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About CF » CFTR mutations » The correlation between CFTR mutations and disease severity

The correlation between CFTR mutations and disease severity

Cystic fibrosis symptoms are highly varied among individual patients, even between siblings who carry identical CFTR alleles. This variation is thought to be influenced by non-genetic factors and modifier genes:1

  • Non-genetic factors include environmental factors (e.g. air quality), level of care, nutritional status and age of onset of lung infection2
  • Modifier genes are thought to interact with CFTR mutations to influence disease severity. For example, reduced amounts of the immune protein mannose-binding lectin (MLB2) is associated with increased rates of CF-related bronchiectasis, which is in part due to earlier colonisation of Pseudomonas aeruginosa in the lung3


This diagram shows the relationship between the type of CFTR gene mutation (genotype) and CF disease severity (or phenotype). For example, certain ‘mild’ CFTR mutations may have increased risk to particular pulmonary conditions such as asthma.4 Patients with ‘severe’ CFTR mutations present with classical CF symptoms.4 This diagram, however, does not take environmental factors into consideration. [Modified from Zielenski.5]


What factors influence CF disease severity?

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  1. Rowntree R & Harris A. Ann Hum Genet 2003;67:471–85
  2. Cutting GR. Ann NY Acad Sci 2010;1214:57–69
  3. Chalmers JD et al. Glycobiology 2011;21:271–82
  4. Bombieri C et al. J Cyst Fibros 2011;10(Suppl 2):S86–102
  5. Zielenski J. Respiration 2000;67:117–33