Cystic Fibrosis

Question 1

What is cystic fibrosis?

Answer 1

It is a multi system autosomal recessive disorder which results in abnormal ion transport across epithelial cells.

Question 2

1. Which protein is affected in CF?
2. Where is the mutation?
3. What is the most common mutation?

Answer 2

1. CFTR protein is affected, which is a chloride dependant channel on the membrane of cells.
2. The mutation is on chromosome 7.
3. Over 1000 mutations have been shown to cause CF but the most common is F508

Question 3

What systems are affected in CF?

How?

Answer 3

Respiratory system:

• Thick mucous which leads to recurrent respiratory infections and bronchiectasis.
• Often ends with Pseundomonas colonisation.
• The child has a persistent loose cough, productive of purulent sputum.
• With established disease there is finger clubbing and eventually 95% die of respiratory failure.

Pancreatic:

• Ducts get blocked by thick secretions therefore digestive enzymes cannot be released causing absorption issues, streatorrhoea (pale greasy stools), poor growth and weight gain.
• May also eventually develop pancreatitis, diabetes and gallstones due to issues with the pancreas.

Intestines:

• Meconium ileus as neonate (10-20%)
• Distal intestinal obstruction (DIOS) - same as above but in older

Hepatic:

• Liver failure due to chronic blockage of ducts

Reproductive:

• Men are infertile as they are born without a vas deferens

Question 4

How does CF present and how is it diagnosed?

Answer 4

• Usually it is found via screening.
• The heel-prick test for immunoreactive trypsinogen is used to screen for CF shortly after birth.
• If not picked up via screening patient would present with failure to thrive/poor growth, pale diahorea and repeated respiratory infections.
• The child has a persistent loose cough, productive of purulent sputum.
• On examination there is hyperinflation of the chest due to air trapping, coarse Inspiratory crepitations and/or expiratory wheeze.

Question 5

How is CF treated?

Answer 5

Respiratory:

• Physiotherapy twice weekly
• Prophylactic abx (flucloxacillin + rescue abx for exacerbations)
• Mucolytics (hypertonic saline, nebulised DNAse)

Pancreatic:

• Creon (oral enteric coated pancreatic replacement)
• High calorie diet
• Fat soluble vitamin replacement

Note respiratory infections are treated with 14 days intensive IV abx.