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[1]: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.
Dr. Chad Newton
Dr. Newton and Dr. Garcia advise patients with PF and a positive family history to undergo panel-based genetic sequencing, along with telomere length measurement. They also advise that undiagnosed first-degree relatives consider what’s called “cascade testing” – genetic sequencing for any pathogenic or likely pathogenic rare variants found in the patient’s investigation. (Dr. Garcia, who cochairs a National Institutes of Health–funded interstitial lung disease curation panel, said she finds evidence of a pathogenic or likely pathogenic variant in about 25% of patients with a family history of PF.)
“We can use this genetic information to consider starting early [antifibrotic] treatment to try to delay progression … just as we would with other forms of pulmonary fibrosis,” Dr. Newton said, “and to expand our reach to others not sitting in our clinics who have the same rare condition or are at risk.”
After cascade testing, Dr. Garcia said, she invites family members with positive results to have baseline CT scans and pulmonary function testing. “And if there’s anything abnormal, we’re inviting them to have regular follow-up testing,” she said, “because we advise starting antifibrotic treatment at the very first sign of disease worsening.”
Such an approach to genetic testing for patients and relatives is described in a statement commissioned by the Pulmonary Fibrosis Foundation and published last year in the journal Chest (2022:162[2]:394-405). The statement, for which Dr. Newton and Dr. Garcia were among the authors, also lists clinical features within patients and families suggestive of a possible genetic pathway, and describes the potential yield for identifying a variant in different clinical scenarios.
Pathogenic variants in telomere genes as well as findings of short telomere length are associated with various extrapulmonary manifestations such as liver dysfunction, bone marrow dysfunction, and head and neck cancers, Dr. Newton said, making surveillance and referrals important. (Rare variants and short telomere length are associated with disease progression across several non-IPF diagnoses as well.)
Moreover, short telomeres may signal the need to avoid long-term immunosuppression. Research published in 2019 from multiple cohorts, and led by Dr. Newton and Dr. Garcia, showed that short telomere length is associated with worse outcomes (faster time to composite death, transplant, FVC decline, and hospitalization) in patients with IPF who received immunosuppression. These adverse outcomes were not found in IPF patients with normal telomere lengths who received similar immunosuppression (Am J Respir Crit Care Med. 2019;200(3):336-347).
Gene sequencing and telomere length measurement are described in the 2020 Chest statement on the role of genetic testing in PF as yielding “different yet complementary information.” Short age-adjusted telomere length (less than the 10th percentile) is common in those with pathogenic variants in telomere genes, but it can also occur in the absence of identifiable rare telomere-related variants, the statement says. Telomere length testing can be helpful, it notes, in determining the significance of a “variant of unknown significance (VUS)” if gene sequencing identifies one.