Cystic fibrosis

Question 1

What is cystic fibrosis?

Answer 1

Cystic fibrosis (CF) is an autosomal recessive disorder causing increased viscosity of secretions (e.g. lungs and pancreas).

Question 2

What causes cystic fibrosis?

Answer 2

It is due to a defect in the cystic fibrosis transmembrane conductance regulator gene (CFTR), which codes a cAMP-regulated chloride channel.

Question 3

What is the prevalence of cystic fibrosis in the UK?

Answer 3

In the UK, 80% of CF cases are due to delta F508 on the long arm of chromosome 7. Cystic fibrosis affects 1 per 2500 births, and the carrier rate is approximately 1 in 25.

Question 4

Which organisms may colonise CF patients?

Answer 4

Organisms that may colonise CF patients include Staphylococcus aureus, Pseudomonas aeruginosa, Burkholderia cepacia, and Aspergillus.

Burkholderia cepacia was previously known as Pseudomonas cepacia.

Question 5

What is the sweat test result indicating cystic fibrosis (CF)?

Answer 5

A sweat chloride level greater than 60 mEq/l indicates CF. Normal value is less than 40 mEq/l.

Question 6

What are some causes of false positive sweat tests?

Answer 6

Causes include malnutrition, adrenal insufficiency, glycogen storage diseases, nephrogenic diabetes insipidus, hypothyroidism, hypoparathyroidism, G6PD, and ectodermal dysplasia.

Question 7

What is the most common reason for false negative sweat tests?

Answer 7

The most common reason is skin oedema, often due to hypoalbuminaemia/hypoproteinaemia secondary to pancreatic exocrine insufficiency.

Question 8

What are the presenting features of cystic fibrosis in the neonatal period?

Answer 8

Meconium ileus and less commonly prolonged jaundice.

Present in around 20% of cases.

Question 9

What percentage of cystic fibrosis patients experience recurrent chest infections?

Answer 9

40% of patients experience recurrent chest infections.

Question 10

What are the signs of malabsorption in cystic fibrosis?

Answer 10

Steatorrhoea and failure to thrive.

Seen in about 30% of patients.

Question 11

What are some other features of cystic fibrosis?

Answer 11

Liver disease.

Present in about 10% of patients.

Question 12

What percentage of cystic fibrosis patients are diagnosed after the age of 18 years?

Answer 12

Around 5% of patients are diagnosed after the age of 18.

Question 13

What are some additional features of cystic fibrosis?

Answer 13

Short stature, diabetes mellitus, delayed puberty, rectal prolapse, nasal polyps, male infertility, and female subfertility.

Question 14

What is the management approach for cystic fibrosis?

Answer 14

Management of cystic fibrosis (CF) involves a multidisciplinary approach.

Question 15

What is a key component of cystic fibrosis management?

Answer 15

Regular (at least twice daily) chest physiotherapy and postural drainage. Parents are usually taught to do this.

Question 16

What dietary recommendation is made for patients with cystic fibrosis?

Answer 16

A high calorie diet, including high fat intake.

Question 17

What should patients with cystic fibrosis do to prevent cross infection?

Answer 17

Minimise contact with each other to prevent cross infection with Burkholderia cepacia complex and Pseudomonas aeruginosa.

Question 18

What type of supplementation is recommended for cystic fibrosis patients?

Answer 18

Vitamin supplementation.

Question 19

What supplements should cystic fibrosis patients take with meals?

Answer 19

Pancreatic enzyme supplements.

Question 20

What is a contraindication to lung transplantation in cystic fibrosis?

Answer 20

Chronic infection with Burkholderia cepacia.

Question 21

What is Lumacaftor/Ivacaftor (Orkambi) used for?

Answer 21

It is used to treat cystic fibrosis patients who are homozygous for the delta F508 mutation.

Question 22

How does lumacaftor work?

Answer 22

Lumacaftor increases the number of CFTR proteins that are transported to the cell surface.

Question 23

What is the function of ivacaftor?

Answer 23

Ivacaftor is a potentiator of CFTR that is already at the cell surface, increasing the probability that the defective channel will be open and allow chloride ions to pass through the channel pore.

Question 24

What was the previous dietary recommendation for cystic fibrosis patients?

Answer 24

Previously high calorie, low-fat diets have been recommended to reduce the amount of steatorrhoea.