Cystic Fibrosis: CFTR Sequencing

Clinical Information

Cystic fibrosis (CF) is a common autosomal recessive disorder that affects many functions of the body such as respiration, endocrine function, and reproduction. Although great strides in treatment have increased the length and quality of life for CF patients, it is nearly always fatal by the fourth decade of life. Sweat chloride testing remains the gold standard for diagnosis of CF, however DNA analysis is indicated not only for CF patients but also for their extended families.

In addition to providing information about the specific variants that cause CF, molecular testing allows rapid detection of cystic fibrosis carriers and can determine if the patient has a pancreatic sufficient or insufficient type of the disease. This information plays a large role in clinical management of the affected individual. Over 2,000 variants have been reported in the CFTR gene. The carrier rates of the disorder are 1/25 Caucasians, 1/60 African-Americans, 1/46 Hispanics, 1/90 Asians, and 1/29 in the Ashkenazi Jewish population.

Technical Information

• This test is performed by Sanger sequencing.
• Genomic DNA is used to amplify all coding exons and a region of intron 22 of the CFTR gene by polymerase chain reaction, and each amplified product is sequenced using the Sanger dideoxy method.
• This method can also identify the polypyrimidine tract (5/7/9T) in intron 9, analysis of which will only be routinely performed when the p.R117H pathogenic variant is detected.

Specimen Requirements

• The preferred sample type is 3-4 ml of peripheral blood collected in an EDTA (purple top) tube. Dried blood spots, extracted DNA, and saliva are also accepted for this test. Blood and saliva kits are available by request.
• Approximately 75 µL of blood should be applied to each of the five circles on a filter paper dried blood spot card. Allow blood to dry for at least 4 hours before shipping.
• Send approximately 5 µg of extracted DNA at a requested concentration of 90-130 ng/µl.
• Saliva samples must be submitted in an approved saliva kit.

Transport Instructions

• The blood specimen should be kept at room temperature and delivered via overnight shipping. If shipment is delayed by one or two days, the specimen should be refrigerated and shipped at room temperature. Do not freeze the specimen. Samples collected on Friday can be safely designated for Monday delivery.
• DBS cards should be shipped at room temperature.
• Extracted DNA should be sent at room temperature via overnight delivery.
• Saliva is stable at room temperature and can be delivered via overnight or ground shipping.