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Paediatric Laboratory Medicine

Cystic Fibrosis: CFTR Recurrent Mutations

Clinical Significance

Cystic fibrosis is the most common autosomal recessive disorder among Caucasians of Northern European descent. Symptoms are highly variable between patients, but those with ‘classical’ CF produce thick, sticky mucous that clogs their respiratory airways and lungs. This mucous provides a breeding ground for infections, and subsequent damage of lung tissue, which can result in respiratory and heart failure. The mucous may cause gastrointestinal pseudo-obstructions, block pancreatic and bile ducts and interfere with exocrine function. Cystic fibrosis mutations are associated with male infertility in about 10 per cent of infertility cases.

CF is caused by mutations in the CFTR gene located on chromosome 7. Over 1,300 different mutations in the CFTR gene have been identified. The most common of these, deltaF508, is associated with about 70-72 per cent of the CF chromosomes in Caucasians of Northern European descent. The other CFTR mutations are rare although some of these have a high frequency in certain ethnic groups. To be affected with CF, an individual must have two mutations in the CF gene (one inherited from each parent); these may or may not be identical mutations.

The disease is present when a child receives two copies of a defective gene, one from each parent. Any person with one copy of the defective CFTR gene is a cystic fibrosis carrier. Carriers do not have, and will never develop, cystic fibrosis. However, if two carriers wish to have children, there is a one in four chance (25 per cent) that their baby will be born with cystic fibrosis. There is a three in four chance (75 per cent) that their baby will not have cystic fibrosis.

Within the CFTR gene lies a region, the Intron 8 T-tract, which affects the efficiency of the normal CFTR gene. There are three versions of this tract, which vary between individuals: 9T, 7T and 5T. The low-efficiency 5T variant can be considered a very mild mutation by itself and can increase the severity of other mutations within the same gene. For example, one CFTR mutation coupled with the 5T variant may result in mild symptoms of CF or male infertility.

Test Name

Cystic Fibrosis: CFTR Recurrent Mutations

Alternate Name/ Synonym

  • Congenital Bilateral Absence of the Vas Deferens (CBAVD)
  • CFTR-related hereditary pancreatitis
  • Bronchiectasis
  • Mucoviscidosis

Gene Name

  • CFTR

Test Code

CF

Division

Molecular Genetics

Method

Targeted analysis of 39 recurrent mutations

External Proficiency Testing

CAP

Turn Around Time

2 weeks (Prenatal samples), 2-3 weeks (Pregnancy/Urgent samples), 4-6 weeks (Routine)

Protein

Cystic fibrosis transmembrane conductance regulator

Disease/Condition

Cystic Fibrosis

Specimen Type

Blood; extracted DNA is not accepted for CFTR Deletion/Duplication Analysis.

If sending a prenatal sample, please contact the laboratory prior to sending sample to discuss sample requirements.

For details about specimen requirements, please refer to: Specimen Type & Requirements (PDF). 

Minimum Specimen Requirements

5-10 mL EDTA or ACD 0.5 mL EDTA (neonate); minimum 10 ug in 100 uL low TE (pH8.0)

Storage/Transportation

Room Temperature

Special Requirements

Special Instructions for Genome Diagnostics Samples

If sample shipment >48 hours, ship on ice.

Approval is not required

CPT Codes

81220

Shipping and Contact Information

The Hospital for Sick Children
Rapid Response Laboratory
170 Elizabeth Street, Room 3642
Toronto, ON
M5G 2G3
Canada
Phone: 416-813-7200
Phone: 1-855-381-3212

Interpretation

Interpretation is provided in report

Information Sheet: Cystic Fibrosis