Genotype analysis and phenotypic manifestations of children with intermediate sweat chloride test results

Comparison of Nasal Potential Difference and Intestinal Current Measurements as Surrogate Markers for CFTR Function

OBJECTIVES

Nasal potential difference (NPD) measurement is part of the diagnostic criteria for cystic fibrosis (CF) and now used routinely as an endpoint in clinical trials of correcting the basic defect in CF. Intestinal current measurement (ICM), measured ex vivo on a rectal biopsy, has been used to study cystic fibrosis transmembrane conductance regulator (CFTR) function but has not been compared to NPD in the same subject in adults and children. The aim of the study is to evaluate the potential usefulness of ICM as a marker of CFTR function for treatment studies compared NPD in patients with CF and in healthy control subjects.

METHODS

ICM and NPD were performed on healthy controls and patients with CF. The healthy adults were individuals undergoing routine screening colonoscopy at the Beth Israel Deaconess Medical Center. The healthy children were undergoing colonoscopy for suspicion of inflammation in Hadassah Hebrew University Medical Center. The CF adults were recruited from Boston Children's Hospital CF Center and CF Center Worcester Mass, the children with CF from Hadassah CF Center.

RESULTS

ICM measurements in healthy control subjects (n = 16) demonstrated a mean (±SE) carbachol response of 16.0 (2.2) μA/cm, histamine response of 13.2 (2.1) μA/cm and a forskolin response of 6.3 (2.0) μA/cm. Basal NPD of -15.9 (1.9) and response to Cl free + isoproterenol of -13.8 (2.0). These responses were inverted in CF subjects (n = 12) for ICM parameters with carbachol response of -3.0 (0.5) μA/cm, histamine -1.0 (0.8) μA/cm and a forskolin response of 0.5 (0.3) and also for NPD parameters; basal NPD of -42.2 (4.3) and response to Cl free + isoproterenol of 4.3 (0.7). Pearson correlation test showed the comparability of ICM and NPD in assessing CFTR function.

CONCLUSIONS

ICM is equivalent to NPD in the ability to distinguish patients with CF from controls and could be used as surrogate markers of CFTR activity in treatment protocols.

Long-term outcomes of children with intermediate sweat chloride values in infancy

OBJECTIVE

To describe the clinical course of children who have intermediate sweat chloride values on initial screening for cystic fibrosis (CF).

STUDY DESIGN

We performed a retrospective review of children with intermediate sweat chloride values (raised immunoreactive trypsinogen/1 copy of p.F508del CF mutation on newborn screening (NBS)/sweat chloride value of 30-59 mmol/L) presenting to The Children's Hospital at Westmead over 15 years. Patients with an intermediate sweat chloride evolving to a formal diagnosis of CF (termed "delayed CF") were matched (2:1) with NBS positive patients with CF (termed "NBS positive CF"). Clinical outcomes were compared.

RESULTS

Fourteen of 29 (48%, 95% CI 0.3-0.66) patients with intermediate sweat chloride value evolved to a diagnosis of CF and were matched with 28 NBS positive patients with CF. Delayed CF had less pancreatic insufficiency (OR 0.06, 95% CI 0.01-0.44, P = .006), less colonization with nonmucoid Pseudomonas aeruginosa (OR 0.04, 95% CI 0.01-0.38, P = .005), milder obstructive lung disease (forced expiratory volume in 1 second/forced vital capacity ratio), and overall disease severity (Shwachman scores) at 10 years (mean difference 5.93, 95% CI 0.39-11.46, P = .04; mean difference 4.72, 95% CI 0.9-8.53, P = .015, respectively). Nutritional outcomes were better at 2 years for delayed CF but did not persist to later ages.

CONCLUSIONS

In this cohort, approximately one-half of infants with intermediate sweat chloride value were later diagnosed with CF. The clinical course of delayed CF was milder in some aspects compared with NBS positive CF. These results emphasize the importance of ongoing follow-up of infants with intermediate sweat chloride values.

Diagnosis of cystic fibrosis in the kindred of an infant with CFTR-related metabolic syndrome: importance of follow-up that includes monitoring sweat chloride concentrations over time

Newly implemented newborn screening (NBS) programs in California have resulted in a large subset of patients in whom at least two cystic fibrosis transmembrane conductance regulator (CFTR) mutations are identified, but subsequent sweat chloride analysis reveals normal or indeterminate values. These patients are diagnosed with CFTR-Related Metabolic Syndrome (CRMS). However, the natural progression and management of these patients are not clearly understood and frequently after the age of 1-year these patients are lost to follow-up with Cystic Fibrosis (CF) Centers. We present the first case of an infant who was referred to Miller Children's Hospital for a NBS positive for CF and subsequent discovery of identical mutations in six of his seven older brothers. Several siblings had positive sweat chloride results on repeat testing after the age of 3 years. We suggest the need for continued follow-up of CRMS in a CF center with diagnostic evaluation including repeat sweat chloride testing, beyond the currently recommended period.

Relationship between sweat chloride, sodium, and age in clinically obtained samples

BACKGROUND

The relationship between sweat electrolytes and age is uncertain, as is the value of measuring sodium or the chloride:sodium ratio.

METHODS

13,785 sweat tests performed over 23 years at one center through the Macroduct collection in clinically obtained samples were analyzed.

RESULTS

Sweat chloride tended to decrease over the first year of life, slowly increase until the fourth decade, then either level off or slightly decrease. In children, sweat sodium overlapped between those with positive and negative sweat tests, but not in adults. If the sweat test was positive, there was a higher likelihood of having a chloride:sodium ratio >1, but most subjects with a ratio >1 did not have CF.

CONCLUSIONS

Sweat chloride and sodium vary with age. Measurement of sweat sodium did not add discriminatory value. The proportion of subjects with a chloride:sodium ratio >1, with or without CF, varied greatly between age ranges.

Physiological measurements confirming the diagnosis of cystic fibrosis: the sweat test and measurements of transepithelial potential difference

Post-natal screening allied with genetic mutation testing has altered our perception of cystic fibrosis (CF) as a clinical entity. Increasingly, infants identified through screening programmes have few or no symptoms or present with atypical forms of the disease. We review how the sweat test has evolved to be the gold standard for confirming the diagnosis of CF and examine its limitations. Other physiological measurements, including nasal potential difference and intestinal current measurement, which might aid in establishing the diagnosis, particularly in patients exhibiting a mild phenotype, are also considered.

Does cystic fibrosis neonatal screening detect atypical CF forms? Extended genetic characterization and 4-year clinical follow-up

The neonatal screening protocol for cystic fibrosis (CF) is based on a first determination of blood immunoreactive trypsin (IRT1), followed by a first level genetic test that includes the 31 worldwide most common mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene (DNA31), and a second determination of blood immunoreactive trypsin (IRT2). This approach identifies, in addition to affected subjects, a high proportion of newborns with hypertrypsinaemia at birth, in whom only one mutation is identified and who have a negative or borderline sweat test and pancreatic sufficiency. Although it has been suggested that hypertrypsinaemia may be caused by a single CFTR mutation, whether such neonates should be merely considered as healthy carriers remains a matter of debate as hypertrypsinaemia at birth may be a biochemical marker of a CFTR malfunction because of a second mild mutation. We analyzed, by means of an extended sequencing protocol, 32 newborns who tested positive at an IRT1/DNA31/IRT2 screening protocol and in whom only one CFTR mutation was found. The results obtained demonstrate that 62.5% of these newborns were also carrying a second mild CFTR mutation. The high proportion of compound heterozygous subjects, combined with the results of a 4-year follow-up in nine of these subjects all of whom displaying initial CF clinical symptoms, suggest that it may be possible to use the IRT1/DNA31/IRT2 protocol of neonatal screening to identify newborns with atypical forms of CF. In view of these findings, an extended genetic search for subjects with compound heterozygosity and a periodic clinical assessment should be considered.

N1303K and IVS8-5T, clinical presentation within a family with atypical cystic fibrosis

The CFTR genotype N1303K/IVS8-5T can cause very mild cystic fibrosis (CF) and congenital bilateral absence of the vas deferens (CBAVD). We report one family consisting of five affected patients in two generations, presenting minor symptoms of CF at different ages, segregating the CFTR mutations N1303K and IVS8-T5-TG13 in trans. Common features were chronic sinopulmonary symptoms and borderline or slightly elevated sweat chloride values. One patient had CBAVD.

Guidelines for implementation of cystic fibrosis newborn screening programs: Cystic Fibrosis Foundation workshop report

Newborn screening for cystic fibrosis offers the opportunity for early intervention and improved outcomes. This summary, resulting from a workshop sponsored by the Cystic Fibrosis Foundation to facilitate implementation of widespread high quality cystic fibrosis newborn screening, outlines the steps necessary for success based on the experience of existing programs. Planning should begin with a workgroup composed of those who will be responsible for the success of the local program, typically including the state newborn screening program director and cystic fibrosis care center directors. The workgroup must develop a screening algorithm based on program resources and goals including mechanisms available for sample collection, regional demographics, the spectrum of cystic fibrosis disease to be detected, and acceptable failure rates of the screen. The workgroup must also ensure that all necessary guidelines and resources for screening, diagnosis, and care be in place prior to cystic fibrosis newborn screening implementation. These include educational materials for parents and primary care providers; systems for screening and for providing diagnostic testing and counseling for screen-positive infants and their families; and protocols for care of this unique population. This summary explores the benefits and risks of various screening algorithms, including complex situations that can occur involving unclear diagnostic results, and provides guidelines and sample materials for state newborn screening programs to develop and implement high quality screening for cystic fibrosis.

ICAM-1 expression on conjunctival epithelial cells in patients with cystic fibrosis

BACKGROUND

Cystic fibrosis is one of the most common lethal genetic conditions. The defect is due to mutations in a gene on chromosome 7, named the cystic fibrosis transmembrane regulator (CFTR), which functions as a chloride channel in epithelial membranes It is presumed that the disease affects all secretory epithelia including the eye. The objective of this study is to investigate the expression of intercellular adhesion molecule-1 (ICAM-1) by conjunctival epithelial cells of patients with cystic fibrosis and the correlation between of the expression of ICAM-1 and the grade of cystic fibrosis severity.

METHODS

Impression cytology specimens were collected in 24 patients with cystic fibrosis. Cells were processed for flow cytometry, by using monoclonal antibodies to ICAM-1.

RESULTS

A significant increase of ICAM-1 expression on epithelial cells was found in patients with cystic fibrosis when compared with normal eyes. A positive correlation between the ICAM-1 expression and severe clinical status of CF patients was also observed.

CONCLUSIONS

Our findings suggest that the inflammation appears to have a role in the pathogenesis of the ocular surface changes in patients with cystic fibrosis. ICAM-1 expression on conjunctival epithelial cells may be a marker of the inflammatory status in cystic fibrosis patients. The method described here reveal good repeatability and reliability for the analysis of the inflammatory markers on conjunctival epithelial cells and can be a useful tool in evaluating of the ocular findings and treatment interventions in patients with cystic fibrosis.

Sweat testing for cystic fibrosis: A review of New Zealand laboratories

BACKGROUND

Evolving diagnostic criteria for cystic fibrosis, broadening of the populations being tested and the need to interpret intermediate sweat test results have imposed a much greater need to standardize the collection and analysis of sweat.

AIM

To identify variations in sweat testing in New Zealand laboratories and compare these with guidelines from the UK and the USA.

METHODS

All laboratories in New Zealand offering sweat testing were identified and data collected from these laboratories by structured questionnaire.

RESULTS

There were no New Zealand laboratories that conformed to either set of guidelines. Inconsistencies were observed in minimum sweat quantities, the nature of the iontophoresis solution, the sweat electrolytes analysed, quoted reference ranges and recommendations made as a consequence of the result.

CONCLUSIONS

Conformity to the guidelines would help to minimize variation in sweat testing in New Zealand. Performance of a sufficient number of tests to maintain expertise is critical, but geographical constraints make patient travel to distant centres difficult in a small, scattered population. A possible solution, where numbers permit, may be the collection of sweat locally, with referral to a major laboratory for analysis. This is only possible with adequate training in collection and follow-up audit of the sweat testing procedure both in the collection and in the analytical phase.

Cystic fibrosis: terminology and diagnostic algorithms

There is great heterogeneity in the clinical manifestations of cystic fibrosis (CF). Some patients may have all the classical manifestations of CF from infancy and have a relatively poor prognosis, while others have much milder or even atypical disease manifestations and still carry mutations on each of the CFTR genes. It is important to distinguish between these categories of patients. The European Diagnostic Working Group proposes the following terminology. Patients are diagnosed with classic or typical CF if they have one or more phenotypic characteristics and a sweat chloride concentration of >60 mmol/l. The vast majority of CF patients fall into this category. Usually one established mutation causing CF can be identified on each CFTR gene. Patients with classic CF can have exocrine pancreatic insufficiency or pancreatic sufficiency. The disease can have a severe course with rapid progression of symptoms or a milder course with very little deterioration over time. Patients with non-classic or atypical CF have a CF phenotype in at least one organ system and a normal (<30 mmol/l) or borderline (30-60 mmol/l) sweat chloride level. In these patients confirmation of the diagnosis of CF requires detection of one disease causing mutation on each CFTR gene or direct quantification of CFTR dysfunction by nasal potential difference measurement. Non-classic CF includes patients with multiorgan or single organ involvement. Most of these patients have exocrine pancreatic sufficiency and milder lung disease. Algorithms for a structured diagnostic process are proposed.

Diagnosis of cystic fibrosis in adults with diffuse bronchiectasis

We assessed the contribution of the sweat test, genotyping and nasal potential difference (NPD) in the diagnosis of cystic fibrosis (CF) in adults with diffuse bronchiectasis (DB). Among 601 adults referred for DB from 1992 to 2001, 46 were diagnosed with CF. The sweat test was positive in 37 patients and normal or intermediate in nine patients. Two CF mutations were identified in 18 patients (39%) by screening for 31 mutations and in 36 patients (78%) after complete genetic analysis. NPD was suggestive of CF in 71% of the patients. The combination of the sweat test and genetic analysis led to the diagnosis of CF in 45 patients. In the nine patients with normal or intermediate sweat test, the diagnosis was confirmed by screening for 31 mutations in five, by complete genetic screening in three, and by NPD in the remaining patient. Searching for CF should start with sweat test. If the sweat test is normal or intermediate, screening for 31 mutations may help to diagnose CF. A complete genetic analysis is indicated when only one mutation is detected and/or when other clinical features, such as obstructive azoospermia or pancreatic insufficiency, are suggestive of CF. NPD measurement is indicated in controversial cases.

Mutations of the cystic fibrosis gene and intermediate sweat chloride levels in children

The incidence of mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in children with intermediate sweat chloride levels is unknown. The results of 2,349 sweat tests performed at two Belgian university hospitals were reviewed. Intermediate chloride concentrations were observed in 98 subjects (4.2%), 68 being younger than 18 years of age. Forty-three children could be traced and their parents agreed to take part in the study. Exhaustive analysis of the CFTR gene disclosed a total of 24 putative mutations (27.9%). Three subjects were found to carry only one CFTR mutation, whereas 10 harbored one mutation on both CFTR genes. These 10 children were investigated in detail. At the time of writing, the mean age (+/-SD) of this group is 8.9 years (+/-4.2 years). Nine children are pancreatic sufficient. Three have been asymptomatic for more than two years, whereas the others display, to different degrees, clinical features suggestive of CF. The sweat chloride concentration is slightly higher in this group (39.4 +/- 5.4 mM) than in subjects without CFTR mutation (35.2 +/- 4.4 mM, p < 0.05). The nasal potential difference was abnormal in five of the nine subjects tested. In this study, 23% of children displaying intermediate sweat chloride levels were found to carry a putative mutation on both CFTR genes.