Cystic fibrosis

Question 1

what is cystic fibrosis

Answer 1

• an autosomal recessive disorder caused by mutations in CFTR gene.
• most common mutation causes delta F508 , a codon deletion

Question 2

symptoms of CF

Answer 2

• malabsorption
• salty skin
• meconium ileus
• chronic obstructive lung disease w/ bronchiectasis
• excess mucous production ( leading to respiratory infections)
• pulmonary exacerbations

Question 3

ways to test for CF

Answer 3

• sweat test ( chloride ions )
• genetic testing
• CFTR physiologic testing

Question 4

microorganisms responsible for CF

Answer 4

• staphylococcus aureus is the most common cause of recurrent pulmonary infection in infancy and childhood
• Pseudomonas aeruginosa is the most common cause of recurrent pulmonary infections in adulthood

Question 5

Newborn screening

Answer 5

• ## heel prick blood sampling in the first 24 hours of life

Question 6

The role of immunoreactive trypsinogen (IRT)

Answer 6

• immunofluorescence assay measures levels of IRT
• ## elevated IRT levels: CF possible

Question 7

CF screening methods

Answer 7

• combine CF screening methods to minimize false-positive and false-negative newborn screening (NBS) results
• patients who test positive for CF during newborn screening should undergo a sweat test, ideally in the first 4 weeks of life.
• the presence of : positive NBS, first-degree family member with CF
• sweat chloride value of above 60 mmol/L
• patients with suspected CF undergo a sweat test and CFTR genetic testing to help identify mutations that may affect management

Question 8

Why is sweat salty in CF

Answer 8

Intracellular Cl- is transported across the cell membrane into the lumen through the CFTR Cl channel.
in sweat glands, cL goes the opposite direction from the lumen into the cell
in CF a defect in CFTR Cl - channel results in an accumulation of CL- and Na in the lumen of sweat glands –> increase in conc of NaCL in sweat

Question 9

CF and hypokalemia

Answer 9

sweat losses of NaCl and water leads to contraction of ECF volume and RAAS activation. This leads to increased renal absorption of NaCl and water, and excretion of H+ and K+ causing alkalosis and hypokalemia