Capitalizing on the heterogeneous effects of CFTR nonsense and frameshift variants to inform therapeutic strategy for cystic fibrosis.

CFTR modulators have revolutionized the treatment of individuals with cystic fibrosis (CF) by improving the function of existing protein. Unfortunately, almost half of the disease-causing variants in CFTR are predicted to introduce premature termination codons (PTC) thereby causing absence of full-length CFTR protein. We hypothesized that a subset of nonsense and frameshift variants in CFTR allow expression of truncated protein that might respond to FDA-approved CFTR modulators. To address this concept, we selected 26 PTC-generating variants from four regions of CFTR and determined their consequences on CFTR mRNA, protein and function using intron-containing minigenes expressed in 3 cell lines (HEK293, MDCK and CFBE41o-) and patient-derived conditionally reprogrammed primary nasal epithelial cells. The PTC-generating variants fell into five groups based on RNA and protein effects. Group A (reduced mRNA, immature (core glycosylated) protein, function <1% (n = 5)) and Group B (normal mRNA, immature protein, function <1% (n = 10)) variants were unresponsive to modulator treatment. However, Group C (normal mRNA, mature (fully glycosylated) protein, function >1% (n = 5)), Group D (reduced mRNA, mature protein, function >1% (n = 5)) and Group E (aberrant RNA splicing, mature protein, function > 1% (n = 1)) variants responded to modulators. Increasing mRNA level by inhibition of NMD led to a significant amplification of modulator effect upon a Group D variant while response of a Group A variant was unaltered. Our work shows that PTC-generating variants should not be generalized as genetic 'nulls' as some may allow generation of protein that can be targeted to achieve clinical benefit.

Descriptions of the Pain Experience in Adults and Adolescents with Cystic Fibrosis.

BACKGROUND: People living with cystic fibrosis experience pain that is associated with decreased quality of life, poorer health outcomes, and increased mortality. Though pain is highly prevalent as a symptom, it is currently unknown how persons with CF describe their pain experiences or the ways those experiences impact their lives. AIMS: To explore and describe ways adolescents and adults with CF experience pain. Design/Setting/Subjects/Methods: An exploratory descriptive design was implemented to perform interviews with 10 individuals with CF and self-reported moderate to severe pain. The interviews explored their pain experiences within five domains: Pain Characteristics, Activities, Relationships, Work/School Life, and Health Care Team. Transcribed interviews underwent a content analysis with team-based constant comparisons. RESULTS: Individuals with CF identify the disease as being painful; express how pain negatively affects all aspects of their lives, including loss of functionality and productivity; and are able to disclose their pain to those with whom they have relationships. Adolescents feel an emotional toll from the loss of socialization as a result of pain and feel their health care team adequately supports their pain. Adults express a unique emotional pain component to CF and feel stigmatized and unsupported by their health care team when asking for pain management solutions. CONCLUSION: There are differences in how pain is perceived by adolescents and adults with CF that have otherwise not been reported in the current literature. Further explorations of pain across the lifespan and health care provider attitudes toward pain management are needed to guide the development of effective pain management interventions for those with CF.

A survey of cystic fibrosis physicians' views on lung transplant referral in the era of elexacaftor/tezacaftor/ivacaftor.

RATIONALE: In 2015, a survey of cystic fibrosis (CF) physicians showed significant gaps in lung transplant (LTx) referral knowledge. Subsequently, LTx referral guidelines for people with CF were published, and elexacaftor/tezacaftor/ivacaftor (ETI) became available for >80% of people in the United States (US). We sought to assess physicians' LTx referral knowledge and self-reported referral practices. METHODS: CF center directors in the US were surveyed about LTx. Questions addressed transplant referral indications, contraindications, testing, and the impact of ETI on referral timing. Thematic analysis was used to assess responses to open-ended questions. RESULTS: There were 110/309 (36%) responses. Respondents identified several referral indications, including rapid decline in FEV1 (93%), recurrent hemoptysis (80%), hypoxemia (79%), and pulmonary hypertension (75%). Over 70% of respondents reported using oximetry, echocardiogram, and blood gas to assess disease severity. Respondents were more likely to find early LTx discussions useful for patients not on modulators versus on modulators (87% vs. 63%, p < .005). Most respondents (66%) reported delaying LTx referral for some patients with FEV1 30%-40% who met criteria, while 26% had delayed referral for patients with FEV1 < 30%. Uncertainty regarding optimal LTx referral timing for patients on ETI was a prominent theme of the qualitative analysis. CONCLUSIONS: While physician knowledge about LTx referral indications appears improved since the CF referral guidelines were published, uncertainty about referral timing is pervasive, and the guidelines will need to be updated as more data become available about the long-term effectiveness of ETI in advanced lung disease.

Sweat test for cystic fibrosis: Wearable sweat sensor vs. standard laboratory test.

BACKGROUND: Sweat chloride testing for diagnosis of cystic fibrosis (CF) involves sweat induction, collection and handling, and measurement in an analytical lab. We have developed a wearable sensor with an integrated salt bridge for real-time measurement of sweat chloride concentration. Here, in a proof-of-concept study, we compare the performance of the sensor to current clinical practice in CF patients and healthy subjects. METHOD: Sweat was induced on both forearms of 10 individuals with CF and 10 healthy subjects using pilocarpine iontophoresis. A Macroduct sweat collection device was attached to one arm and sweat was collected for 30 min and then sent for laboratory analysis. A sensor was attached to the other arm and the chloride ion concentration monitored in real time for 30 min using a Bluetooth transceiver and smart phone app. RESULTS: Stable sweat chloride measurements were obtained within 15 min following sweat induction using the wearable sensor. We define the detection time as the time at which the standard deviation of the real-time chloride ion concentration remained below 2 mEq/L for 5 min. The sweat volume for sensor measurements at the detection time was 13.1 ±â€¯11.4 µL (SD), in many cases lower than the minimum sweat volume of 15 µL for conventional testing. The mean difference between sweat chloride concentrations measured by the sensor and the conventional laboratory practice was 6.2 ±â€¯9.5 mEq/L (SD), close to the arm-to-arm variation of about 3 mEq/L. The Pearson correlation coefficient between the two measurements was 0.97 highlighting the excellent agreement between the two methods. CONCLUSION: A wearable sensor can be used to make real-time measurements of sweat chloride within 15 min following sweat induction, requiring a small sweat volume, and with excellent agreement to standard methods.

Microstructural alterations of sputum in cystic fibrosis lung disease.

The stasis of mucus secretions in the lungs of cystic fibrosis (CF) patients leads to recurrent infections and pulmonary exacerbations, resulting in decreased survival. Prior studies have assessed the biochemical and biophysical features of airway mucus in individuals with CF. However, these measurements are unable to probe mucus structure on microscopic length scales relevant to key players in the progression of CF-related lung disease, namely, viruses, bacteria, and neutrophils. In this study, we quantitatively determined sputum microstructure based on the diffusion of muco-inert nanoparticle probes in CF sputum and found that a reduction in sputum mesh pore size is characteristic of CF patients with reduced lung function, as indicated by measured FEV1. We also discovered that the effect of ex vivo treatment of CF sputum with rhDNase I (Pulmozyme) on microstructure is dependent upon the time interval between the most recent inhaled rhDNase I treatment and the sample collection. Microstructure of mucus may serve as a marker for the extent of CF lung disease and as a parameter for assessing the effectiveness of mucus-altering agents.