Genomics in general practice


Cystic fibrosis
☰ Table of contents


Practice point


The commonly used newborn screening tests will identify 85–90% of individuals with cystic fibrosis (CF), but will not identify individuals with rare (atypical) CF variants. 1 Such patients may present to the general practitioner (GP).

 


What do I need to know?


CF is the most common life threatening genetic condition in Australia. CF primarily affects the lungs and digestive system, which become obstructed with excessive, thick mucus. It is a condition that follows an autosomal recessive inheritance pattern, meaning both parents must carry a CF-causing gene variants to be at risk of having a child with the disease.

About one in 25 Australians of northern European ancestry are carrierof the CFTR gene variant. The most common variant in the CFTR gene is the ΔF508 variant, which accounts for approximately 70% of all CFTR gene variant in those of northern European ancestry. While there are more than 2000 variants in the CFTR gene, around 40 variants contribute to approximately 90% of cases of CF in Australia.1,2


Genetic testing


Almost all babies in Australia are screened at birth for CF. There are some who may be lost to follow up or refuse to consent for screening. Exact numbers in Australia are not available. Refer to ‘Newborn screening’ for more information.

Carrier screening for CF can be offered by GPs to all couples planning a pregnancy (or already pregnant), regardless of family history or ethnicity. Refer to ‘Reproductive carrier screening’ for more information.

Carrier screening for CF is also available through some genetic screening programs for at-risk groups (eg people of Ashkenazi Jewish ancestry) and through commercial carrier screening tests.1


When should I refer?


Couples who are CF carriers should be referred for genetic counselling if they are planning a pregnancy or in the first trimester of pregnancy.3

Children suspected of having CF (who have not been previously identified through newborn screening tests) should be referred to a paediatrician for a sweat test. Symptoms may include recurrent cough, failure to thrive, lower respiratory tract infection, bronchiectasis and/or rectal prolapse.

Males presenting with infertility due to congenital bilateral absence of the vas deferens (CBAVD) may have an atypical form of CF. Refer the patient to a fertility specialist.4 


Other considerations


Cascade screening should be offered following a diagnosis of CF in the family to identify other potential carriers.1

 

Resources for patients


Information

National Library of Medicine, Cystic fibrosis

Better Health Channel, Cystic fibrosis

Centre for Genetics Education, Fact sheet 41: Cystic fibrosis

Support

Cystic Fibrosis Australia


Genomics in general practice




 

 

  1. Delatycki MB, Burke J, Christie L, et al. Human Genetics Society of Australasia. Position statement: Population-based carrier screening for cystic fibrosis. Twin Res Hum Genet 2014;17(6):578–83.
  2. Cystic Fibrosis Foundation. The clinical and functional translation of CFTR (CFTR2). Baltimore, MD: Johns Hopkins University, 2011. [Accessed 15 December 2017].
  3. he Royal Australian College of General Practitioners. Guidelines for preventive activities in general practice. 9th edn. Melbourne: RACGP, 2016. Available at  [Accessed 15 December 2017].
  4. Ong T, Marshall SG, Karczeski BA, et al. Cystic fibrosis and congenital absence of the vas deferens. GeneReviews. Seattle, WA: University of Washington, 2001. [Accessed 15 December 2017].

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