Cystic Fibrosis

I went to a talk about cystic fibrosis (CF) and the CF  unit at Frimley Park Hospital a few weeks ago given by Dr. Timothy Ho. I hadn’t previously known much about cystic fibrosis and this talk inspired me to do some research and find out more about the disorder.

Cystic fibrosis is an inherited metabolic multi-system disorder. It is characterised by abnormality of chloride and sodium transport across an epithelium, leading to thick, tenacious secretions. It affects most critically the lungs, and also the pancreas, liver, and intestines.

 

CF was previously thought of as a children’s disease and 50 years ago CF patients wouldn’t live to the age of 9. It is the most common lethal inherited genetic disorder in the UK with approximately 7000 UK CF patients. It is also statistically more prevalent in males than in females. It is more common in Caucasians and less common in Asians and Orientals.

Cause

Cystic Fibrosis is caused by mutation in the gene, cystic fibrosis transmembrane conductance regulator (CFTR) in chromosome 7. It could be one of many mutations. This is a recessive gene so only people carrying 2 of these abnormal genes are affected by CF. The abnormality leads to sweat ducts being impermeable to chloride ions.

Also, 25% of CF patients develop diabetes. A little benefit for them is that they don’t have to pay for prescriptions and although that does not make it worth it, they save hundreds of pounds as they have to take many tablets everyday for the rest of their lives.

Symptoms

  • Symptoms often appear in infancy and childhood, such as bowel obstruction due to meconium ileus in newborn babies
  • Salty sweat
  • Poor growth and poor weight gain despite a normal food intake
  • Accumulation of thick, sticky mucus
  • Malabsorption – Abnormal stool
  • Rectal prolapse and constipation
  • Frequent chest infections and coughing or shortness of breath
  • Males can be infertile due to congenital absence of the vas deferens

 Diagnosis

  • Age of diagnosis:
    • 50% by 1 year
    • 90% by 10 years
    • 99% by 20 years
  • Methods:
    • Before birth or after by genetic testing – genotyping of patient, looking for known mutations
    • Immunoreactive trypsinogen (IRT) testing in newborns – a high level of IRT suggests possible CF and requires further testing.
    • Sweat test in early childhood – sweating is induced by pilocarpine iontophoresis and the sweat is tested to determine the sodium and chloride concentrations.

Treatment

Survival improves year on year.

  • Intravenous antibiotics to prevent and treat lung and sinus infections
  • Lung transplantation – both lungs have to be replaced otherwise the one not replaces would infect the new one
    • Only 160 lung donors in the UK annually
    • 10% of lung transplant patients die
    • High concentration of salt solutions (hypertonic saline)

New treatments are being developed for specific mutations. In the UK gene therapy aims to introduce normal CFTR using a viral vector. In the USA medicines are being developed to make the abnormal CFTR work as normal would. This is only available for 2 of the known mutations and therefore less than 5 % of CF patients.

 

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