The remarkable story of cystic fibrosis (CF) – from gene discovery in 1989 to highly effective precision-medicine therapies today – inspires Christine Kim Garcia, MD, PhD, as she searches for rare mutations in genes linked to inherited forms of lung fibrosis, termed familial pulmonary fibrosis (FPF).
“Cystic fibrosis has provided a framework for approaching the genetics of lung fibrosis,” said Dr. Garcia, Frode Jensen Professor of Medicine and chief of the pulmonology, allergy, and critical care medicine division at Columbia University, and director of the Columbia Precision Medicine Initiative, both in New York.
Pulmonary fibrosis is more complicated than CF. “Mutations in more than 10 different genes can lead to the increased heritable risk of pulmonary fibrosis that we find in families. Different mutations exist for each gene. Sometimes the mutations are so rare that they are only found in a single family,” she said. “In addition, different subtypes of fibrotic interstitial lung disease can be linked to the same mutation and found in the same family.”
Despite these complexities, genetic discoveries in PF have illuminated pathophysiologic pathways and are driving the research that Dr. Garcia and other experts hope will lead to helpful prognostic tools and to precision therapies. And already, at institutions like Columbia, genetic discoveries are changing clinical care, driving treatment decisions and spurring family screening.
Thomas Ferkol, MD, whose research focuses on genetic factors that contribute to suppurative airway diseases such as CF and primary ciliary dyskinesia (PCD), similarly regards CF as a road map for genetics research and genetic testing in practice.
“The treatments we’re doing now for CF are increasingly based on the genetics of the individual,” said Dr. Ferkol, professor and division chief for pediatric pulmonology at the University of North Carolina at Chapel Hill, where the UNC Children’s Hospital hosts a rare and genetic lung disease program. For PCD, genetic testing has become a front-line diagnostic tool. But in the future, he hopes, it will also become a determinant for personalized treatment for children with PCD.
The cystic fibrosis transmembrane conductance regulator (CFTR) gene was the first lung disease gene to be discovered using gene-mapping techniques. Since then, and especially in the last 15-20 years, “there’s been a lot of progress in the identification of genes for which mutations and variations cause specific forms of pulmonary disease, many of which can now establish a firm diagnosis, and some of which lead to very directed changes in management. There has also been great progress in the availability of genetic testing,” said Benjamin A. Raby, MD, MPH, director of the Pulmonary Genetics Center at Brigham and Women’s Hospital, Boston, which sees patients with a host of cystic lung diseases, bronchiectasic lung diseases, fibrotic lung diseases, and other conditions, including pulmonary fibrosis and PCD.
Pulmonary fibrosis in adults and PCD in children are two examples of lung diseases for which genetic discoveries have exploded in recent years, with important implications for care now and in the future.
Leveraging genetic testing in PF
FPF describes families with two or more members with PF within three degrees of relationship; it is a designation believed to affect 20%-25% of people with PF and occurs predominantly later in the adult years (after 50 years of age), most commonly in autosomal dominant fashion, and amidst a stew of genetic risks, environmental exposures, and other insults.
Dr. Garcia and other researchers have uncovered two main types of genes in which rare variants can give rise to a heritable risk of FP: Genes that contribute to the maintenance of telomere length, and genes involved in surfactant metabolism. [Last year, Dr. Garcia and colleagues reported their discovery of both rare and common variants in a “spindle gene,” KIF15, in patients with IPF, suggesting an additional pathogenic pathway. The gene controls dynamics of cell division. (Am J Respir Crit Care Med. 2022;206:p 56-69.)]
Detection of telomere pathway involvement – most commonly involving the TERT gene – is consequential because patients with telomere-associated gene mutations “tend to progress faster and have a more aggressive disease course than patients without these mutations … regardless of how their scans or biopsies look,” as do patients who have short age-adjusted telomere length, said Dr. Chad Newton, MD, who directs the Interstitial Lung Disease program at the University of Texas Southwestern and researches the genetics of ILD.
The future of genetic screening for PF
Future genetic screening approaches for PF may cast an even wider net while better stratifying risk for family members. At Brigham and Women’s Hospital, where family screening was a major impetus for the 2008 founding of the Pulmonary Genetics Center, research published several years ago by Dr. Raby and his colleagues found that 31% of 107 asymptomatic first-degree relatives of patients with PF had interstitial lung abnormalities on chest CTs – whether or not a family history was reported – and 18% had clear radiographic or physiological manifestations of fibrosis (Am J Respir Crit Care Med. 2020;201:1240-8).
“That’s more than 10-fold higher than what we thought we’d see, based on prior literature. … And the numbers were pretty much the same whether or not there was a family history of fibrosis reported by the patient,” said Dr. Raby, also the Leila and Irving Perlmutter professor of pediatrics at Harvard Medical School, Boston, and chief of the division of pulmonary medicine at Boston Children’s Hospital. “We used to think we only needed to worry about genetic risk when there was a family history. But now we see that sporadic cases are also driven by genetics.”
Their study also included a 2-year follow-up chest CT, in which the majority of the screened relatives participated. Of those, 65% who had interstitial changes at baseline showed progression. Four percent of those without interstitial abnormalities at baseline developed abnormalities (Am J Respir Crit Care Med. 2023;207:211-4). “The fact that 65% progressed suggests that in the majority of patients what we’re finding is something that’s real and is going to be clinically meaningful for patients,” he said.
A next phase of research at Brigham & Women’s and Boston Children’s, he said, will address PF’s “complex genetic signature” and test polygenic risk scores for idiopathic PF that take into account not only rare genetic variants that can be solidly linked to disease but many common genetic variants being detected in genome-wide association studies. [By definition, common variants, otherwise known as single-nucleotide polymorphisms (SNPs) occur with greater frequency in the general population (> 5%), generally reside within noncoding regions, and may contribute to disease risk but alone do not cause disease.]
“As technologies and genetic studies improve, we’re seeing we can estimate much better the likelihood of disease than we could 10 years ago,” he said. A “potent” common variant called the MUC5B promoter polymorphism has been shown to confer a 3-fold to 20-fold increased risk for PF, he noted. (Polygenic risk scores are also being developed, he said, for asthma and chronic obstructive pulmonary disease.)
“Every time one sees a patient with PF that is thought to be idiopathic one should start thinking about their at-risk family members, particularly their siblings,” Dr. Raby said. But in doing so, “wouldn’t it be wonderful if we could use polygenic risk scores to assure some [family members] that they’re in the lowest tier of risk and might need pulmonary function studies every 5 years, for example, versus someone we’d want to see more frequently, versus someone [for whom] we’d want to start preventive therapy at the earlier signs of declining lung function?”
Moving forward, he and the others said, the field needs more research to determine how genetic risk factors predict disease progression and prospective clinical trials to test whether long-term outcomes are indeed improved by early institution of antifibrotic therapy and other genetics-driven management decisions. “The data we’re using to inform prognosis and treatment decisions are compelling, but a lot of it is based on cohort studies and retrospective research,” Dr. Newton said.
Multi-institutional transomics studies and other research projects are underway, meanwhile, to build upon gene identifications and learn more about the pathobiology of PF. “We know about two big genetic pathways … but we need to sort it all out,” he said. For instance, “are there intermediate pathways? And where does it actually start? What kind of cell?”
Genetics’ impact on PCD
About 20 years ago, only two genes were linked to PCD, a largely autosomal recessive disorder that results from abnormalities in the cilia and subsequently improper airway clearance. Today, said Dr. Ferkol, there are over 50 known genes that, if defective, can lead to PCD.
“Based on our latest estimates, I’d say we can diagnose people using genetics about 70%, maybe 80%, of the time,” Dr. Ferkol said. Genetic testing has become a first-line diagnostic tool for PCD in North America – a significant development given that a definitive diagnosis has long been challenging, he said.
A genetics-based diagnosis of PCD is sometimes challenged by the finding of variants of unknown significance (VUSs) on genetic testing (often missense mutations) “because some of the genes involved are huge,” noted Dr. Ferkol, who coleads the NIH-funded Genetic Disorders of Mucociliary Clearance Consortium. “But many times, it’s straightforward.”
Children with PCD have repeated or persistent upper respiratory tract infections beginning early in life – like chronic rhinosinusitis or suppurative otitis media – and chronic bronchitis, leading to bronchiectasis. About half of patients have a spectrum of laterality defects, where organs are malpositioned in a mirror image of normal. Some individuals also have cardiac defects, and subfertility in both males and females can frequently occur.
Just as it has become increasingly clear that CF exists as a continuum, with milder and variant forms having been recognized since the advent of genetic testing, “we’re finding genotype-phenotype relationships in PCD,” Dr. Ferkol said. “Certain individuals have more rapid pulmonary decline, which is related in part to their genetics.”
With PCD, “I’m convinced this is a continuum. Some patients have unmistakable, clear-cut PCD, but I’m sure we’re going to find individuals who have milder variants in these PCD-associated genes that lead to milder disease,” he said.
There are no specific treatments that will correct cilia dysfunction, and current therapy options are borrowed from other diseases such as asthma and CF. However, newer treatments targeting specific genetic defects are in early clinical studies. Will the gene discoveries and more research open up new avenues for treating PCD, as happened in CF? Dr. Ferkol hopes so.
Approximately 2,000 genetic variants have been identified in the CFTR gene, though not all are pathogenic. “The newer, highly effective modulators used in CF target a particular CFTR mutation class, so some drugs will work for some people with the disease, but not all,” Dr. Ferkol said. “It’s personalized medicine.”
Modulator therapies designed to correct the malfunctioning proteins made by the CFTR gene have profoundly changed the lives of many with CF, improving lung function and everyday symptoms for patients, allowing them to lead near-normal lives. “It’s astonishing,” he said.
Dr. Garcia reported consulting for Rejuvenation Technologies and Rejuveron Telomere Therapeutics; in addition, her laboratory has received support from Boehringer Ingelheim and Astrazeneca for investigator-initiated research. Dr. Newton reported he has performed consulting for Boehringer Ingelheim. Dr. Ferkol reported involvement in a longitudinal study defining endpoints for future clinical PCD trials funded by ReCode Therapeutics and leadership of an international clinical trial for PCD supported by Parion Sciences. He has received honoraria from the Cystic Fibrosis Foundation and serves as a member of the ReCode Therapeutics PCD Clinical Steering Committee. Dr. Raby reported no relevant disclosures.
This article originally appeared on MDedge.com, part of the Medscape Professional Network.
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Publish date : 2023-09-18 19:20:19
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