La cystic fibrosis, Also called cystic fibrosis, is a genetic disease that manifests itself mainly by respiratory and digestive symptoms.

It is the most frequent genetic disease in populations of Caucasian origin (incidence of approximately 1/2500).

Cystic fibrosis is caused by a mutation in a gene, the CFTR gene, which causes a dysfunction of the protein CFTR, involved in the regulation of the exchanges of ions (chloride and sodium) between the cells, in particular at the level of the bronchi, the pancreas, the intestine, the seminiferous tubes and the sweat glands . Most often, the most severe symptoms are respiratory (infections, difficulty in breathing, excessive mucus production, etc.), pancreatic and intestinal. Unfortunately, there is currently no curative treatment, but early treatment improves quality of life (respiratory and nutritional care) and preserves organ function as much as possible.

This disease is potentially serious from childhood and requires early management. It is for this reason that in France, all newborns benefit from screening for cystic fibrosis, among other conditions. In Canada, this test is only offered in Ontario and Alberta. Quebec has not implemented systematic screening.

The test is carried out as part of the screening for various rare diseases at the 72st hour of life in newborns, from a blood sample taken by pricking the heel (Guthrie test). No preparation is necessary.

The drop of blood is placed on special filter paper, and dried before sending to a screening laboratory. In the laboratory, an immunoreactive trypsin (TIR) ​​assay is performed. This molecule is produced from trypsinogen, itself synthesized by the pancreas. Once in the small intestine, trypsinogen is transformed into active trypsin, an enzyme that plays a role in the digestion of proteins.

In newborns with cystic fibrosis, trypsinogen has difficulty reaching the intestine because it is blocked in the pancreas by the presence of abnormally thick mucus. Result: it passes into the blood, where it is transformed into “immunoreactive” trypsin, which is then present in abnormally high quantities.

It is this molecule that is detected during the Guthrie test.

If the test shows the presence of an abnormal amount of immunoreactive trypsin in the blood, the parents will be contacted to have the newborn baby undergo further tests to confirm the diagnosis of cystic fibrosis. It is then a question of detecting the mutation (s) of the gene CFTR.

A so-called “sweat” test can also be performed to detect high concentrations of chlorine in the sweat, characteristic of the disease.