Genetic Modifying Factors of Cystic Fibrosis Phenotype: A Challenge for Modern Medicine

The solute carrier family 26 member 9 modifies rapidly progressing cystic fibrosis associated with homozygous F508del CFTR mutation

BACKGROUND AND AIMS

Cystic fibrosis (CF) is an autosomal recessive disease caused by mutations to the CF transmembrane conductance regulator (CFTR). Symptoms and severity of the disease can be quite variable suggesting modifier genes play an important role.

MATERIALS AND METHODS

Exome sequencing was performed on six individuals carrying homozygous deltaF508 for CFTR genotype but present with rapidly progressing CF (RPCF). Data was analyzed using an unbiased genome-wide genetic burden test against 3076 controls. Single cell RNA sequencing data from LungMAP was utilized to evaluate unique and co-expression of candidate genes, and structural modeling to evaluate the deleterious effects of identified candidate variants.

RESULTS

We have identified solute carrier family 26 member 9 (SLC26A9) as a modifier gene to be associated with RPCF. Two rare missense SLC26A9 variants were discovered in three of six individuals deemed to have RPCF: c.229G > A; p.G77S (present in two patients), and c.1885C > T; p.P629S. Co-expression of SLC26A9 and CFTR mRNA is limited across different lung cell types, with the highest level of co-expression seen in human (6.3 %) and mouse (9.0 %) alveolar type 2 (AT2) cells. Structural modeling suggests deleterious effects of these mutations as they are in critical protein domains which might affect the anion transport capability of SLC26A9.

CONCLUSION

The enrichment of rare and potentially deleterious SLC26A9 mutations in patients with RPCF suggests SLC26A9 may act as an alternative anion transporter in CF and is a modifier gene associated with this lung phenotype.

Diagnosis and Management of Simple and Complicated Meconium Ileus in Cystic Fibrosis, a Systematic Review

The early management of neonates with meconium ileus (MI) and cystic fibrosis (CF) is highly variable across countries and is not standardized. We conducted a systematic review according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses statement. The protocol was registered in PROSPERO (CRD42024522838). Studies from three providers of academic search engines were checked for inclusion criteria, using the following search terms: meconium ileus AND cystic fibrosis OR mucoviscidosis. Regarding the patient population studied, the inclusion criteria were defined using our predefined PICOT framework: studies on neonates with simple or complicated meconium which were confirmed to have cystic fibrosis and were conservatively managed or surgically treated. Results: A total of 566 publications from the last 10 years were verified by the authors of this review to find the most recent and relevant data, and only 8 met the inclusion criteria. Prenatally diagnosed meconium pseudocysts, bowel dilation, and ascites on ultrasound are predictors of neonatal surgery and risk factor for negative 12-month clinical outcomes in MI-CF newborns. For simple MI, conservative treatment with hypertonic solutions enemas can be effective in more than 25% of cases. If repeated enemas fail to disimpact the bowels, the Bishop-Koop stoma is a safe option. No comprehensive research has been conducted so far to determine the ideal surgical protocol for complicated MI. We only found three studies that reported the types of stomas performed and another study comparing the outcomes of patients depending on the surgical management; the conclusions are contradictory especially since the number of cases analyzed in each study was small. Between 18% and 38% of patients with complicated MI will require reoperation for various complications and the mortality rate varies between 0% and 8%. Conclusion: This study reveals a lack of strong data to support management decisions, unequivocally shows that the care of infants with MI is not standardized, and suggests a great need for international collaborative studies.

Update on advances in cystic fibrosis towards a cure and implications for primary care clinicians

During the past quarter century, the diagnosis and treatment of cystic fibrosis (CF) have been transformed by molecular sciences that initiated a new era with discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. The knowledge gained from that breakthrough has had dramatic clinical impact. Although once a diagnostic dilemma with long delays, preventable deaths, and irreversible pathology, CF can now be routinely diagnosed shortly after birth through newborn screening programs. This strategy of pre-symptomatic identification has eliminated the common diagnostic "odyssey" that was a failure of the healthcare delivery system causing psychologically traumatic experiences for parents. Therapeutic advances of many kinds have culminated in CFTR modulator treatment that can reduce the effects of or even correct the molecular defect in the chloride channel -the basic cause of CF. This astonishing advance has transformed CF care as described fully herein. Despite this impressive progress, there are challenges and controversies in the delivery of care. Issues include how best to achieve high sensitivity newborn screening with acceptable specificity; what course of action is appropriate for children who are identified through the unavoidable incidental findings of screening tests (CFSPID/CRMS cases and heterozygote carriers); how best to ensure genetic counseling; when to initiate the very expensive but life-saving CFTR modulator drugs; how to identify new CFTR modulator drugs for patients with non-responsive CFTR variants; how to adjust other therapeutic modalities; and how to best partner with primary care clinicians. Progress always brings new challenges, and this has been evident worldwide for CF. Consequently, this article summarizes the major advances of recent years along with controversies and describes their implications with an international perspective.

Widespread alterations in systemic immune profile are linked to lung function heterogeneity and airway microbes in cystic fibrosis

BACKGROUND

Excessive inflammation and recurrent airway infections characterize people with cystic fibrosis (pwCF), a disease with highly heterogeneous clinical outcomes. How the overall immune response is affected in pwCF, its relationships with the lung microbiome, and the source of clinical heterogeneity have not been fully elucidated.

METHODS

Peripheral blood and sputum samples were collected from 28 pwCF and an age-matched control group. Systemic immune cell subsets and surface markers were quantified using multiparameter flow cytometry. Lung microbiome composition was reconstructed using metatranscriptomics on sputum samples, and microbial taxa were correlated to circulating immune cells and surface markers expression.

RESULTS

In pwCF, we found a specific systemic immune profile characterized by widespread hyperactivation and altered frequencies of several subsets. These included substantial changes in B-cell subsets, enrichment of CD35+/CD49d+ neutrophils, and reduction in dendritic cells. Activation markers and checkpoint molecule expression levels differed from healthy subjects. CTLA-4 expression was increased in Tregs and, together with impaired B-cell subsets, correlated with patients' lung function. Concentrations and frequencies of key immune cells and marker expression correlated with the relative abundance of commensal and pathogenic bacteria in the lungs.

CONCLUSION

The CF-specific immune signature, involving hyperactivation, immune dysregulation with alteration in Treg homeostasis, and impaired B-cell function, is a potential source of lung function heterogeneity. The activity of specific microbes contributes to disrupting the balance of the immune response. Our data provide a unique foundation for identifying novel markers and immunomodulatory targets to develop the future of cystic fibrosis treatment and management.

Constitutional chromosomal anomalies in children, fetal alcohol syndrome, and maternal toxicant exposures: A longitudinal cohort study

DNA alterations in gametes, which may occur either spontaneously or as a result of exposure to genotoxicants, can lead to constitutional chromosomal anomalies in the offspring. Alcohol is an established genotoxicant. The goal of this hypothesis-testing longitudinal cohort study was to evaluate the effect of significant/sustained maternal alcohol exposure on clinically diagnosed constitutional chromosomal anomalies among children diagnosed with fetal alcohol syndrome (FAS). De-identified eligibility and claim healthcare records, prospectively generated from the 1990-2012 Florida Medicaid system within the Independent Healthcare Research Database (IHRD), were analyzed. Children examined were continuously eligible with ≥ 8 outpatient office visits during the 96-month period following birth. Among these children, 377 were diagnosed with FAS and 137,135 were not. The incidence rate of chromosomal anomalies involving segregation (trisomy 13, 18, or 21, n = 625), microdeletions (microdeletion syndromes, n = 39), and point mutations (sickle-cell anemia/cystic fibrosis, n = 2570) were examined using frequency risk ratio (RR) and logistic regression (adjusted odds ratio (aOR) for sex, race, residence, socioeconomic/environmental exposure status, and birth date) models. The incidence rates of chromosomal anomalies involving segregation (RR=5.92, aOR=5.85) and microdeletions (RR=41.6, aOR=34.1) were significantly increased in the FAS cohort as compared to the non-diagnosed cohort, but there was no difference in the incidence rate of point mutations (RR=1.14, aOR=1.29). Maternal toxicant exposure should be considered in the etiology of constitutional chromosomal anomaly in offspring.

Lung Inflammatory Genes in Cystic Fibrosis and Their Relevance to Cystic Fibrosis Transmembrane Conductance Regulator Modulator Therapies

Cystic fibrosis (CF) is a monogenic syndrome determined by over 2000 mutations in the CF Transmembrane Conductance Regulator (CFTR) gene harbored on chromosome 7. In people with CF (PWCF), lung disease is the major determinant of morbidity and mortality and is characterized by a clinical phenotype which differs in the presence of equal mutational assets, indicating that genetic and environmental modifiers play an important role in this variability. Airway inflammation determines the pathophysiology of CF lung disease (CFLD) both at its onset and progression. In this narrative review, we aim to depict the inflammatory process in CF lung, with a particular emphasis on those genetic polymorphisms that could modify the clinical outcome of the respiratory disease in PWCF. The natural history of CF has been changed since the introduction of CFTR modulator therapies in the clinical arena. However, also in this case, there is a patient-to-patient variable response. We provide an overview on inflammatory/immunity gene variants that affect CFLD severity and an appraisal of the effects of CFTR modulator therapies on the inflammatory process in lung disease and how this knowledge may advance the optimization of the management of PWCF.

Tissue-Specific Regulation of CFTR Gene Expression

More than 2000 variations are described within the CFTR (Cystic Fibrosis Transmembrane Regulator) gene and related to large clinical issues from cystic fibrosis to mono-organ diseases. Although these CFTR-associated diseases have been well documented, a large phenotype spectrum is observed and correlations between phenotypes and genotypes are still not well established. To address this issue, we present several regulatory elements that can modulate CFTR gene expression in a tissue-specific manner. Among them, cis-regulatory elements act through chromatin loopings and take part in three-dimensional structured organization. With tissue-specific transcription factors, they form chromatin modules and can regulate gene expression. Alterations of specific regulations can impact and modulate disease expressions. Understanding all those mechanisms highlights the need to expand research outside the gene to enhance our knowledge.

The effect of Dnaaf5 gene dosage on primary ciliary dyskinesia phenotypes

DNAAF5 is a dynein motor assembly factor associated with the autosomal heterogenic recessive condition of motile cilia, primary ciliary dyskinesia (PCD). The effects of allele heterozygosity on motile cilia function are unknown. We used CRISPR-Cas9 genome editing in mice to recreate a human missense variant identified in patients with mild PCD and a second, frameshift-null deletion in Dnaaf5. Litters with Dnaaf5 heteroallelic variants showed distinct missense and null gene dosage effects. Homozygosity for the null Dnaaf5 alleles was embryonic lethal. Compound heterozygous animals with the missense and null alleles showed severe disease manifesting as hydrocephalus and early lethality. However, animals homozygous for the missense mutation had improved survival, with partially preserved cilia function and motor assembly observed by ultrastructure analysis. Notably, the same variant alleles exhibited divergent cilia function across different multiciliated tissues. Proteomic analysis of isolated airway cilia from mutant mice revealed reduction in some axonemal regulatory and structural proteins not previously reported in DNAAF5 variants. Transcriptional analysis of mouse and human mutant cells showed increased expression of genes coding for axonemal proteins. These findings suggest allele-specific and tissue-specific molecular requirements for cilia motor assembly that may affect disease phenotypes and clinical trajectory in motile ciliopathies.

Catching Cancer Early: The Importance of Dermato-Oncology Screening

The European Society for Medical Oncology experts have identified the main components of the long-term management of oncological patients. These include early diagnosis through population screening and periodic control of already diagnosed patients to identify relapses, recurrences, and other associated neoplasms. There are no generally accepted international guidelines for the long-term monitoring of patients with skin neoplasms (nonmelanoma skin cancer, malignant melanoma, precancerous-high-risk skin lesions). Still, depending on the experience of the attending physician and based on the data from the literature, one can establish monitoring intervals to supervise these high-risk population groups, educate the patient and monitor the general population.

Identification of Single Nucleotide Variants in SLC26A9 Gene in Patients with Cystic Fibrosis (p.Phe508del Homozygous) and its Association to Orkambi® (Lumacaftor and Ivacaftor) Response in vitro

BACKGROUND

Since patients with cystic fibrosis with different Cystic Fibrosis Transmembrane Regulator (CFTR) genotypes present a wide response variability for modulator drugs such as Orkambi®, it is important to screen variants in candidate genes with an impact on precision and personalized medicine, such as Solute Carrier Family 26, member 9 (SLC26A9) gene.

METHODS

Sanger sequencing for the exons and intron-exon boundary junctions of the SLC26A9 gene was employed in nine individuals with p.Phe508del homozygous genotype for the CFTR gene who were not under CFTR modulators therapy. The sequencing variants were evaluated by in silico prediction tools. The CFTR function was measured by cAMP-stimulated current (ΔIsc-eq-FSK) in polarized CFTR of human nasal epithelial cells cultured in micro-Ussing chambers with Orkambi®.

RESULTS

We found 24 intronic variants, three in the coding region (missense variants - rs74146719 and rs16856462 and synonymous - rs33943971), and three in the three prime untranslated region (3' UTR) region in the SLC26A9 gene. Twenty variants were considered benign according to American College of Medical Genetics and Genomics guidelines, and ten were classified as uncertain significance. Although some variants had deleterious predictions or possible alterations in splicing, the majority of predictions were benign or neutral. When we analyzed the ΔIsc-eq-FSK response to Orkambi®, there were no significant differences within the genotypes and alleles for all 30 variants in the SLC26A9 gene.

CONCLUSIONS

Among the nine individuals with p.Phe508del homozygous genotype for the CFTR gene, no pathogenic SLC26A9 variants were found, and we did not detect associations from the 30 SLC26A9 variants and the response to the Orkambi® in vitro.

Genetically transitional disease: a new concept in genomic medicine

Traditional classification of genetic diseases as monogenic and polygenic has lagged far behind scientific progress. In this opinion article, we propose and define a new terminology, genetically transitional disease (GTD), referring to cases where a large-effect mutation is necessary, but not sufficient, to cause disease. This leads to a working disease nosology based on gradients of four types of genetic architecture: monogenic, polygenic, GTD, and mixed. We present four scenarios under which GTD may occur; namely, subsets of traditionally Mendelian disease, modifiable Tier 1 monogenic conditions, variable penetrance, and situations where a genetic mutational spectrum produces qualitatively divergent pathologies. The implications of the new nosology in precision medicine are discussed, in which therapeutic options may target the molecular cause or the disease phenotype.

The effect of Dnaaf5 gene dosage on primary ciliary dyskinesia phenotypes

DNAAF5 is a dynein motor assembly factor associated with the autosomal heterogenic recessive condition of motile cilia, primary ciliary dyskinesia (PCD). The effects of allele heterozygosity on motile cilia function are unknown. We used CRISPR-Cas9 genome editing in mice to recreate a human missense variant identified in patients with mild PCD and a second, frameshift null deletion in Dnaaf5 . Litters with Dnaaf5 heteroallelic variants showed distinct missense and null gene dosage effects. Homozygosity for the null Dnaaf5 alleles was embryonic lethal. Compound heterozygous animals with the missense and null alleles showed severe disease manifesting as hydrocephalus and early lethality. However, animals homozygous for the missense mutation had improved survival, with partial preserved cilia function and motor assembly observed by ultrastructure analysis. Notably, the same variant alleles exhibited divergent cilia function across different multiciliated tissues. Proteomic analysis of isolated airway cilia from mutant mice revealed reduction in some axonemal regulatory and structural proteins not previously reported in DNAAF5 variants. While transcriptional analysis of mouse and human mutant cells showed increased expression of genes coding for axonemal proteins. Together, these findings suggest allele-specific and tissue-specific molecular requirements for cilia motor assembly that may affect disease phenotypes and clinical trajectory in motile ciliopathies.

Brief Summary

A mouse model of human DNAAF5 primary ciliary dyskinesia variants reveals gene dosage effects of mutant alleles and tissue-specific molecular requirements for cilia motor assembly.

Can Bioactive Food Substances Contribute to Cystic Fibrosis-Related Cardiovascular Disease Prevention?

Advances in cystic fibrosis (CF) care have significantly improved the quality of life and life expectancy of patients. Nutritional therapy based on a high-calorie, high-fat diet, antibiotics, as well as new therapies focused on CFTR modulators change the natural course of the disease. They do so by improving pulmonary function and growing BMI. However, the increased weight of such patients can lead to unwanted long-term cardiovascular effects. People with CF (pwCF) experience several cardiovascular risk factors. Such factors include a high-fat diet and increased dietary intake, altered lipid metabolism, a decrease in the level of fat-soluble antioxidants, heightened systemic inflammation, therapeutic interventions, and diabetes mellitus. PwCF must pay special attention to food and eating habits in order to maintain a nutritional status that is as close as possible to the proper physiological one. They also have to benefit from appropriate nutritional counseling, which is essential in the evolution and prognosis of the disease. Growing evidence collected in the last years shows that many bioactive food components, such as phytochemicals, polyunsaturated fatty acids, and antioxidants have favorable effects in the management of CF. An important positive effect is cardiovascular prevention. The possibility of preventing/reducing cardiovascular risk in CF patients enhances both quality of life and life expectancy in the long run.

Modifier Factors of Cystic Fibrosis Phenotypes: A Focus on Modifier Genes

Although cystic fibrosis (CF) is recognized as a monogenic disease, due to variants within the CFTR (Cystic Fibrosis Transmembrane Regulator) gene, an extreme clinical heterogeneity is described among people with CF (pwCF). Apart from the exocrine pancreatic status, most studies agree that there is little association between CFTR variants and disease phenotypes. Environmental factors have been shown to contribute to this heterogeneity, accounting for almost 50% of the variability of the lung function of pwCF. Nevertheless, pwCF with similar CFTR variants and sharing the same environment (such as in siblings) may have highly variable clinical manifestations not explained by CFTR variants, and only partly explained by environmental factors. It is recognized that genetic variants located outside the CFTR locus, named "modifier genes", influence the clinical expression of the disease. This short review discusses the latest studies that have described modifier factors associated with the various CF phenotypes as well as the response to the recent CFTR modulator therapies.

Nutritional and metabolic management for cystic fibrosis in a post-cystic fibrosis transmembrane conductance modulator era

PURPOSE OF REVIEW

The introduction of highly effective cystic fibrosis transmembrane conductance regulator modulators has resulted in a paradigm shift towards treating underlying cause of cystic fibrosis (CF) rather than the ensuing complications. In this review, we will describe the impact of these small molecules on growth, nutrition, and metabolic status in people with CF (pwCF).

RECENT FINDING

Results of clinical trials and real world data demonstrate that these small molecules are having a significant impact of on augmenting body weight, improving nutritional status and reducing gastrointestinal symptom burden. Early treatment can also positively impact on pancreatic endocrine and exocrine function.

SUMMARY

Nutritional and metabolic management of pwCF needs to change in order to maximize long term health and avoid future complications relating to obesity and increased cardiovascular risk. Longitudinal registry studies will be key to improve our understanding of the longer-term outcome of these new therapies.

Expanding ACMG variant classification guidelines into a general framework

BACKGROUND

The American College of Medical Genetics and Genomics (ACMG)-recommended five variant classification categories (pathogenic, likely pathogenic, uncertain significance, likely benign, and benign) have been widely used in medical genetics. However, these guidelines are fundamentally constrained in practice owing to their focus upon Mendelian disease genes and their dichotomous classification of variants as being either causal or not. Herein, we attempt to expand the ACMG guidelines into a general variant classification framework that takes into account not only the continuum of clinical phenotypes, but also the continuum of the variants' genetic effects, and the different pathological roles of the implicated genes.

MAIN BODY

As a disease model, we employed chronic pancreatitis (CP), which manifests clinically as a spectrum from monogenic to multifactorial. Bearing in mind that any general conceptual proposal should be based upon sound data, we focused our analysis on the four most extensively studied CP genes, PRSS1, CFTR, SPINK1 and CTRC. Based upon several cross-gene and cross-variant comparisons, we first assigned the different genes to two distinct categories in terms of disease causation: CP-causing (PRSS1 and SPINK1) and CP-predisposing (CFTR and CTRC). We then employed two new classificatory categories, "predisposing" and "likely predisposing", to replace ACMG's "pathogenic" and "likely pathogenic" categories in the context of CP-predisposing genes, thereby classifying all pathologically relevant variants in these genes as "predisposing". In the case of CP-causing genes, the two new classificatory categories served to extend the five ACMG categories whilst two thresholds (allele frequency and functional) were introduced to discriminate "pathogenic" from "predisposing" variants.

CONCLUSION

Employing CP as a disease model, we expand ACMG guidelines into a five-category classification system (predisposing, likely predisposing, uncertain significance, likely benign, and benign) and a seven-category classification system (pathogenic, likely pathogenic, predisposing, likely predisposing, uncertain significance, likely benign, and benign) in the context of disease-predisposing and disease-causing genes, respectively. Taken together, the two systems constitute a general variant classification framework that, in principle, should span the entire spectrum of variants in any disease-related gene. The maximal compliance of our five-category and seven-category classification systems with the ACMG guidelines ought to facilitate their practical application.

Current Advances in RNA Therapeutics for Human Diseases

Following the discovery of nucleic acids by Friedrich Miescher in 1868, DNA and RNA were recognized as the genetic code containing the necessary information for proper cell functioning. In the years following these discoveries, vast knowledge of the seemingly endless roles of RNA have become better understood. Additionally, many new types of RNAs were discovered that seemed to have no coding properties (non-coding RNAs), such as microRNAs (miRNAs). The discovery of these new RNAs created a new avenue for treating various human diseases. However, RNA is relatively unstable and is degraded fairly rapidly once administered; this has led to the development of novel delivery mechanisms, such as nanoparticles to increase stability as well as to prevent off-target effects of these molecules. Current advances in RNA-based therapies have substantial promise in treating and preventing many human diseases and disorders through fixing the pathology instead of merely treating the symptomology similarly to traditional therapeutics. Although many RNA therapeutics have made it to clinical trials, only a few have been FDA approved thus far. Additionally, the results of clinical trials for RNA therapeutics have been ambivalent to date, with some studies demonstrating potent efficacy, whereas others have limited effectiveness and/or toxicity. Momentum is building in the clinic for RNA therapeutics; future clinical care of human diseases will likely comprise promising RNA therapeutics. This review focuses on the current advances of RNA therapeutics and addresses current challenges with their development.