Genetic modifiers of body mass index in individuals with cystic fibrosis.

To identify modifier loci underlying variation in body mass index (BMI) in persons with cystic fibrosis (pwCF), we performed a genome-wide association study (GWAS). Utilizing longitudinal height and weight data, along with demographic information and covariates from 4,393 pwCF, we calculated AvgBMIz representing the average of per-quarter BMI Z scores. The GWAS incorporated 9.8M single nucleotide polymorphisms (SNPs) with a minor allele frequency (MAF) > 0.005 extracted from whole-genome sequencing (WGS) of each study subject. We observed genome-wide significant association with a variant in FTO (FaT mass and Obesity-associated gene; rs28567725; p value = 1.21e-08; MAF = 0.41, ß = 0.106; n = 4,393 individuals) and a variant within ADAMTS5 (A Disintegrin And Metalloproteinase with ThromboSpondin motifs 5; rs162500; p value = 2.11e-10; MAF = 0.005, ß = -0.768; n = 4,085 pancreatic-insufficient individuals). Notably, BMI-associated variants in ADAMTS5 occur on a haplotype that is much more common in African (AFR, MAF = 0.183) than European (EUR, MAF = 0.006) populations (1000 Genomes project). A polygenic risk score (PRS) calculated using 924 SNPs (excluding 17 in FTO) showed significant association with AvgBMIz (p value = 2.2e-16; r2 = 0.03). Association between variants in FTO and the PRS correlation reveals similarities in the genetic architecture of BMI in CF and the general population. Inclusion of Black individuals in whom the single-gene disorder CF is much less common but genomic diversity is greater facilitated detection of association with variants that are in LD with functional SNPs in ADAMTS5. Our results illustrate the importance of population diversity, particularly when attempting to identify variants that manifest only under certain physiologic conditions.

MagicalRsq-X: A cross-cohort transferable genotype imputation quality metric.

Since genotype imputation was introduced, researchers have been relying on the estimated imputation quality from imputation software to perform post-imputation quality control (QC). However, this quality estimate (denoted as Rsq) performs less well for lower-frequency variants. We recently published MagicalRsq, a machine-learning-based imputation quality calibration, which leverages additional typed markers from the same cohort and outperforms Rsq as a QC metric. In this work, we extended the original MagicalRsq to allow cross-cohort model training and named the new model MagicalRsq-X. We removed the cohort-specific estimated minor allele frequency and included linkage disequilibrium scores and recombination rates as additional features. Leveraging whole-genome sequencing data from TOPMed, specifically participants in the BioMe, JHS, WHI, and MESA studies, we performed comprehensive cross-cohort evaluations for predominantly European and African ancestral individuals based on their inferred global ancestry with the 1000 Genomes and Human Genome Diversity Project data as reference. Our results suggest MagicalRsq-X outperforms Rsq in almost every setting, with 7.3%-14.4% improvement in squared Pearson correlation with true R2, corresponding to 85-218 K variant gains. We further developed a metric to quantify the genetic distances of a target cohort relative to a reference cohort and showed that such metric largely explained the performance of MagicalRsq-X models. Finally, we found MagicalRsq-X saved up to 53 known genome-wide significant variants in one of the largest blood cell trait GWASs that would be missed using the original Rsq for QC. In conclusion, MagicalRsq-X shows superiority for post-imputation QC and benefits genetic studies by distinguishing well and poorly imputed lower-frequency variants.

Pleiotropic modifiers of age-related diabetes and neonatal intestinal obstruction in cystic fibrosis.

Individuals with cystic fibrosis (CF) develop complications of the gastrointestinal tract influenced by genetic variants outside of CFTR. Cystic fibrosis-related diabetes (CFRD) is a distinct form of diabetes with a variable age of onset that occurs frequently in individuals with CF, while meconium ileus (MI) is a severe neonatal intestinal obstruction affecting ∼20% of newborns with CF. CFRD and MI are slightly correlated traits with previous evidence of overlap in their genetic architectures. To better understand the genetic commonality between CFRD and MI, we used whole-genome-sequencing data from the CF Genome Project to perform genome-wide association. These analyses revealed variants at 11 loci (6 not previously identified) that associated with MI and at 12 loci (5 not previously identified) that associated with CFRD. Of these, variants at SLC26A9, CEBPB, and PRSS1 associated with both traits; variants at SLC26A9 and CEBPB increased risk for both traits, while variants at PRSS1, the higher-risk alleles for CFRD, conferred lower risk for MI. Furthermore, common and rare variants within the SLC26A9 locus associated with MI only or CFRD only. As expected, different loci modify risk of CFRD and MI; however, a subset exhibit pleiotropic effects indicating etiologic and mechanistic overlap between these two otherwise distinct complications of CF.

MagicalRsq: Machine-learning-based genotype imputation quality calibration.

Whole-genome sequencing (WGS) is the gold standard for fully characterizing genetic variation but is still prohibitively expensive for large samples. To reduce costs, many studies sequence only a subset of individuals or genomic regions, and genotype imputation is used to infer genotypes for the remaining individuals or regions without sequencing data. However, not all variants can be well imputed, and the current state-of-the-art imputation quality metric, denoted as standard Rsq, is poorly calibrated for lower-frequency variants. Here, we propose MagicalRsq, a machine-learning-based method that integrates variant-level imputation and population genetics statistics, to provide a better calibrated imputation quality metric. Leveraging WGS data from the Cystic Fibrosis Genome Project (CFGP), and whole-exome sequence data from UK BioBank (UKB), we performed comprehensive experiments to evaluate the performance of MagicalRsq compared to standard Rsq for partially sequenced studies. We found that MagicalRsq aligns better with true R2 than standard Rsq in almost every situation evaluated, for both European and African ancestry samples. For example, when applying models trained from 1,992 CFGP sequenced samples to an independent 3,103 samples with no sequencing but TOPMed imputation from array genotypes, MagicalRsq, compared to standard Rsq, achieved net gains of 1.4 million rare, 117k low-frequency, and 18k common variants, where net gains were gained numbers of correctly distinguished variants by MagicalRsq over standard Rsq. MagicalRsq can serve as an improved post-imputation quality metric and will benefit downstream analysis by better distinguishing well-imputed variants from those poorly imputed. MagicalRsq is freely available on GitHub.

Genetic variation in severe cystic fibrosis liver disease is associated with novel mechanisms for disease pathogenesis.

BACKGROUND AND AIMS: It is not known why severe cystic fibrosis (CF) liver disease (CFLD) with portal hypertension occurs in only ~7% of people with CF. We aimed to identify genetic modifiers for severe CFLD to improve understanding of disease mechanisms. APPROACH AND RESULTS: Whole-genome sequencing was available in 4082 people with CF with pancreatic insufficiency (n = 516 with severe CFLD; n = 3566 without CFLD). We tested ~15.9 million single nucleotide polymorphisms (SNPs) for association with severe CFLD versus no-CFLD, using pre-modulator clinical phenotypes including (1) genetic variant ( SERPINA1 ; Z allele) previously associated with severe CFLD; (2) candidate SNPs (n = 205) associated with non-CF liver diseases; (3) genome-wide association study of common/rare SNPs; (4) transcriptome-wide association; and (5) gene-level and pathway analyses. The Z allele was significantly associated with severe CFLD ( p = 1.1 × 10 -4 ). No significant candidate SNPs were identified. A genome-wide association study identified genome-wide significant SNPs in 2 loci and 2 suggestive loci. These 4 loci contained genes [significant, PKD1 ( p = 8.05 × 10 -10 ) and FNBP1 ( p = 4.74 × 10 -9 ); suggestive, DUSP6 ( p = 1.51 × 10 -7 ) and ANKUB1 ( p = 4.69 × 10 -7 )] relevant to severe CFLD pathophysiology. The transcriptome-wide association identified 3 genes [ CXCR1 ( p = 1.01 × 10 -6 ) , AAMP ( p = 1.07 × 10 -6 ), and TRBV24 ( p = 1.23 × 10 -5 )] involved in hepatic inflammation and innate immunity. Gene-ranked analyses identified pathways enriched in genes linked to multiple liver pathologies. CONCLUSION: These results identify loci/genes associated with severe CFLD that point to disease mechanisms involving hepatic fibrosis, inflammation, innate immune function, vascular pathology, intracellular signaling, actin cytoskeleton and tight junction integrity and mechanisms of hepatic steatosis and insulin resistance. These discoveries will facilitate mechanistic studies and the development of therapeutics for severe CFLD.

Genetic Modifiers of Cystic Fibrosis Lung Disease Severity: Whole-Genome Analysis of 7,840 Patients.

Rationale: Lung disease is the major cause of morbidity and mortality in persons with cystic fibrosis (pwCF). Variability in CF lung disease has substantial non-CFTR (CF transmembrane conductance regulator) genetic influence. Identification of genetic modifiers has prognostic and therapeutic importance. Objectives: Identify genetic modifier loci and genes/pathways associated with pulmonary disease severity. Methods: Whole-genome sequencing data on 4,248 unique pwCF with pancreatic insufficiency and lung function measures were combined with imputed genotypes from an additional 3,592 patients with pancreatic insufficiency from the United States, Canada, and France. This report describes association of approximately 15.9 million SNPs using the quantitative Kulich normal residual mortality-adjusted (KNoRMA) lung disease phenotype in 7,840 pwCF using premodulator lung function data. Measurements and Main Results: Testing included common and rare SNPs, transcriptome-wide association, gene-level, and pathway analyses. Pathway analyses identified novel associations with genes that have key roles in organ development, and we hypothesize that these genes may relate to dysanapsis and/or variability in lung repair. Results confirmed and extended previous genome-wide association study findings. These whole-genome sequencing data provide finely mapped genetic information to support mechanistic studies. No novel primary associations with common single variants or rare variants were found. Multilocus effects at chr5p13 (SLC9A3/CEP72) and chr11p13 (EHF/APIP) were identified. Variant effect size estimates at associated loci were consistently ordered across the cohorts, indicating possible age or birth cohort effects. Conclusions: This premodulator genomic, transcriptomic, and pathway association study of 7,840 pwCF will facilitate mechanistic and postmodulator genetic studies and the development of novel therapeutics for CF lung disease.

Genetic association and transcriptome integration identify contributing genes and tissues at cystic fibrosis modifier loci.

Cystic Fibrosis (CF) exhibits morbidity in several organs, including progressive lung disease in all patients and intestinal obstruction at birth (meconium ileus) in ~15%. Individuals with the same causal CFTR mutations show variable disease presentation which is partly attributed to modifier genes. With >6,500 participants from the International CF Gene Modifier Consortium, genome-wide association investigation identified a new modifier locus for meconium ileus encompassing ATP12A on chromosome 13 (min p = 3.83x10(-10)); replicated loci encompassing SLC6A14 on chromosome X and SLC26A9 on chromosome 1, (min p<2.2x10(-16), 2.81x10(-11), respectively); and replicated a suggestive locus on chromosome 7 near PRSS1 (min p = 2.55x10(-7)). PRSS1 is exclusively expressed in the exocrine pancreas and was previously associated with non-CF pancreatitis with functional characterization demonstrating impact on PRSS1 gene expression. We thus asked whether the other meconium ileus modifier loci impact gene expression and in which organ. We developed and applied a colocalization framework called the Simple Sum (SS) that integrates regulatory and genetic association information, and also contrasts colocalization evidence across tissues or genes. The associated modifier loci colocalized with expression quantitative trait loci (eQTLs) for ATP12A (p = 3.35x10(-8)), SLC6A14 (p = 1.12x10(-10)) and SLC26A9 (p = 4.48x10(-5)) in the pancreas, even though meconium ileus manifests in the intestine. The meconium ileus susceptibility locus on chromosome X appeared shifted in location from a previously identified locus for CF lung disease severity. Using the SS we integrated the lung disease association locus with eQTLs from nasal epithelia of 63 CF participants and demonstrated evidence of colocalization with airway-specific regulation of SLC6A14 (p = 2.3x10(-4)). Cystic Fibrosis is realizing the promise of personalized medicine, and identification of the contributing organ and understanding of tissue specificity for a gene modifier is essential for the next phase of personalizing therapeutic strategies.

Sources of Variation in Sweat Chloride Measurements in Cystic Fibrosis.

RATIONALE: Expanding the use of cystic fibrosis transmembrane conductance regulator (CFTR) potentiators and correctors for the treatment of cystic fibrosis (CF) requires precise and accurate biomarkers. Sweat chloride concentration provides an in vivo assessment of CFTR function, but it is unknown the degree to which CFTR mutations account for sweat chloride variation. OBJECTIVES: To estimate potential sources of variation for sweat chloride measurements, including demographic factors, testing variability, recording biases, and CFTR genotype itself. METHODS: A total of 2,639 sweat chloride measurements were obtained in 1,761 twins/siblings from the CF Twin-Sibling Study, French CF Modifier Gene Study, and Canadian Consortium for Genetic Studies. Variance component estimation was performed by nested mixed modeling. MEASUREMENTS AND MAIN RESULTS: Across the tested CF population as a whole, CFTR gene mutations were found to be the primary determinant of sweat chloride variability (56.1% of variation) with contributions from variation over time (e.g., factors related to testing on different days; 13.8%), environmental factors (e.g., climate, family diet; 13.5%), other residual factors (e.g., test variability; 9.9%), and unique individual factors (e.g., modifier genes, unique exposures; 6.8%) (likelihood ratio test, P < 0.001). Twin analysis suggested that modifier genes did not play a significant role because the heritability estimate was negligible (H2 = 0; 95% confidence interval, 0.0-0.35). For an individual with CF, variation in sweat chloride was primarily caused by variation over time (58.1%) with the remainder attributable to residual/random factors (41.9%). CONCLUSIONS: Variation in the CFTR gene is the predominant cause of sweat chloride variation; most of the non-CFTR variation is caused by testing variability and unique environmental factors. If test precision and accuracy can be improved, sweat chloride measurement could be a valuable biomarker for assessing response to therapies directed at mutant CFTR.

Diabetes-related mortality in adults with cystic fibrosis. Role of genotype and sex.

RATIONALE: Diabetes is associated with increased mortality in cystic fibrosis. Aggressive screening and early institution of insulin treatment significantly reduced this risk over the period of 1992-2008. OBJECTIVES: To determine if progressive improvement in cystic fibrosis-related diabetes (CFRD) mortality has continued since 2008, and examine associations with CFTR genotypes linked to pancreatic insufficiency and to sex. METHODS: Chart review was performed on 664 patients followed from 2008 to 2012. MEASUREMENTS AND MAIN RESULTS: Overall mortality for patients with CFRD was 1.8 per 100 person-years, compared with 0.5 in patients with CF without diabetes (P = 0.0002); neither rate changed significantly from mortality reported for 2003-2008. Genotype impacted both mortality and diabetes risk: adults with severe CFTR genotypes experienced greater mortality at every age older than 32 years than those with mild genotypes (P = 0.002), and the risk of developing CFRD was also greatly increased in those with severe genotypes (prevalence 60% in adult patients with severe vs. 14% in adults with mild mutations). CFRD had a direct influence on mortality because it was associated with increased risk of death within each genotype category (20 vs. 2%, P = 0.007 for mild; 12 vs. 4%, P = 0.012 for severe). There was also a sex difference in adults with severe CFTR genotypes; both mortality and CFRD prevalence were higher at every age in females than males. CONCLUSIONS: Despite substantial improvement over time, mortality for CFRD patients greater than 30 years remains higher than for patients with CF without diabetes.

Variation in MSRA modifies risk of neonatal intestinal obstruction in cystic fibrosis.

Meconium ileus (MI), a life-threatening intestinal obstruction due to meconium with abnormal protein content, occurs in approximately 15 percent of neonates with cystic fibrosis (CF). Analysis of twins with CF demonstrates that MI is a highly heritable trait, indicating that genetic modifiers are largely responsible for this complication. Here, we performed regional family-based association analysis of a locus that had previously been linked to MI and found that SNP haplotypes 5' to and within the MSRA gene were associated with MI (P = 1.99 × 10(-5) to 1.08 × 10(-6); Bonferroni P = 0.057 to 3.1 × 10(-3)). The haplotype with the lowest P value showed association with MI in an independent sample of 1,335 unrelated CF patients (OR = 0.72, 95% CI [0.53-0.98], P = 0.04). Intestinal obstruction at the time of weaning was decreased in CF mice with Msra null alleles compared to those with wild-type Msra resulting in significant improvement in survival (P = 1.2 × 10(-4)). Similar levels of goblet cell hyperplasia were observed in the ilea of the Cftr(-/-) and Cftr(-/-)Msra(-/-) mice. Modulation of MSRA, an antioxidant shown to preserve the activity of enzymes, may influence proteolysis in the developing intestine of the CF fetus, thereby altering the incidence of obstruction in the newborn period. Identification of MSRA as a modifier of MI provides new insight into the biologic mechanism of neonatal intestinal obstruction caused by loss of CFTR function.

Cat and dog exposure and respiratory morbidities in cystic fibrosis.

OBJECTIVE: To understand the triggers that may impact respiratory health in cystic fibrosis (CF), including the effects of pets, because environmental factors contribute to one-half of the variation in lung function in patients with CF. STUDY DESIGN: A total of 703 subjects with CF were recruited through the US CF Twin-Sibling Study. Questionnaires were used to determine the presence/absence of cats and dogs in households with a child with CF. Questionnaires, chart review, and US CF Foundation Patient Registry data were used to track respiratory and infection outcomes. RESULTS: Within the sample, 47% of subjects reported owning a dog, and 28% reported owning a cat. After adjustment for demographic factors, dog ownership was not associated with any adverse clinical outcomes, and cat ownership was associated an increased risk in developing nasal polyps (aOR 1.66; P = .024) compared with noncat owners. Subjects who owned both cats and dogs were twice as likely to report wheezing compared with other subjects (aOR: 2.01; P = .009). There were no differences in prevalence and age of acquisition for the common CF respiratory pathogens Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus between cat/dog owners and noncat/dog owners. CONCLUSIONS: Cat ownership was associated with a greater frequency of developing nasal polyps and combined cat-dog ownership was associated with a greater rate of wheezing. Prospective studies are needed to confirm these associations and the potential psychosocial benefits of cat and/or dog ownership.

Insulin pump use in young children in the T1D Exchange clinic registry is associated with lower hemoglobin A1c levels than injection therapy.

Insulin delivery via injection and continuous subcutaneous insulin infusion (CSII) via insulin pump were compared in a cross-sectional study (n = 669) and retrospective longitudinal study (n = 1904) of young children (<6 yr) with type 1 diabetes (T1D) participating in the T1D Exchange clinic registry. Use of CSII correlated with longer T1D duration (p < 0.001), higher parental education (p < 0.001), and annual household income (p < 0.006) but not with race/ethnicity. Wide variation in pump use was observed among T1D Exchange centers even after adjusting for these factors, suggesting that prescriber preference is a substantial determinant of CSII use. Hemoglobin A1c (HbA1c) was lower in pump vs. injection users (7.9 vs. 8.5%, adjusted p < 0.001) in the cross-sectional study. In the longitudinal study, HbA1c decreased after initiation of CSII by 0.2%, on average (p < 0.001). Frequency of a severe hypoglycemia (SH) event did not differ in pump vs. injection users (p = 0.2). Frequency of ≥1 parent-reported diabetic ketoacidosis (DKA) event in the prior year was greater in pump users than injection users (10 vs. 8%, p = 0.04). No differences between pump and injection users were observed for clinic-reported DKA events. Children below 6 yr have many unique metabolic characteristics, feeding behaviors, and care needs compared with older children and adolescents. These data support the use of insulin pumps in this youngest age group, and suggest that metabolic control may be improved without increasing the frequency of SH, but care should be taken as to the possibly increased risk of DKA.

Self-reported exercise and longitudinal outcomes in cystic fibrosis: a retrospective cohort study.

BACKGROUND: Cystic fibrosis (CF) is characterized by recurrent respiratory infections and progressive lung disease. Whereas exercise may contribute to preserving lung function, its benefit is difficult to ascertain given the selection bias of healthier patients being more predisposed to exercise. Our objective was to examine the role of self-reported exercise with longitudinal lung function and body mass index (BMI) measures in CF. METHODS: A total of 1038 subjects with CF were recruited through the U.S. CF Twin-Sibling Study. Questionnaires were used to determine exercise habits. Questionnaires, chart review, and U.S. CF Foundation Patient Registry data were used to track outcomes. RESULTS: Within the study sample 75% of subjects self-reported regular exercise. Exercise was associated with an older age of diagnosis (p = 0.002), older age at the time of ascertainment (p < 0.001), and higher baseline FEV1 (p = 0.001), but not CFTR genotype (p = 0.64) or exocrine pancreatic function (p = 0.19). In adjusted mixed models, exercise was associated with both a reduced decline in FEV1 (p < 0.001) and BMI Z-score (p = 0.001) for adults, but not children aged 10-17 years old. CONCLUSIONS: In our retrospective study, self-reported exercise was associated with improved longitudinal nutritional and pulmonary outcomes in cystic fibrosis for adults. Although prospective studies are needed to confirm these associations, programs to promote regular exercise among individuals with cystic fibrosis would be beneficial.

The clinical utility of sequencing the entirety of CFTR.

BACKGROUND: Cystic fibrosis (CF) is caused by deleterious variants in each CFTR gene. We investigated the utility of whole-gene CFTR sequencing when fewer than two pathogenic or likely pathogenic (P/LP) variants were detected by conventional testing (sequencing of exons and flanking introns) of CFTR. METHODS: Individuals with features of CF and a CF-diagnostic sweat chloride concentration with zero or one P/LP variants identified by conventional testing enrolled in the CF Mutation Analysis Program (MAP) underwent whole-gene CFTR sequencing. Replication was performed on individuals enrolled in the CF Genome Project (CFGP), followed by phenotype review and interrogation of other genes. RESULTS: Whole-gene sequencing identified a second P/LP variant in 20/43 MAP enrollees (47 %) and 10/22 CFGP enrollees (45 %) who had one P/LP variant after conventional testing. No P/LP variants were detected when conventional testing was negative (MAP: n = 43; CFGP: n = 13). Genome-wide analysis was unable to find an alternative etiology in CFGP participants with fewer than two P/LP CFTR variants and CF could not be confirmed in 91 % following phenotype re-review. CONCLUSIONS: Whole-gene CFTR analysis is beneficial in individuals with one previously-identified P/LP variant and a CF-diagnostic sweat chloride. Negative conventional CFTR testing indicates that the phenotype should be re-evaluated.

Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes.

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

Cystic Fibrosis-Related Diabetes Workshop: Research Priorities Spanning Disease Pathophysiology, Diagnosis, and Outcomes.

Cystic fibrosis (CF) is a recessive disorder arising from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) protein. CFTR is expressed in numerous tissues, with high expression in the airways, small and large intestine, pancreatic and hepatobiliary ducts, and male reproductive tract. CFTR loss in these tissues disrupts regulation of salt, bicarbonate, and water balance across their epithelia, resulting in a systemic disorder with progressive organ dysfunction and damage. Pancreatic exocrine damage ultimately manifests as pancreatic exocrine insufficiency that begins as early as infancy. Pancreatic remodeling accompanies this early damage, during which abnormal glucose tolerance can be observed in toddlers. With increasing age, however, insulin secretion defects progress such that CF-related diabetes (CFRD) occurs in 20% of teens and up to half of adults with CF. The relevance of CFRD is highlighted by its association with increased morbidity, mortality, and patient burden. While clinical research on CFRD has greatly assisted in the care of individuals with CFRD, key knowledge gaps on CFRD pathogenesis remain. Furthermore, the wide use of CFTR modulators to restore CFTR activity is changing the CFRD clinical landscape and the field's understanding of CFRD pathogenesis. For these reasons, the National Institute of Diabetes and Digestive and Kidney Diseases and the Cystic Fibrosis Foundation sponsored a CFRD Scientific Workshop, 23-25 June 2021, to define knowledge gaps and needed research areas. This article describes the findings from this workshop and plots a path for CFRD research that is needed over the next decade.

Heritability of respiratory infection with Pseudomonas aeruginosa in cystic fibrosis.

OBJECTIVE: To quantify the relative contribution of factors other than cystic fibrosis transmembrane conductance regulator genotype and environment on the acquisition of Pseudomonas aeruginosa (Pa) by patients with cystic fibrosis. STUDY DESIGN: Lung infection with Pa and mucoid Pa was assessed using a co-twin study design of 44 monozygous (MZ) and 17 dizygous (DZ) twin pairs. Two definitions were used to establish infection: first positive culture and persistent positive culture. Genetic contribution to infection (ie, heritability) was estimated based on concordance analysis, logistic regression, and age at onset of infection through comparison of intraclass correlation coefficients. RESULTS: Concordance for persistent Pa infection was higher in MZ (0.83; 25 of 30 pairs) than DZ twins (0.45; 5 of 11 pairs), generating a heritability of 0.76. Logistic regression adjusted for age corroborated genetic control of persistent Pa infection. The correlation for age at persistent Pa infection was higher in MZ twins (0.589; 95% CI, 0.222-0.704) than in DZ twins (0.162; 95% CI, -0.352 to 0.607), generating a heritability of 0.85. CONCLUSION: Genetic modifiers play a significant role in the establishment and timing of persistent Pa infection in individuals with cystic fibrosis.

The role of genetic modifiers, inflammation and CFTR in the pathogenesis of Cystic fibrosis related diabetes.

Cystic fibrosis related diabetes (CFRD) generally reflects insufficient and/or delayed production of insulin, developing slowly over years to decades. Multiple mechanisms have been implicated in the pathogenesis of CFRD. CFTR function itself is a strong determinant of CFRD risk. Variants in CFTR that result in residual CFTR function and exocrine pancreatic sufficiency reduce the risk of CFRD by ten to twenty fold. Two groups of hypotheses have been proposed for the mechanism of CFTR impairing insulin secretion in CFRD: (1) ß-cell dysfunction results from ß cell intrinsic CFTR-dependent mechanisms of insulin secretion. (2) ß-cell dysfunction results from factors outside the ß cell. Genome-wide association studies have identified multiple susceptibility genes for type 2 diabetes, including TCF7L2, CDKN2A/B, CDKAL1, and IGF2BP2, as containing genetic modifiers of CFRD. These findings support the presence of intrinsic ß cell defects playing a role in CFRD pathogenesis. Oxidative stress and inflammation are ß cell-extrinsic mechanisms involved with CFRD. CFTR mutations render ß cells more susceptible to oxidative stress and also leads to defects in α-cell function, resulting in reduced suppression of glucagon secretion. Furthermore, CFRD is characterized by ß cell loss secondary to intra-islet inflammation. Recent studies have demonstrated the presence of multiple inflammatory mediators within the human CF islet. This review presents a concise overview of the current understanding of genetic modifiers of CFRD, oxidative stress, islet inflammation, and the controversies about the role of CFTR in the islet.

Complete CFTR gene sequencing in 5,058 individuals with cystic fibrosis informs variant-specific treatment.

BACKGROUND: Cystic fibrosis (CF) is a recessive condition caused by variants in each CF transmembrane conductance regulator (CFTR) allele. Clinically affected individuals without two identified causal variants typically have no further interrogation of CFTR beyond examination of coding regions, but the development of variant-specific CFTR-targeted treatments necessitates complete understanding of CFTR genotype. METHODS: Whole genome sequences were analyzed on 5,058 individuals with CF. We focused on the full CFTR gene sequence and identified disease-causing variants in three phases: screening for known and structural variants; discovery of novel loss-of-function variants; and investigation of remaining variants. RESULTS: All variants identified in the first two phases and coding region variants found in the third phase were interpreted according to CFTR2 or ACMG criteria (n = 371; 16 [4.3%] previously unreported). Full gene sequencing enabled delineation of 18 structural variants (large insertions or deletions), of which two were novel. Additional CFTR variants of uncertain effect were found in 76 F508del homozygotes and in 21 individuals with other combinations of CF-causing variants. Both causative variants were identified in 98.1% (n = 4,960) of subjects, an increase of 2.3 percentage points from the 95.8% (n = 4,847) who had a registry- or chart-reported disease-causing CFTR genotype. Of the remaining 98 individuals, 78 carried one variant that has been associated with CF (CF-causing [n = 70] or resulting in varying clinical consequences n = 8]). CONCLUSIONS: Complete CFTR gene sequencing in 5,058 individuals with CF identified at least one DNA variant in 99.6% of the cohort that is targetable by current molecular or emerging gene-based therapeutic technologies.