Cystic fibrosis. Sequencing of the whole CFTR gene by Sanger [1 gene]

Cystic fibrosis is the most common lethal autosomal recessive disease among Caucasians. Its incidence is 1:3,200 among Caucasians, 1:10,000 among Latinos, and 1:10,500 among African Americans. It results from mutations in the CFTR gene, which regulates ion transport across the cell membrane, leading to abnormally thick and stringy secretions that obstruct the airways. Typical symptoms include digestive manifestations (recurring pancreatitis, pancreatic failure, intestinal obstruction, and malnutrition), pulmonary manifestations with recurring pulmonary infections, bronchiectasis and decline of the pulmonary function, growth retardation, and male infertility.
The diagnosis of CF requires that both internationally accepted diagnosis criteria are met:

  • Symptoms concordant with CF in one or more organs or positive result in neonatal screening tests or sibling with a cystic fibrosis diagnosis.
  • CFTR gene dysfunction evidenced by an increase in the concentration of chlorine in sweat >60mmol/L or alteration in the nasal transmembrane potential or presence of two mutations related with CF in each of the gene’s alleles.

In addition to its implications for the diagnostic process, family study, and prenatal genetic counselling, testing for mutations in the CFTR gene is crucial for therapeutic decision-making because new CFTR modulators are indicated for patients with specific variants.

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Cystic fibrosis. Sequencing of the whole CFTR gene by Sanger

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Technique: Sanger

Turnaround time (TAT): 25 days

Ref. S-202009880

Cystic fibrosis. Sequencing of the whole CFTR gene by Sanger: View panel

Over 1,500 variants related with the disease in any region of the gene have been described. To develop the disease, there must be a mutation in each one of the parents’ alleles. Two thirds of cases are due to a small group of mutations, but the rest present huge allelic heterogeneity depending on the geographic area and ethnic group. The comprehensive study of variants is not included in panels that are routinely performed. Given that defects can occur in any CFTR region, it is necessary to perform the sequencing of the whole gene, including intronic regions, promoters, and carrying out the study of duplications and deletions (CNV). Also, regarding family planning, the genetic study of CFTR must include the sequencing of the whole gene to minimize the risk of false-negative results and to evaluate the heritability of CF and the possible affectation of descendants. Our basic CF panel performs the whole sequencing of the CFTR gene following current recommendations.

  • CFTR

Priority Genes : Genes where there is sufficient evidence (clinical and functional) to consider them associated with the disease; they are included in the clinical practice guidelines.
Secondary Genes: Genes related to the disease, but with a lower level of evidence or that constitute sporadic cases.
* Candidate Genes: Not enough evidence in humans, but potentially associated with the disease.

References

  1. Farrell PM, Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis. Foundation’s Pediatric. 2017 Feb; 181S:S4-S15.e1. Acuña Quiros.et al. Tratado de fibrosis quística. Sociedad Española de Fibrosis Quística-Ramos.
  2. M.D. Extensive sequence analysis of CFTR, SCNN1A, SCNN1B, SCNN1G and SERPINA1. Suggests an oligogenic basis for cystic fibrosis-like phenotypes. Clin Genet. 2014 Jul;86(1):91-5.
  3. Anita Balázs and Marcus A. Mal. Role of the SLC26A9 Chloride Channel as Disease Modifier and Potential. Therapeutic Target in Cystic Fibrosis. Front. Pharmacol.9:1112
  4. ONeal WK, Knowles MR. Cystic Fibrosis Disease Modifiers: Complex Genetics Defines the Phenotypic Diversity in a Monogenic Disease. Annu Rev Genomics Hum Genet. 2018 Aug 31; 19:201-222.