Cystic fibrosis

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Cystic fibrosis

Respiratory system


Cystic fibrosis


0 / 19 complete

USMLE® Step 1 questions

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High Yield Notes

13 pages


Cystic fibrosis

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USMLE® Step 1 style questions USMLE

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A 14-year-old boy is brought to the clinic by his parent for a routine checkup. The patient has cystic fibrosis and has had multiple hospitalizations in the past for pulmonary infections. The patient is currently on albuterol, inhaled N-acetylcysteine, oral ibuprofen, and a combination of lumacaftor and ivacaftor. The patient states he feels fine today. Vital signs are within normal limits. Weight is at the 10th percentile for age and height is at the 10th. Digital clubbing is present. The patient’s parent recently read about the medication dornase alfa that is supposedly effective in treating cystic fibrosis. The mechanism of action of which of the following medications is most similar to dornase alfa?  

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cystic fibrosis p. 58


in cystic fibrosis p. 58

Biliary cirrhosis p. 398, 402

cystic fibrosis p. 58


cystic fibrosis p. 58


cystic fibrosis p. 58

Burkholderia cepacia

cystic fibrosis p. 176

Chloride channels

cystic fibrosis p. 58

Cirrhosis p. 398

cystic fibrosis p. 58

Clubbing (nails)

cystic fibrosis p. 58

Cystic fibrosis p. 58

Aspergillus fumigatus p. , 150

bronchiectasis p. 700

chromosome association p. 62

common organisms p. 176

meconium ileus in p. 395

N -acetylcysteine p. 711

pancreatic insufficiency p. 390

vitamin deficiencies and p. 63

Hypokalemia p. 615

cystic fibrosis p. 58


cystic fibrosis p. 58

Liver disease

cystic fibrosis p. 58

Meconium ileus p. 395

cystic fibrosis p. 58

N -acetylcysteine p. 711

for cystic fibrosis p. 58

Nasal polyps

cystic fibrosis p. 58

Pediatric patients

cystic fibrosis p. 58

Pseudomonas spp.

cystic fibrosis p. 58, 176

Sodium channels

cystic fibrosis p. 58

Staphylococcus aureus p. , 133

cystic fibrosis p. 58, 176


cystic fibrosis p. 58

Streptococcus pneumoniae p. , 134

cystic fibrosis p. 176


You’re probably aware that cystic fibrosis, or CF, is a genetic disorder that affects the lungs, but that’s only part of the story.

In fact, the name “cystic fibrosis,” refers to the disease’s effects on the pancreas, where it can lead to cysts, which are fluid-filled sacs wrapped in a membrane and fibrosis—excess deposition of connective tissue that can replace or infiltrate normal tissue in an organ.

CF is an autosomal recessive disorder involving the CFTR gene, which stands for “cystic fibrosis transmembrane conductance regulator,” and this gene codes for the CFTR protein.

CF develops when there’s a mutation in the CFTR gene, but because it’s autosomal recessive, you need to inherit two mutated CFTR genes, one from mom and one from dad.

Now if mom and dad both have one copy of the mutated gene and one normal gene, they’re considered carriers and don’t have the disease.

Inheriting CF is more common in people of European descent.

The CFTR protein is a channel protein that pumps chloride ions into various secretions, those chloride ions help draw water into the secretions, which ends up thinning them out.

The most common mutation is the “∆F508” mutation.

Delta means a deletion, and the F (which can also be written as “Phe”) is short for phenylalanine, and the 508 is the five hundred and 8th amino acid in the CFTR protein.

So, the ∆F508 mutation is where the 508th amino acid out of 1480, phenylalanine, is deleted and missing.

This CFTR protein with the ∆F508 mutation gets misfolded and can’t migrate from the endoplasmic reticulum to the cell membrane, meaning there’s a lack of CFTR protein on the epithelial surface, and this means that it can’t pump chloride ions out, which means water doesn’t get drawn in, and the secretions are left overly thick.

In a newborn, thick secretions can affect the baby’s meconium, or first stool, or, which can get so thick and sticky that it might get stuck in the baby’s intestines and not come out, and this is called a meconium ileus and is a surgical emergency.

In early childhood, pancreatic insufficiency is the most prominent effect of CF.


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  3. "Pathophysiology of Disease: An Introduction to Clinical Medicine 8E" McGraw-Hill Education / Medical (2018)
  4. "CURRENT Medical Diagnosis and Treatment 2020" McGraw-Hill Education / Medical (2019)
  5. "Cystic Fibrosis: Lessons from the Sweat Gland" Physiology (2007)
  6. "Infection Control in Cystic Fibrosis" Clinical Microbiology Reviews (2004)
  7. "Pharmacological approaches for targeting cystic fibrosis nonsense mutations" European Journal of Medicinal Chemistry (2020)

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