Cystic Fibrosis: CFTR Gene Sequencing
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Name
Cystic Fibrosis: CFTR Gene Sequencing
Test Code
JK
Indication
Testing is indicated for:
  • Patients suspected to have a mutation to the CFTR gene and who tested negative using the common mutation panel.
  • Family members of an affected individual at risk to be carriers of CF.
CPT Codes
81223 (x1)
Turn around time
4 weeks
This test can be found on the following requisition form(s):

Comprehensive Molecular Test Requisition Form

Metabolic/Newborn Screening Follow-up Test Requisition Form


To order this test online, click the link below:

Order this test online

Submit only 1 of the following specimen types
Preferred specimen type: Whole Blood
Type Specimen Requirements Specimen Collection and Shipping
Whole BloodIn EDTA (purple top) or ACD (yellow top) tube:
Infants (<2 years): 2-3 ml
Children (>2 years): 3-5 ml
Older Children & Adults: 5-10 ml
Refrigerate until time of shipment. Ship sample within 5 days of collection at room temperature with overnight delivery.
SalivaOrageneTM Saliva Collection kit (available through EGL) used according to manufacturer instructions.Store sample at room temperature. Ship sample within 5 days of collection at room temperature with overnight delivery.
Condition Description

Cystic fibrosis (CF) is a chronic genetic condition involving multiple organ systems [1]. Classical CF primarily involves the respiratory and digestive systems, and may have a range of clinical severity. Pulmonary symptoms often include lower airway inflammation, chronic cough, chronic sinusitis, and recurrent infections. Digestive symptoms often include meconium ileus, pancreatic insufficiency resulting in malabsorption and/or failure to thrive, diabetes mellitus, and hepatobiliary disease. Congenital bilateral absence of the vas deferens (CBAVD) is seen in men without pulmonary or digestive symptoms of CF, and results in azoospermia [2]. CBAVD is a significant cause of male infertility.

CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Individuals with mutations in the CFTR gene may also present with milder or atypical symptoms such as pancreatitis or chronic sinusitis.

The incidence of CF is approximately 1 in 3200 live births among Caucasians and is inherited in an autosomal recessive pattern. The carrier frequency is estimated to be approximately 1 in 22-28 in the Caucasian population, 1 in 29 in the Ashkenazi Jewish population, 1 in 60-65 in the African American population, 1 in 46 in the Hispanic population and 1 in 90 in the Asian population.

Initial evaluation and screening of patients for CFTR mutations is accomplished through a panel of 23 common mutations as recommended by the American College of Medical Genetics Subcommittee on Cystic Fibrosis [3] and the American College of Obstetrics and Gynecologists [4]. The detection rate of this panel depends on the patient''''s ethnicity.

When the common mutation panel is negative and mutations to the CFTR gene are suspected, sequencing of the entire gene is recommended to detect rare mutations. For patients with mutations not identified by full gene sequencing, a separate deletion/duplication assay is available using a targeted CGH array (JL).

Click here for the GeneReviews summary on this condition.

References
1. Moskowitz et al. CFTR-related disorders (2005). www.genetests.org
2. Xu et al. Cystic fibrosis transmembrane conductance regulator is vital to sperm fertilizing capacity and male fertility (2007). PNAS 104(23):9816-21.
3. Watson, M. et al. Cystic Fibrosis population carrier screening: 2004 revision of the American College of Medical Genetics mutation panel (2004). Genet Med 6(5):387-91.
4. ACOG Committee Opinion. Update on Carrier Screening for Cystic Fibrosis (2005). Obstetr Gynecol 106:1465-8.
5. Strom et al. (2003) Extensive sequencing of the cystic fibrosis transmembrane regulator gene: assay validation and unexpected benefits of developing a comprehensive test. Genet Med 5(1):9-14.
6. Chevalier-Porst (2005) Identification and Characterization of Three Large Deletions and a Deletion/Polymorphism in the CFTR Gene. Hum Mut Mutation in Brief #806 Online
7. http://www.genet.sickkids.on.ca/

Genes
Methodology
PCR amplification of 27 exons contained in the CFTR gene is performed on patient genomic DNA. Direct sequencing of amplification products is performed in both the forward and reverse directions using automated fluorescence dideoxy sequencing methods. Patient gene sequences are compared to a normal reference sequence. Sequence variations are then classified as mutations, benign variants unrelated to disease or variations of unknown clinical significance. Variants of unknown clinical significance may require further studies of the patient and/or family members. This assay does not interrogate the promoter region, deep intronic regions or other regulatory elements. Large deletions are not detected by this analysis. 
Detection
The detection rates for this assay, as with the common mutation panel, varies in different racial/ethnic groups.
Clinical Sensitivity: 97 - 98% [5, 6, 7].
Analytical Sensitivity: ~99%

Results of molecular analysis must interpreted in the context of the patient''''s clinical phenotype.
Related Tests
  • CF common mutation panel (CF).
  • Ashkenazi Jewish Carrier Panel is available to screen for the panel of 9 autosomal recessive conditions common in individuals of Ashkenazi Jewish background.
  • Custom diagnostic mutation analysis (KM) is available to family members if mutations are identified by sequencing.
  • A deletion/duplication assay is available separately for individuals where mutations are not identified by sequence analysis. Refer to the test requisition or contact the laboratory for more information.
  • Prenatal testing is available for known familial mutations only. Please call the Laboratory Genetic Counselor before collecting a fetal sample.
Special Instructions

Completion of the cystic fibrosis common mutation panel should be completed PRIOR to CFTR gene sequence analysis.

Submit copies of diagnostic biochemical test results (i.e. sweat test results) with the sample, if appropriate. Contact the laboratory if further information is needed.

Sequence analysis is required before deletion/duplication analysis by targeted CGH array. If sequencing is performed outside of Emory Genetics Laboratory, please submit a copy of the sequencing report with the test requisition.