Rate of New CF Cases in US, Canada, Has Dropped for 25 Years: Study

Incidence of cystic fibrosis decreasing 1.6% each year in both countries

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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The rate of new cases, or incidence of cystic fibrosis (CF) is gradually and annually decreasing in the U.S. and Canada alike — and has been for nearly a quarter of century — a new study found.

From 1995 to 2019, CF incidence has dropped at a rate of 1.6% per year in both countries, the data showed. Notably, however, these rates varied widely across regions within each country.

The findings may be explained by increased population diversity in North America, as well as genetic testing-related factors influencing family planning decisions, the researchers noted.

“Reporting incidence rates as well as 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.

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The study, “Contemporary cystic fibrosis incidence rates in Canada and the United States,” was published in the Journal of Cystic Fibrosis by a team of researchers from both countries.

CF is caused by mutations in both copies of the CFTR gene — one inherited from each biological parent — that provides cells with the instructions for building a protein of the same name.  People carrying only one mutated copy, called CF carriers, do not develop the disease, but can pass the mutation on to their children.

The U.S. is among the countries with the highest occurrence of CF, 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 U.S. and one in 3,600 live births in Canada.

With advances in treatment, more CF patients are surviving well 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 U.S. will be adults.

While those statistics may help explain the rise in the total number of people globally with CF, the number of new cases seems to be decreasing — at least in some countries. Researchers say this may be due to several factors, most notably genetic testing and newborn screening.

On one hand, the availability of CF carrier screening, genetic counseling, and pre-implantation genetic testing may reduce the number of babies born with CF. Pre-implantation genetic testing screens embryos generated by in-vitro fertilization for the presence of the faulty CFTR gene before they are transferred into the mother’s womb.

On the other hand, while widespread implementation of newborn screening (NBS) for CF has been linked to better outcomes for those born with the genetic disease, it can affect the decision of couples who are at risk of having another child with CF to become pregnant again. Some parents also may choose genetic testing before having subsequent children.

Additionally, “increased immigration rates to North America could influence birth rates of CF because individuals from regions such as Asia, India, Middle East, and Africa reportedly have lower carrier rates of the cystic fibrosis transmembrane regulator protein (CFTR) mutation than those of European descent,” the researchers wrote.

According to the team, knowing how the CF landscape is changing may help healthcare professionals and policy makers to design and implement programs for the care and treatment of those born with the disease.

“This information is important for resource planning and for tracking how programs (e.g., genetic counselling, [CFTR] modulator availability etc.) may impact the incidence of CF moving forward,” they wrote.

To estimate the incidence rates for cystic fibrosis in the U.S. and Canada spanning nearly 25 years — as well as to detect changes over time — the researchers drew from data from the CF Foundation patient registry and the Canadian CF registry. They also culled publicly available national vital statistics databases in both countries.

Between 1995 and 2019, there were 21,356 people were born with CF in the U.S. and 2,478 in Canada.

After accounting for newborn screening implementation and delayed CF diagnoses, the estimated incidence rate for cystic fibrosis in 2019 in the U.S. was one in 5,078 people. In Canada, CF incidence 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.

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Cystic fibrosis incidence varies by region

During this period, CF incidence decreased by a rate of 1.6% per year in both countries. Assuming the continuation of this trend, the researchers predict 515 people will be born with CF in the U.S. in 2025; in 2030, this number will drop to 474. In Canada, the predictions indicate there will be 79 people born with CF in 2025 and 73 five years later.

Notably, the incidence rates by region varied “dramatically across Canada and the US,” the team wrote. Specifically, the rates ranged from one in 3,000 to one in 6,925 live births in 2019.

CF was most common in New England and the so-called West North Central region — a cluster of Midwestern states — in the U.S. In Canada, it was most common in the Atlantic region and Quebec. Overall, cystic fibrosis incidence was highest in the Atlantic region of Canada, the data showed.

Most CF patients were of European ancestry, and their proportion was lower in regions where CF was less common. This may occur not only due to the higher rate of CF carriers among people of European ancestry, but also because non-white people “in those regions have undiagnosed CF as NBS panels are biased towards mutations found in the European population,” the team wrote.

“Interestingly, the incidence of CF was higher in Canada compared to the US which may reflect of a variety of factors including differences in carrier rates amongst different ethnic populations,” the researchers wrote.

The data also highlighted that “the relative birth rate is increasing in the US population not identified as white and is decreasing in the white population … Meaning that overall, the population is becoming more diverse,” the team wrote.

“However, the incidence of CF is decreasing across all racial groups suggesting that this diversity does not fully explain the decreasing incidence of CF in the US,” they added.

The observed gradual reduction in CF incidence “could be explained by differential impact of factors that may influence family planning decisions such as genetic counselling, carrier testing or pre-implantation genetic testing in the two countries although this needs targeted research to confirm this hypothesis,” the team wrote.

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