Lung function in children with cystic fibrosis in the USA and UK
Why did this study happen?
Understanding how other countries treat CF and what impact this has is important to ensure people with CF in the UK have the best possible physical health. We can then look to see what lessons can be learned from these international comparisons and analysis. This is why we have been working with the Cystic Fibrosis Foundation (CFF) for a long time to explore and understand any differences between the two countries.
It was back in 2015 when a group of researchers first released some data comparing the CF populations in the UK, with the US that kick-started this publishing a new analysis this week. They found that children aged under 12 in 2010 in the UK had worse lung function than people with CF the same age in the US. The researchers weren’t sure why this might be, and recommended that a long-term analysis assessing differences over time, rather than in just one year, was needed to find out if the difference was ‘real’, or to do with differences in the Registry data between the two countries.
What is the study?
After receiving funding from the Cystic Fibrosis Trust, UK researchers have once again teamed up with experts from the US to do just that, and the research has now been released. The study focused on the health status of children aged 6-17 years old with cystic fibrosis in the years 2003 – 2014. As a way of making sure they were comparing ‘like with like’, only data from people homozygous for the F508del mutation was used. For those people who had had a transplant, the study only considered data up to the point at which they had their transplant. Therefore, the results may not be applicable to people older than 17, who have had a transplant, or who have a different genotype than homozygous F508del.
What are the results?
The results confirmed that on average lung function was higher in children living in the US compared to the UK. At the age of 17, that difference was approximately 5.0% FEV1% predicted. The exact percentage changes depending on calendar time, the mathematical model used, and whether men, women, or both are the focus. The research did show that the UK compared favorably to the US when it comes to nutritional outcomes and rates of an infection called S. aureus (sometimes called ‘staph’).
The researchers considered whether the results could be an artefact of differences between the Registries. For example, the US collected more frequent information on lung function than the UK during the study period. So, on average the US analysis had 24 measurements to go off, whereas the UK only had 4. However, the authors carefully considered other research and analysis and felt that this did not explain the differences in lung function that they found.
What does it mean?
The authors felt that the UK results might be because fewer people with CF were prescribed hypertonic saline and/or DNase at a young age compared to the US. The more aggressive mucolytic therapy in the US might have prevented exacerbations and preserved lung function better, even though the nutritional status of children in the UK was better.
It’s important to remember that these results might not apply to the adult CF population, or affect health outcomes for people aged over 18 here in the UK. CF Registry Annual reports using 2015-2019 data show that the median predicted age of survival based on UK CF Registry data was 49.1, compared to 46.2 in the US.
A lot has changed since 2014, which is when the study ended. CFTR modulators are now available in both the US and the UK to nearly everyone homozygous for the F508del mutation. However, the suggestion by the researchers that early aggressive prescribing of effective medicines may improve lung function makes it clearer than ever than access needs to be cascaded down to younger ages as soon as possible. This study is a reminder that lung problems begin early in people with CF and medicines that have been found to be safe and effective, and have been approved, should be started early in life in order to maintain lung health in children. Find out the latest on the Trust’s campaign for Access to Medicines.
The new modulator therapies work by restoring the normal fluid levels in the lung. Many adults who start modulators talk about the purge, or clearing, of sticky secretions they experience. It is therefore possible nebulised ‘mucolytics’ are no longer needed in people taking highly effective modulators. The Trust is also funding and supporting a national study designed to look at what difference taking hypertonic saline and DNase makes once someone is taking a CFTR modulator medicine. This large-scale clinical trial, called 'CF STORM' is due to launch, fully integrated with the UK CF Registry, this summer.
This type of study is only possible because of the participation of people with CF and their care teams in Registries around the world, and because of close collaboration between patient organisations like the Trust and the Cystic Fibrosis Foundation. Because this information is readily available for research, we can discover differences and work to better understand them. The authors have recommended that more work is needed to investigate why this gap in lung function is present, with a focus on analysis of treatment patterns.
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