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 the fulfilment of the following two internationally accepted diagnostic criteria:

  • Symptoms consistent with CF in one or more organs, positive neonatal screening, or sibling diagnosed with cystic fibrosis.
  • Dysfunction of the CFTR gene evidenced by an increase in chloride concentrations in sweat 60 mmol/L, altered nasal transmembrane potential, or presence of two CF-related mutations in each one of the alleles of this gene.

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.

BASIC CYSTIC FIBROSIS PANEL [1 gene]

CFTR

More than 1500 variants related to the disease have been described in the whole gene. Disease development requires the presence of mutations in both the paternal and maternal allele. While two thirds of the cases are due
to a small number of mutations, the remaining portion shows a wide allelic heterogeneity among geographical areas and ethnic groups, which are not routinely included in panels. Since they can occur in any region of CFTR, the whole gene must be sequenced, including intronic regions and promoters, and duplications and deletions must be analyzed.

When testing the partner of a patient or carrier, the whole gene must be sequenced to minimize the risk of their
progeny being affected by the disease.

Our basic CF panel includes the sequencing of the whole CFTR gene, following current recommendations.

EXTENDED CYSTIC FIBROSIS PANEL [8 genes]

CFTR SCNN1A SCNN1B SCNN1G SERPINA1
SLC26A9 MBL2 TGFB1

In CF, symptoms vary among patients, even among those with identical mutations. This variability is due to the influence of environmental factors and to the action of modulator genes. These genes affect phenotypic expression of the disease, composition and viscosity of secretions, susceptibility to specific infections, decline of pulmonary function, and response to drugs.

We offer an extended panel that includes modulatory genes, as well as other genes associated with overlapping phenotypes.

References

  1. Farrell PM, Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis. Foundation’s Pediatric. 2017 Feb; 181S:S4-S15.e1.
  2. Acuña Quiros.et al. Tratado de fibrosis quística. Sociedad Española de Fibrosis Quística-Ramos
  3. 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.
  4. 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
  5. O’Neal 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.