Pancreatic Sufficient Cystic Fibrosis Research Articles

Changes in Sleep in Children and Adults with Cystic Fibrosis and Primary Ciliary Dyskinesia over Time and after CFTR Modulator Therapy.

Cystic fibrosis (CF) and primary ciliary dyskinesia (PCD) are associated with sleep disturbances affecting quality of life (QOL) in both children and adults. However, little is known about the progression of these complaints over time, and the effect of CFTR modulator (CFTRm) therapies. Participants completed sleep quality (SDSC, PSQI) and quality of life questionnaires (PedQL, QOL-BE) as well as the Epworth sleepiness scale (ESS) at baseline and after 4 years. Medical records were reviewed for clinical data and correlations were sought between sleep, QOL, and clinical parameters. A total of 67 patients (33 pediatric), 37 pancreatic insufficient CF (CF-PI), 15 pancreatic sufficient CF (CF-PS), and 15 PCD patients, completed the study. In adults, global sleep quality decreased from 85.8% (76.2-90.5) to 80.9% (71.4-85.7); (p = 0.009). Analysis by disease cohort showed a significant deterioration only in the CF-PS group. In adults off CFTRm, sleep quality decreased from 85.7% (78.6-88.2) to 80.9% (71.4-87.3); (p = 0.021) and from 85.8% (76.2-92.9) to 76.2% (71.4-85.8); (p = 0.078) in people on CFTRm. Changes in sleep quality and changes in QOL over time were strongly associated with each other. In conclusion sleep quality deteriorates over time, correlates with QOL, and is driven primarily by adults and CF-PS patients. CFTRm has a possible effect on sleep initiation; however, results are mixed, and further long-term studies are required.

227 Fat-soluble vitamin status in patients with pancreatic-sufficient cystic fibrosis

227 Fat-soluble vitamin status in patients with pancreatic-sufficient cystic fibrosis

Nutritional status and lung function in children with pancreatic-sufficient cystic fibrosis

BackgroundThere is a strong association between nutrition and long-term FEV1 in cystic fibrosis (CF), but studies have been driven by data from subjects with pancreatic insufficiency (PI-CF). We thus evaluated the association between body mass index (BMI) and FEV1 percent-predicted (FEV1pp) in children with pancreatic sufficiency (PS-CF) and contrasted it with the association in PI-CF. MethodsWe utilized data from the CF Foundation Patient Registry. The cohort included children born 1995–2010, diagnosed <2 years of age, and who had annualized data on BMI percentile and FEV1pp at ages 6–16 years. Pancreatic status was defined based on pancreatic enzyme replacement therapy. The association between BMI and FEV1 was evaluated using linear and mixed-effects longitudinal regression. ResultsThere were 424 children with PS-CF and 7,849 with PI-CF. The association between BMI and FEV1 differed significantly by pancreatic status: each 10-pct higher BMI was associated with 2% [95%CI = 1.9–2.1] higher FEV1pp in PI-CF, compared to just 0.9% [0.5–1.3] in PS-CF (PINTERACTION < 0.001). Within the at-risk nutritional category (BMI <25pct), each 10-pct higher BMI was associated with 5% higher FEV1pp in PI-CF, but no significant increase in PS-CF. Moreover, in PS-CF, overweight/obesity (BMI ≥85pct) was associated with decreasing FEV1pp. In addition, FEV1pp decline through age 20 years in youth with PS-CF was modest (-0.6% per year) and independent of BMI (BMI*age PINTERACTION = 0.37). ConclusionsIn children with PS-CF, BMI remains an important determinant of lung function. However, it may be less critical to attain a BMI >50th percentile; and BMI ≥85th percentile may be detrimental.

Total pancreatectomy with islet autotransplantation in a pancreatic-sufficient cystic fibrosis patient

For children with Cystic Fibrosis (CF) suffering from acute recurrent pancreatitis (ARP), abdominal pain can be severe, difficult to treat, impair their quality of life, affect participation at school, and can lead to chronic opioid dependence. Total pancreatectomy with islet autotransplantation (TPIAT) is an uncommon treatment that is reserved for refractory cases of ARP. We present a case of a 4 year old female with pancreatic-sufficient CF, refractory ARP, frequent hospital admissions for abdominal pain, and continued growth failure despite gastrostomy tube and parenteral nutrition. One year after successful TPIAT, the patient is insulin-independent, growing well, and has not been re-hospitalized for abdominal pain. To our knowledge, this is the youngest patient with CF to undergo TPIAT for debilitating ARP. With CFTR modulators restoring some pancreatic function, CF clinicians should have increased vigilance for the development of ARP.

Reproductive system status and the algorithm to solve fertility issues in men with cystic fibrosis

Rationale: Cystic fibrosis (CF) is a common hereditary disease related to the CFTR gene mutations and characterized by progression and multiple system involvement (primarily of the digestive tract and / or pulmonary system). Most men with CF are infertile. Due to new therapeutic options, the life expectancy of CF patients has increased, with reproductive issues becoming relevant.Aim: A multifaceted assessment of the reproductive system status and fertility in male patients with CF and improvement of the strategies to resolve their reproduction issues.Materials and methods: This cohort prospective study was performed 2006 to 2018 and included 81 unrelated Russian male patients with confirmed CF, aged from 15 to 69 years (mean age 25.6 ± 7.9 years). Forty two (42) patients had pancreatic sufficient and 39 pancreatic insufficient CF. The patients underwent clinical, andrological, laboratory and instrumental examination (scrotal ultrasonography, standard and biochemical semen examination and hormone levels).Results: Reproductive disorders and semen abnormalities found in CF patients varied from preserved fertility to infertility. The following andrological abnormalities were found: delayed puberty (48%), urological disorders (26%), uni- or bilateral testicular hypoplasia (42%), diffuse lesions and cysts of the epididymis (70%), diffuse lesions /calcifications of the prostate (50%), and decreased testosterone levels (24.2%). Azoospermia was diagnosed in 87.5% of the patients, “moderate” or “mild” pathozoospermia (oligo-/astheno-/teratozoospermia) in 11.1%, and normozoospermia in 1.4% of the patients. There were significant differences between the patients with pancreatic sufficient and pancreatic insufficient CF in the ejaculate volume (1.4 ± 1.5 ml vs. 0.6 ± 0.5 ml; р = 0.006), ejaculate pH (6.7 ± 0.7 vs. 6.1 ± 0.4; р &lt; 0.0001), and sperm concentration (19.6 ± 56.0 Mio/mL vs. 0.001 ± 0.008 Mio/ mL; p = 0.011). Normal ejaculate volume was more frequent (21.1% vs 14.7%; p &gt; 0.05) in patients under the age of 25. No bilateral obstruction of vas deferens was found in 71.4% patients with 3849+10kbC&gt;T mutation. There was a significant difference (p &lt; 0.00001) in the frequency of 3849+10kbC&gt;T mutation between the patients with vas deferens obstruction (9.5%) and without it (93.8%). We developed an algorithm to resolve infertility issues (including assisted reproductive technologies) in male CF patients depending on their fertility / presence and type of pathozoospermia and some other factors that may influence the conception and CF risk in the offspring. We also suggested practical recommendations for the andrological assessment, maintenance of reproductive health, and planning of childbirth in these patients.Conclusion: Male CF patients require a multifaceted assessment of their reproductive system. The prognosis of their reproductive functions, the strategy to maintain their reproductive health and making a decision on childbirth depends on the CF type, the CFTR genotype, the results of semen analysis, and the patient’s age. Pancreatic sufficient CF type, 3849+10kbС&gt;T mutation of the CFTR gene and younger age are favorable factors for potential maintenance of vas deferens patency and male fertility in CF patients.

ANDROLOGY EXAMINATION OF PATIENTS WITH PANCREATIC-SUFFICIENT AND PANCREATIC-INSUFFICIENT CYSTIC FIBROSIS

Introduction. Cystic fibrosis (CF) is common monogenic disease resulted from CFTR gene mutations. A most of CF male patients are infertile due to the obstructive azoospermia, however, the mechanisms of the reduced fertility in male patients without the obstruction of seminal ducts, also as the influence of CFTR genotype on their development is understudied.Objectiveis to assess an influence the effect of CFTR genotype, clinical form of CF and age on men reproductive system organs, fertility, and testosterone level and semen parameters in male patients with CF. Materials and methods. We examined 71 Russian men (17–39 years old, mean 24.9 ± 5.3) with CF (pancreatic-sufficient, n = 34, and pancreatic-insufficient, n = 37). Clinical, andrology, laboratory and instrumental examination, including scrotal ultrasonography, biochemical semen, and hormonal analyses were performed.Results. Testicular hypoplasia was reveled in 40,5 % CF patients. Diffuse alterations of epididymis, of epididymal and/or testicular cysts were detected in 62 % patients; 10 % of the patients presented symptoms of hypogonadism. As many as 88 % patients showed spermiological signs of bilateral obstruction of seminal ducts at the level of the vas deferens and epididymis, aplasia of the seminal vesicles (azoospermia, oligospermia, low pH and fructose level of the ejaculate). Pancreatic-insufficient CF is an unfavorable prognostic sign for the obstruction of vas deferens, morphological changes in the scrotum. Patients until 25 years (23 %) as 3849+10kb C&gt;T mutation’s carriers (72 %) significantly more frequently presented preserved vas deferens.Conclusion. Pancreatic-sufficient CF, young age and 3849+10kbС&gt;T mutation are favorable factors presented preserved vas deferens and the possible fertility in men with CF.

13C-Mixed Triglyceride Breath Test and Fecal Elastase as an Indirect Pancreatic Function Test in Cystic Fibrosis Infants.

The 'gold standard' test for the indirect determination of pancreatic function status in infants with cystic fibrosis (CF), the 72-hour fecal fat excretion test, is likely to become obsolete in the near future. Alternative indirect pancreatic function tests with sufficient sensitivity and specificity to determine pancreatic phenotype need further evaluation in CF infants. Evaluation of the clinical utility of both the noninvasive, nonradioactive C-mixed triglyceride (MTG) breath test and fecal elastase-1 (FE1) in comparison with the 72-hour fecal fat assessment in infants with CF. C-MTG breath test and the monoclonal and polyclonal FE1 assessment in stool was compared with the 72-hour fecal fat assessment in 24 infants with CF. Oral pancreatic enzyme substitution (PERT; if already commenced) was stopped before the tests. Sensitivity rates between 82% and 100% for CF patients with pancreatic insufficiency assessed by both the C-MTG breath test and the FE1 tests proved to be high and promising. The C-MTG breath test (31%-38%) as well as both FE1 tests assessed by the monoclonal (46%-54%) and the polyclonal (45%) ELISA kits, however, showed unacceptably low-sensitivity rates for the detection of pancreatic-sufficient CF patients in the present study. The C-MTG breath test with nondispersive infrared spectroscopy (NDIRS) technique, as well as both FE1 tests, are not alternatives to the fecal fat balance test for the evaluation of pancreatic function in CF infants during the first year of life.

Ivacaftor restores CFTR-dependent sweat gland fluid secretion in cystic fibrosis subjects with S945L alleles

BackgroundTo determine in vivo effects of CFTR modulators on mutation S945L. MethodsWe measured effects of CFTR modulators on CFTR-dependent sweating (‘C-sweat’) in two pancreatic sufficient cystic fibrosis (CF) subjects. S1 (S945L/G542X) took ivacaftor and S2 (S945L/F508del) took ivacaftor+tezacaftor. Sweating was stimulated pharmacologically to produce sequentially both CFTR-independent (methacholine stimulated) M-sweat and C-sweat; and the ratio of these was compared. Sweat secretion was measured with two methods: real time secretory rate quantitative recording and by optically measuring the growth of sweat bubbles under oil from multiple identified glands. ResultsUsing the quantitative recorder, we saw zero C-sweat secretion off-drug, but when on-drug the C-sweat responses for both subjects were comparable to those seen in carriers. The on-drug response was further quantified using the sweat bubble method. Each subject again showed robust C-sweat responses, with C-sweat/M-sweat ratios~half of the ratio determined for a cohort of 40 controls tested under identical conditions. ConclusionThese in vivo results, consistent with prior in vitro findings, indicate that the drug treatments restore near-normal function to S945L-CFTR, and support the use of ivacaftor as a treatment for CF patients who carry this allele.

299 Pancreatic sufficient cystic fibrosis infants presenting with severe electrolyte depletion and metabolic alkalosis

299 Pancreatic sufficient cystic fibrosis infants presenting with severe electrolyte depletion and metabolic alkalosis

Comprehensive semen examination in patients with cystic fibrosis

Introduction. Cystic fibrosis (CF) is a common genetic disorder associated with male infertility. Almost all men with CF are infertile due to obstructive azoospermia. The objective is to evaluate semen parameters, excretion of seminal fluid, and spermatogenesis in CF patients. Materials and methods . We examined 44 male CF patients with pancreatic sufficiency (n = 20) and pancreatic insufficiency (n = 24). Standard semen analysis, quantitative karyological analysis of immature germ cells from ejaculate sediment, biochemical semen analysis (fructose, α-glucosidase, citric acid) were performed. Results. Semen analysis diagnosed azoospermia in 77.3 % patients, severe oligozoospermia (< 1 million/ml) and other diagnoses (oligozoospermia, asthenozoospermia, normozoospermia) in 13.6 % and 9.1 % patients, respectively. The signs of obstruction of the vas deferens and aplasia of seminal vesicles were observed in 91 % patients. Azoospermia, oligospermia, pH <7.0 and low content of fructose in the semen samples result from bilateral obstruction of the vas deferens and aplasia of the seminal vesicles. Conclusion . Cryptozoospermia and immature germ cells, detected in ejaculate sediment in all azoospermic patients with CF, indicated aplasia, but not congenital absence of the vas deferens. The majority of CF patients presented signs of seminal ducts obstruction and impaired spermatogenesis and seminal fluid secretion. In contrast to pancreatic-sufficient CF male patients, pancreatic-insufficient CF patients can be fertile and have no obstruction of seminal ducts and severe pathozoospermia.

Smaller Width of the Pancreatic Duct During Secretin-Enhanced Magnetic Resonance Cholangiopancreatography in Pancreatic-Sufficient Cystic Fibrosis Patients.

New tools are needed in cystic fibrosis (CF) diagnostics in pancreatic-sufficient CF (PS-CF) patients. Secretin-enhanced magnetic resonance cholangiopancreatography (SE-MRCP) allows for improved assessment of the width of the pancreatic duct. Sixteen PS-CF patients and 17 healthy volunteers underwent SE-MRCP. The width of the pancreatic duct in the head, the body, and the tail of the pancreas was measured at the baseline and 1, 2, 3, 5, and 10 minutes after secretin administration. The width of the pancreatic duct in the head of the pancreas did not differ between the groups at the baseline; after 10 minutes of secretin stimulation, it was smaller in PS-CF patients (median, 1.4 mm [first-third quartile, 1.3-2.0] vs 2.2 mm [1.7-2.4], P = 0.008). The area under the curve for discrimination between the 2 groups using this parameter was 0.77 (95% confidence interval, 0.60-0.93). The SE-MRCP identified differences in the width of the pancreatic duct between PS-CF and healthy volunteers. Further improvements of the method are needed to augment its clinical utility.

Reduced β-Cell Secretory Capacity in Pancreatic-Insufficient, but Not Pancreatic-Sufficient, Cystic Fibrosis Despite Normal Glucose Tolerance.

Patients with pancreatic-insufficient cystic fibrosis (PI-CF) are at increased risk for developing diabetes. We determined β-cell secretory capacity and insulin secretory rates from glucose-potentiated arginine and mixed-meal tolerance tests (MMTTs), respectively, in pancreatic-sufficient cystic fibrosis (PS-CF), PI-CF, and normal control subjects, all with normal glucose tolerance, in order to identify early pathophysiologic defects. Acute islet cell secretory responses were determined under fasting, 230 mg/dL, and 340 mg/dL hyperglycemia clamp conditions. PI-CF subjects had lower acute insulin, C-peptide, and glucagon responses compared with PS-CF and normal control subjects, indicating reduced β-cell secretory capacity and α-cell function. Fasting proinsulin-to-C-peptide and proinsulin secretory ratios during glucose potentiation were higher in PI-CF, suggesting impaired proinsulin processing. In the first 30 min of the MMTT, insulin secretion was lower in PI-CF compared with PS-CF and normal control subjects, and glucagon-like peptide 1 and gastric inhibitory polypeptide were lower compared with PS-CF, and after 180 min, glucose was higher in PI-CF compared with normal control subjects. These findings indicate that despite “normal” glucose tolerance, adolescents and adults with PI-CF have impairments in functional islet mass and associated early-phase insulin secretion, which with decreased incretin responses likely leads to the early development of postprandial hyperglycemia in CF.

EPS05.8 Vitamin K status and supplementation in children with cystic fibrosis (CF)

Objectives 1.To establish the prevalence of Vitamin K deficiency [raised plasma Prothrombin In Vitamin K Absence (PIVKA II (>0.2 au/ml)] and suboptimal Vitamin K status (low stores) indicated by a K1 2.To evaluate the effectiveness of age related doses of Vitamin K 1 (Phytomenadione) on a weekly basis to correct low K stores and a daily basis for Vitamin K deficiency. Patients and Methods 36 children with CF [31 patients with PICF and 5 with Pancreatic sufficient CF (PSCF)] had baseline measurements by immunoassay for plasma PIVKA II and Vitamin K1. Those with a low Vitamin K1 level received a weekly dose of Phytomenadione (10 mg for those over 7 years of age and 5 mg for those under 7 years of age) and those with deficiency received a daily dose of Phytomenadione (10 mg for those >7 years of age and 5 mg for those Results Twenty-six children (72%) had a compromised Vitamin K status, with 81% (n = 21) of these children having low vitamin K stores and 19% (n = 5) having deficiency. Of the 26 children 75% were PI and 25% were PS; none of those with PS were deficient. Following a year of supplementation 90% (19) of those receiving weekly Phytomenadione had their low stores corrected and 100% of those on a daily dose had their deficiency corrected. Conclusions This study found that the majority of children with PICF and some with PSCF have low vitamin K stores and this can be corrected using an age related weekly dose of Phytomenadione. Deficiency in PICF can be corrected using a daily age related dose of Phytomenadione.

37 The microbial metagenome of cystic fibrosis lower airways

The use of culture-independent microbiome analysis is expanding our view of respiratory tract infection in Cystic fibrosis (CF). The lower airways of people with CF are colonized with polymicrobial communities of bacteria, viruses, fungi and molds. We investigated the microbial metagenome in 20 exocrine pancreatic insufficient and 10 exocrine pancreatic sufficient CF patients. One to five sputum samples were collected from each patient over a 2-year period. The isolated DNA was sequenced by random whole genome sequencing. The reads were aligned to the human, bacterial, virus, fungi and molds reference genomes. Sequences were normalized by GC content and length reference genome. Analysis of temporal series of specimens indicate that each patient carries a specific signature of microbes in his airways unless drastic interventions were undertaken to eradicate unpleasant pathogens such as Burkholderia spp. The spectrum of bacterial species ranged from metagenomes indistinguishable from a healthy non-CF control to metagenomes dominated by the typical CF pathogens Staphylococcus aureus or Pseudomonas aeruginosa . During exacerbations the relative and absolute abundance of species changed, but not the overall signature. On the average several hundred bacterial and viral species, but just a few fungal species were detected by our pipeline. Five to forty species made up 95% of the bacterial metagenome. Our paradigmatic pilot study demonstrates that whole genome sequencing provides deep insight into the microbial CF lung metagenome. Supported by Mukoviszidose e.V. and the German Center for Lung Research (DZL).

Insulin secretion abnormalities in exocrine pancreatic sufficient cystic fibrosis patients

BackgroundThe aim of this study is to assess insulin secretion in pediatric cystic fibrosis (CF) patients with exocrine pancreatic sufficiency. MethodsGlucose and insulin responses during an oral glucose tolerance test (OGTT) were measured in 146 CF patients. Patients were divided into exocrine sufficient (CF-PS) and insufficient (CF-PI) groups based on pancreatic enzyme usage and fecal elastase. A reference group included healthy, non-diabetic subjects. ResultsAll CF groups showed reduced insulin secretion as measured by insulinogenic index. The CF-PS patients had normal glucose tolerance. There was a direct correlation between BMI z-score and insulin area under the curve. ConclusionPatients with CF have reduced insulin secretion during an OGTT regardless of exocrine pancreatic status. The abnormal insulin secretion in all CF patients may predispose them for glucose intolerance, particularly when challenged by inflammation, infection, or nutritional deficiency. In addition, the diminished insulin secretion may contribute to increased catabolism. Lastly, the CF-related diabetes (CFRD) screening guidelines should be followed by all CF patients regardless of pancreatic status.

CFTR transcription defects in pancreatic sufficient cystic fibrosis patients with only one mutation in the coding region of CFTR

BackgroundPatients with cystic fibrosis (CF) manifest a multisystem disease due to deleterious mutations in each gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). However, the role of dysfunctional CFTR...

Type of CFTR Mutation Determines Risk of Pancreatitis in Patients With Cystic Fibrosis

Different mutations in the cystic fibrosis gene (CFTR) are associated with different functional status of the exocrine pancreas. We investigated whether CFTR genotypes determine the risk of pancreatitis in patients with cystic fibrosis (CF). Patients with pancreatic-sufficient CF were identified from 2 CF population-based databases (N = 277; 62 with pancreatitis and 215 without pancreatitis); patients' genotypes and clinical characteristics were analyzed. The loss of pancreatic function associated with each CFTR genotype was determined based on the pancreatic insufficiency prevalence (PIP) score. Patients with pancreatitis were more likely to have genotypes associated with mild (70%) than moderate-severe (30%) PIP scores (P = .004). The cumulative proportion of patients who developed pancreatitis through to the age of 50 years was significantly greater for genotypes associated with mild (50%) than moderate-severe (27%) PIP scores (P = .006). The genotype associated with mild PIP scores had a hazard ratio of 2.4 for pancreatitis (95% confidence interval, 1.3-4.5; P = .006). Patients with pancreatitis were diagnosed with CF at an older median age than those without pancreatitis (14.9 years [interquartile range, 9.5-27.7] vs 9.3 years [interquartile range, 1.5-21.4]; P = .003) and had lower mean levels of sweat chloride than patients without pancreatitis (74.5 ± 26.2 mmol/L vs 82.8 ± 25.2 mmol/L; P = .03). Specific CFTR genotypes are significantly associated with pancreatitis. Patients with genotypes associated with mild phenotypic effects have a greater risk of developing pancreatitis than patients with genotypes associated with moderate-severe phenotypes. This observation provides further insight into the complex pathogenesis of pancreatitis.

Non‐classic cystic fibrosis associated with D1152H CFTR mutation

Limited knowledge exists on phenotypes associated with the D1152H cystic fibrosis transmembrane conductance regulator (CFTR) mutation. Subjects with a D1152H allele in trans with another CFTR mutation were identified using the French Cystic Fibrosis Registry. Phenotypic characteristics were compared with those of pancreatic insufficient (PI) and pancreatic sufficient (PS) cystic fibrosis (CF) subjects in the Registry (CF cohort). Forty-two subjects with D1152H alleles were identified. Features leading to diagnosis included chronic sinopulmonary disease (n = 25), congenital absence of the vas deferens (n = 11), systematic neonatal screening (n = 4), and genetic counseling (n = 2). Median age at diagnosis was 33 [interquartile range (IQR, 24-41)] years in D1152H subjects. Median sweat chloride concentrations were 43.5 (39-63) mmol/l in D1152H subjects and were markedly lower than in PI and PS CF subjects (p < 0.05). Bronchiectasis was present in 67% of D1152H subjects, but Pseudomonas aeruginosa colonization and pancreatic insufficiency were present in <30% of subjects. Estimated rates of decline in forced expiratory volume in 1 s (FEV(1)) were lower in D1152H subjects vs PI CF subjects (p < 0.05). None of the D1152H subjects identified since 1999 had died or required lung transplantation. When present in trans with a CF-causing mutation, D1152H causes significant pulmonary disease, but all subjects had prolonged survival.

ERGs in children with pancreatic enzyme insufficient and pancreatic enzyme sufficient cystic fibrosis

We recorded scotopic and photopic flash electroretinograms (ERGs) in pediatric subjects with cystic fibrosis, aged 4 to 18 years, who were either pancreatic insufficient (PI) or pancreatic sufficient (PS). The aim of the study was to determine whether vitamin supplementation in the PI group allowed comparable retinal function in these two groups. ERGs were recorded from a mixed-gender group of 41 children and adolescents (4 to 17 years of age) with cystic fibrosis. The subjects were grouped according to pancreatic function into PI (n = 29) and PS (n = 12). Full-field flash ERGs were recorded from one eye using a DTL fiber. The pupil was dilated prior to recording using two drops of 0.5% tropicamide. ISCEV photopic and scotopic stimuli and recording conditions were used. Serum levels of vitamin A, beta carotene and retinol binding protein (RBP) were measured on the day of ERG recording. There was no significant difference in ERG amplitudes or implicit times between PI and PS groups. Vitamin A, beta carotene, and RBP levels were not significantly different across the two groups and were not correlated with implicit times or amplitudes of any of the ERG types recorded here. Similarity of ERGs across the PI and PS cystic fibrosis patient populations tested here suggests that the supplementation protocol applied to these populations allows similar levels of retinal function (as indicated by flash ERG parameters) in the two groups.

Localization studies of rare missense mutations in cystic fibrosis transmembrane conductance regulator (CFTR) facilitate interpretation of genotype-phenotype relationships.

We have been investigating the functional consequences of rare disease-associated amino acid substitutions in the cystic fibrosis transmembrane conductance regulator (CFTR). Mutations of the arginine residue at codon 1070 have been associated with different disease consequences; R1070P and R1070Q with "severe" pancreatic insufficient cystic fibrosis (CF) and R1070W with "mild" pancreatic sufficient CF or congenital bilateral absence of the vas deferens. Intriguingly, CFTR bearing each of these mutations is functional when expressed in nonpolarized cells. To determine whether R1070 mutations cause disease by affecting CFTR localization, we created polarized Madin Darby canine kidney (MDCK) cell lines that express either wild-type or mutant CFTR from the same genomic integration site. Confocal microscopy and biotinylation studies revealed that R1070P was not inserted into the apical membrane, R1070W was inserted at levels reduced from wild-type while R1070Q was present in the apical membrane at levels comparable to wild-type. The abnormal localization of CFTR bearing R1070P and R1070W was consistent with deleterious consequences in patients; however, the profile of CFTR R1070Q was inconsistent with a "severe" phenotype. Reanalysis of 16 patients with the R1070Q mutation revealed that 11 carried an in cis nonsense mutation, S466X. All 11 patients carrying the complex allele R1070Q-S466X had severe disease, while 4 out of 5 patients with R1070Q had "mild" disease, thereby reconciling the apparent discrepancy between the localization studies of R1070Q and the phenotype of patients bearing this mutation. Our results emphasize that localization studies in relevant model systems can greatly assist the interpretation of the disease-causing potential of rare missense mutations.