The figures are there, indisputable. “Over the whole of France, we have observed a slight downward trend in the number of newborns with cystic fibrosis since 2002, when counting births of children with the disease began throughout the country,” summarized Marie-Pierre Audrezet, research engineer at the Brest Centre Hospitalier Universitaire and national advisor of “molecular biology of cystic fibrosis” for neonatal screening. “By region, however, this decrease is not significant.”
From 2002-2009, the average incidence was one affected child per 4,800 births. It then declined from 2010-2017 to one child per 5,800 births. In 2021 alone, the incidence was one child per 6,150 births. “We prefer to calculate average incidences by periods of five to seven years, to correct the effect of fluctuations from one year to the next,” explained Marie-Pierre Audrezet, these fluctuations being linked to the low incidence of the condition.
Healthy carriers
Since 1994, genetic counseling has been offered to relatives of an affected child. When a couple has a first affected child, their risk of having another affected child will be 25% for each subsequent pregnancy. This calculation is due to the mode of transmission of the condition. Cystic fibrosis, in fact, is a recessive genetic disease. A child will only develop cystic fibrosis if they carry two mutated copies of the offending gene, the CFTR gene (one on each chromosome 7). They will have inherited one mutated copy from their father and one from their mother, with each parent carrying only one mutated copy. Individuals who carry only one copy of this gene are called “healthy carriers”; it is estimated that regarding one in 38 people are in this situation.
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When a couple has a first affected child, a genetic investigation is then carried out on the wider family: it is offered to the siblings of the parental couple. This work makes it possible to identify the other healthy carriers in the family and to screen their spouses, if they so wish.
If both members of a couple carry a mutated copy of the CFTR gene, they can benefit, if they wish, from a prenatal diagnosis as early as the twelfth week of pregnancy (by sampling the trophoblast – future placenta) or the fifteenth week of pregnancy (by amniocentesis). “The identification of a fetus carrying cystic fibrosis may justify carrying out a medical abortion,” stated the Haute Autorité de Santé in 2009. As a second option, some couples may be offered medically assisted reproduction followed by a pre-implantation diagnosis.
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