The numbers are there, indisputable. “Over the whole of France, we observe a slight downward trend in the number of newborns with cystic fibrosis since 2002, the start date of the count of births of children with cystic fibrosis on the whole territorysummarizes Marie-Pierre Audrezet, research engineer at Brest University Hospital and national referent “molecular biology of cystic fibrosis” for neonatal screening. By region, however, this drop is not significant. »
Over the period 2002-2009, the average incidence was one affected child for 4,800 births. It then declined, over 2010-2017, to one child for every 5,800 births. In 2021 alone, the incidence was one child for every 6,150 births. “Average impacts are preferably calculated over periods of five to seven years, to correct for the effect of fluctuations from one year to the next”explains Marie-Pierre Audrezet, these fluctuations being linked to the low incidence of the disease.
Healthy carriers
Since 1994, genetic counseling has been offered to relatives of an affected child. When a couple has a first sick child, their risk of having a new affected child will be 25% for each subsequent pregnancy. This calculation depends on the mode of transmission of the disease. Cystic fibrosis, in fact, is a recessive genetic disease. A child will only develop cystic fibrosis if they carry two mutated copies of the causative gene, the CFTR gene (one on each chromosome 7). He will have inherited one mutated copy from his father and another from his mother, with each parent carrying only one mutated copy. Individuals who carry a single copy of this gene are said to be “healthy carriers”; it is estimated that about one person in 38 is in this case.
When a couple has a first affected child, a genetic investigation is then extended to the family: it is proposed in particular to the brothers and sisters of the parental couple. This work makes it possible to identify other healthy carriers in the family and to screen their spouses, if they wish.
If both members of a couple carry a mutated copy of the CFTR gene, they can benefit, if they wish, from prenatal diagnosis from the twelfth week of pregnancy (by taking a sample from the trophoblast – future placenta) or from fifteenth week of pregnancy (by amniocentesis). “The identification of a fetus carrying cystic fibrosis can justify the use of a medical termination of pregnancy”underlined the High Authority for Health in 2009. As a second intention, some couples may be offered medically assisted procreation followed by preimplantation diagnosis.
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