chloride transport of primary airway cells bearing the G551D variant up to ~50% of wild-type level and reduced sweat chloride concentra- tion (to an average concentration below the diagnostic threshold of 60 mM) in individuals with cystic fibrosis carrying the G551D variant

Question 21

What does lumacaftor do?

Answer 21

A clinical trial of lumacaftor produced a dose-dependent improvement in CFTR function measured in the sweat gland of patients carrying the F508del variant

However, CFTR function was not augmented in nasal epithelia, and lung function measures were not improved

A Phase II clinical trial demonstrated that the combination of lumacaftor and ivacaftor improved measures of lung function and sweat chloride concentration in individuals homozygous for the F508del variant

Question 22

What causes crackles (abnormal lung sounds)

Answer 22

fluid buildup in the lungs

Question 23

What is the main source of bacterial infection of the lungs in CF?

Answer 23

Psuedomonas (gram-negative)- forms a biofilm around itself that makes antibiotics harder to enter

Question 24

Treatment of CF

Answer 24

Hypertonic saline (7%) to promote cough- actively pulls water into the airway for enhancing coughing/secretion

Question 25

How does azithromycin work?

Answer 25

Disrupts the biofilm laid down by bacteria during infection

Question 26

Proteins with G551D do what?

Answer 26

Are fully properly and delivered to the epithelium but does not have chloride channel functionality