Sheelagh Martin

The cystic fibrosis transmembrane conductance regulator gene and ion channel function in patients with idiopathic pancreatitis

Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations are associated with cystic fibrosis (CF)-related monosymptomatic conditions, including idiopathic pancreatitis. We evaluated prospectively enrolled patients who had idiopathic recurrent acute pancreatitis or idiopathic chronic pancreatitis, healthy controls, CF heterozygotes, and CF patients (pancreatic insufficient or sufficient) for evidence of CFTR gene mutations and abnormalities of ion transport by sweat chloride and nasal potential difference testing. DNA samples from anonymous blood donors were controls for genotyping. At least one CFTR mutation or variant was carried in 18 of 40 patients (45%) with idiopathic chronic pancreatitis and in 6 of 16 patients (38%) with idiopathic recurrent acute pancreatitis but in only 11 of the 50 controls (22%, P=0.005). Most identified mutations were rare and would not be identified in routine genetic screening. CFTR mutations were identified on both alleles in six patient (11%). Ion transport measurements in patients with pancreatitis showed a wide range of results, from the values in patients with classically diagnosed CF to those in the obligate heterozygotes and healthy controls. In general, ion channel measurements correlated with the number and severity of CFTR mutations. Twelve of 56 patients with pancreatitis (21%) fulfilled current clinical criteria for the diagnosis of CF, but CFTR genotyping alone confirmed the diagnosis in only two of these patients. We concluded that extensive genotyping and ion channel testing are useful to confirm or exclude the diagnosis of CF in the majority of patients with idiopathic pancreatitis.

Heterogeneity of reproductive tract abnormalities in men with absence of the vas deferens: role of cystic fibrosis transmembrane conductance regulator gene mutations

OBJECTIVE To determine if the types of reproductive tract abnormalities linked to absence of the vas deferens varies with the cystic fibrosis transmembrane conductance regulator (CFTR) genotype. DESIGN Prospective data gathering. SETTING University infertility clinic. PATIENT(S) Forty-six infertile men with absence of the scrotal vas deferens and no signs of cystic fibrosis. INTERVENTION(S) All had blood taken for CFTR gene analysis, 33 had scrotal ultrasounds, and 25 had transrectal ultrasounds. MAIN OUTCOME MEASURE(S) The frequency of testicular, seminal vesicle, and ampullae of the vas deferens malformations was compared between subgroups of men with two, one, or no CFTR gene mutations. RESULT(S) None (0 of 21) of the men with at least one CFTR gene mutations had normal ampullae of the vas or seminal vesicles bilaterally. Two (50%) of 4 men with no CFTR gene mutations had normal ampullae of the vas deferens bilaterally, and 50% had normal bilateral seminal vesicles (statistically significantly different). There was no correlation between testicular malformations and CFTR genotype. CONCLUSION(S) This study indicates that the severity of the malformations in the testis is unrelated to the CFTR genotype, whereas the frequency and severity of wolffian duct malformations are related directly to the CFTR genotype.

Comparing the American and European diagnostic guidelines for cystic fibrosis: same disease, different language?

Background The American and European cystic fibrosis (CF) guidelines recommend different diagnostic criteria. This study assessed diagnostic concordance between these recommendations. Methods Subjects with single organ manifestations suggestive of CF (chronic sinopulmonary disease (RESP), chronic/recurrent pancreatitis (PANC) or obstructive azoospermia (AZOOSP)) were prospectively evaluated by sweat test, nasal potential difference and genotyping. Concordance in diagnostic outcomes between the two algorithms was measured using observed agreement and κ statistics. Results A total of 208 subjects were evaluated. Observed agreement was 84.8% and level of agreement was excellent (κ=0.87) between the American and European recommendations. The RESP phenotype was associated with the highest degree of concordance (observed agreement ≥90%, κ=0.92) compared with the PANC (observed agreement 86%, κ=0.65) and AZOOSP (observed agreement 80%, κ=0.87) phenotypes. Incorporation of nasal potential difference into the American algorithm failed to improve the overall degree of concordance (good agreement level; κ=0.75); the level of agreement was unchanged in RESP and PANC subjects, but reduced in AZOOSP subjects (from excellent to good). Extensive genotyping had limited clinical utility in the diagnosis of CF in both algorithms. Conclusions Despite inconsistencies between the American and European diagnostic recommendations, concordance in diagnostic outcomes among subjects presenting with single organ manifestations of CF was good to excellent. These diagnostic guidelines provide guidance and promote rigorous evaluation for the diagnosis of CF but neither guideline should be regarded as dogma.

Does extensive genotyping and nasal potential difference testing clarify the diagnosis of cystic fibrosis among patients with single-organ manifestations of cystic fibrosis?

Background The phenotypic spectrum of cystic fibrosis (CF) has expanded to include patients affected by single-organ diseases. Extensive genotyping and nasal potential difference (NPD) testing have been proposed to assist in the diagnosis of CF when sweat testing is inconclusive. However, the diagnostic yield of extensive genotyping and NPD and the concordance between NPD and the sweat test have not been carefully evaluated. Methods We evaluated the diagnostic outcomes of genotyping (with 122 mutations included as disease causing), sweat testing and NPD in a prospectively ascertained cohort of undiagnosed patients who presented with chronic sino-pulmonary disease (RESP), chronic/recurrent pancreatitis (PANC) or obstructive azoospermia (AZOOSP). Results 202 patients (68 RESP, 42 PANC and 92 AZOOSP) were evaluated; 17.3%, 22.8% and 59.9% had abnormal, borderline and normal sweat chloride results, respectively. Only 17 (8.4%) patients were diagnosable as having CF by genotyping. Compared to sweat testing, NPD identified more patients as having CF (33.2%) with fewer borderline results (18.8%). The level of agreement according to kappa statistics (and the observed percentage of agreement) between sweat chloride and NPD in RESP, PANC and AZOOSP subjects was ‘moderate’ (65% observed agreement), ‘poor’ (33% observed agreement) and ‘fair’ (28% observed agreement), respectively. The degree of agreement only improved marginally when subjects with borderline sweat chloride results were excluded from the analysis. Conclusions The diagnosis of CF or its exclusion is not always straightforward and may remain elusive even with comprehensive evaluation, particularly among individuals who present at an older age with single-organ manifestations suggestive of CF.

Role of Cystic Fibrosis Transmembrane Conductance Regulator in Patients With Chronic Sinopulmonary Disease

BACKGROUND Previous studies report a high frequency of mutations in the cystic fibrosis (CF) transmembrane conductance regulator gene (CFTR) in patients with idiopathic bronchiectasis. However, most studies have based their findings on preselected patient groups or have performed limited testing for CF transmembrane conductance regulator (CFTR) dysfunction. The objective of our study was to evaluate the prevalence of CFTR gene mutations and/or CFTR-related ion channel abnormalities among subjects with idiopathic chronic sinopulmonary disease and the prevalence of CF or a CFTR-related disorder in this population. METHODS We evaluated 72 prospectively enrolled patients from 1995 to 2005 at the Hospital for Sick Children and St. Michael’s Hospital with idiopathic chronic sinopulmonary disease for evidence of CFTR-mediated abnormalities. We performed CFTR genotyping and assessed CFTR function using sweat testing and nasal potential difference testing. The results were compared with data from healthy control subjects, CF heterozygotes, and patients with CF. RESULTS The CFTR functional tests in idiopathic sinopulmonary patients showed a continuous spectrum, ranging from normal to values typically seen in individuals with CF. Forty-eight patients (66%) demonstrated CFTR mutations and/or abnormalities of CFTR function. Twenty-two (31%) fulfilled criteria for a diagnosis of CF and 26 (36%) for a CFTR-related disorder with a strong female preponderance. Functional tests, more than genotyping, were instrumental in establishing a CF diagnosis. Clinical features failed to distinguish subjects with CF from those with CFTR-related or idiopathic disease. CONCLUSIONS The high prevalence of CF and CFTR dysfunction among patients with idiopathic chronic sinopulmonary disease underscores the need for extensive diagnostic evaluation for CF.

Does Integration of Various Ion Channel Measurements Improve Diagnostic Performance in Cystic Fibrosis

RATIONALE The diagnosis of cystic fibrosis (CF) may remain inconclusive despite comprehensive evaluation. OBJECTIVES Determine whether combined ion channel measurements (C-ICMs) obtained from different end-organ epithelia can help diagnose CF. METHODS Prospective enrollment of (1) a training sample of 156 non-CF subjects and 107 patients with CF, and (2) a validation cohort of 202 patients with single-organ CF-like phenotypes. All subjects had genotyping, sweat test, and nasal potential difference (NPD). Principal components analysis was applied to derive various candidate C-ICMs by combining sweat chloride plus every one or two combination(s) of four NPD parameters (maximal potential difference [MaxPD], change in potential difference in response to perfusion with amiloride [ΔAmil], change after chloride-free and isoproterenol perfusion [ΔCl-free+Iso], and total change in potential difference [ΔAmil+Cl-free+Iso]). MEASUREMENTS AND MAIN RESULTS The best of the 10 candidate C-ICMs, which combined sweat chloride and two NPD parameters (ΔCl-free+Iso and ΔAmil+Cl-free+Iso), diagnosed CF in the training sample with 100% sensitivity and specificity (CF cutoff > 0). In the validation cohort, C-ICM was normal in all subjects with normal sweat test and normal/borderline NPD, with the exception of one subject. C-ICM was abnormal in all subjects when the sweat test was abnormal and the NPD was abnormal/borderline, and when the sweat test was borderline and the NPD was abnormal. C-ICM was abnormal in 75 and 85.7% of subjects with normal sweat chloride plus abnormal NPD, and those with abnormal sweat test plus normal NPD, respectively. In borderline sweat test cases, 23.5, 90, and 100% of subjects had abnormal C-ICM with normal, borderline, and abnormal NPD, respectively. CONCLUSIONS The concept of combining different measures of cystic fibrosis transmembrane conductance regulator function into a single composite score is feasible. The C-ICM may be useful for diagnostic determination of patients with questionable CF.

CYSTIC FIBROSIS GENE MUTATIONS AND INFERTILE MEN WITH PRIMARY TESTICULAR FAILURE

It has been proposed that the gene responsible for cystic fibrosis, called the cystic fibrosis transmembrane conductance regulator (CFTR) gene, may play an important role in the process of spermatogenesis. A group of azoospermic men with primary testicular failure underwent CFTR mutation analysis, including assessment of the intron 8 polythymidine tract (IVS8-T tract). An association was not found between CFTR mutations or the 5T variant of the IVS8-T tract and the primary testicular failure phenotype. This finding suggests that CFTR does not play a significant role in the aetiopathogenesis of primary spermatogenic dysfunction. Therefore, the abnormal testicular histological findings in some post-pubertal men with cystic fibrosis may be a result of nutritional deficiency or testicular obstruction rather than a primary defect in spermatogenesis. In addition, the decreased sperm count in oligozoospermic men with CFTR mutations may be secondary to partial reproductive tract obstruction and not abnormal spermatogenesis. Lastly, routine screening of men with primary testicular failure for CFTR gene mutations is not warranted.