The rate of new cases, or incidence, of cystic fibrosis (CF) has been declining gradually and every year in the United States and Canada — and has been for nearly a quarter of a century — according to a new study.
From 1995 to 2019, the incidence of cystic fibrosis fell at a rate of 1.6% per year in both countries, according to the data. Notably, however, these rates varied considerably from region to region within each country.
The findings may be explained by increased population diversity in North America, as well as factors related to genetic testing influencing family planning decisions, the researchers noted.
“Reporting incidence rates along with the rate of change over time can provide important information for future planning to ensure adequate resources to care for the CF community,” the team wrote.
Improved detection and treatment of cystic fibrosis
The study, “Contemporary incidence rates of cystic fibrosis in Canada and the United Stateswas published in the Cystic Fibrosis Diary by a team of researchers from both countries.
Cystic fibrosis is caused by mutations in both copies of the CFTR gene – one inherited from each biological parent – that provides cells with the instructions to build a protein of the same name. People who carry only one mutated copy, called cystic fibrosis carriers, do not develop the disease, but can pass the mutation on to their children.
The United States is among the countries with the highest incidence of cystic fibrosis, with nearly 40,000 children and adults living with the disease. Cystic fibrosis has been reported to affect one in 4,000 live births in the United States and one in 3,600 live births in Canada.
Thanks to advances in treatment, more CF patients are surviving into adulthood, and more than half of people with CF are now 18 or older. By 2040, it is estimated that nearly three-quarters of CF patients in the United States will be adults.
While these statistics may help explain the increase in the total number of people with cystic fibrosis worldwide, the number of new cases appears to be decreasing, at least in some countries. Researchers say this may be due to several factors, including genetic testing and newborn screening.
On the one hand, the availability of CF carrier screening, genetic counseling and preimplantation genetic testing may reduce the number of babies born with CF. Preimplantation genetic testing examines embryos generated by in vitro fertilization for the presence of the defect CFTR gene before being transferred into the mother’s womb.
On the other hand, although the widespread implementation of newborn screening (NBS) for cystic fibrosis has been associated with better outcomes for people born with the genetic disease, it may affect the decision of couples who are at risk of having a another child with cystic fibrosis to become pregnant. Again. Some parents may also choose genetic testing before having more children.
Additionally, “increasing immigration rates to North America could influence CF birth rates, as individuals from regions such as Asia, India, the Middle East, and Africa would have lower rates of carriers of the cystic fibrosis transmembrane regulatory protein (CFTR) mutation than in Europe. offspring,” the researchers wrote.
According to the team, knowing how the landscape of cystic fibrosis is changing can help healthcare professionals and policymakers design and implement care and treatment programs for people born with the disease.
“This information is important for resource planning and for monitoring how programs (for example, genetic counselling, [CFTR] availability of modulators, etc.) may impact the incidence of CF in the future,” they wrote.
To estimate cystic fibrosis incidence rates in the United States and Canada over nearly 25 years — as well as to detect changes over time — the researchers relied on data from the CF Patient Registry Foundation and the Canadian CF Registry. They also removed publicly available national vital statistics databases in both countries.
Between 1995 and 2019, 21,356 people were born with CF in the United States and 2,478 in Canada.
After taking into account the implementation of newborn screening and delayed diagnoses of cystic fibrosis, the estimated incidence rate of cystic fibrosis in 2019 in the United States was one in 5,078 people. In Canada, the incidence cystic fibrosis was one in 3,848. These represent lower incidence rates than those historically reported for both countries, but are comparable to those reported for central European countries, the team noted.
The incidence of cystic fibrosis varies by region
During this period, the incidence of cystic fibrosis decreased by 1.6% per year in both countries. Assuming this trend continues, researchers predict that 515 people will be born with CF in the United States in 2025; by 2030, that number will drop to 474. In Canada, forecasts indicate that there will be 79 people born with CF in 2025 and 73 five years later.
Notably, incidence rates by region varied “considerably across Canada and the United States,” the team wrote. Specifically, rates ranged from one in 3,000 to one in 6,925 live births in 2019.
Cystic fibrosis was most common in New England and the so-called Mid-Northwest region — a cluster of Midwestern states — in the United States. In Canada, it was most common in the Atlantic region and in Quebec. Overall, the incidence of cystic fibrosis was highest in Atlantic Canada, the data showed.
Most patients with cystic fibrosis were of European ancestry, and their proportion was lower in areas where cystic fibrosis was less common. This may occur not only because of the higher carrier rate of cystic fibrosis among people of European ancestry, but also because non-white people “in these areas have undiagnosed cystic fibrosis because NBS panels are biased towards mutations found in the European population,” the team wrote. .
“Interestingly, the incidence of cystic fibrosis was higher in Canada than in the United States, which may reflect a variety of factors, including differences in carriage rates among different ethnic populations,” writes the researchers.
The data also highlighted that “the relative birth rate is increasing in the U.S. population not identified as white and decreasing in the white population… Meaning that overall the population is becoming more diverse,” the team wrote. .
“However, cystic fibrosis incidence is declining across all racial groups, suggesting that this diversity does not fully explain the decline in cystic fibrosis incidence in the United States,” they added.
The observed progressive reduction in the incidence of cystic fibrosis “could be explained by the differential impact of factors that may influence family planning decisions, such as genetic counseling, carriage testing or preimplantation genetic testing. in both countries, although this requires targeted research to confirm this hypothesis”. the team wrote.
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