Diagnosis of Cystic Fibrosis in Screened Populations

OBJECTIVE

Cystic fibrosis (CF) can be difficult to diagnose, even when newborn screening (NBS) tests yield positive results. This challenge is exacerbated by the multitude of NBS protocols, misunderstandings about screening vs diagnostic tests, and the lack of guidelines for presumptive diagnoses. There is also confusion regarding the designation of age at diagnosis.

STUDY DESIGN

To improve diagnosis and achieve standardization in definitions worldwide, the CF Foundation convened a committee of 32 experts with a mission to develop clear and actionable consensus guidelines on diagnosis of CF with an emphasis on screened populations, especially the newborn population. A comprehensive literature review was performed with emphasis on relevant articles published during the past decade.

RESULTS

After reviewing the common screening protocols and outcome scenarios, 14 of 27 consensus statements were drafted that apply to screened populations. These were approved by 80% or more of the participants.

CONCLUSIONS

It is recommended that all diagnoses be established by demonstrating dysfunction of the CF transmembrane conductance regulator (CFTR) channel, initially with a sweat chloride test and, when needed, potentially with newer methods assessing membrane transport directly, such as intestinal current measurements. Even in babies with 2 CF-causing mutations detected via NBS, diagnosis must be confirmed by demonstrating CFTR dysfunction. The committee also recommends that the latest classifications identified in the Clinical and Functional Translation of CFTR project [http://www.cftr2.org/index.php] should be used to aid with CF diagnosis. Finally, to avoid delays in treatment, we provide guidelines for presumptive diagnoses and recommend how to determine the age of diagnosis.

Cystic Fibrosis Diagnostic Challenges over 4 Decades: Historical Perspectives and Lessons Learned

OBJECTIVE

Because cystic fibrosis (CF) can be difficult to diagnose, and because information about the genetic complexities and pathologic basis of the disease has grown so rapidly over the decades, several consensus conferences have been held by the US CF Foundation, and a variety of other efforts to improve diagnostic practices have been organized by the European CF Society. Despite these efforts, the application of diagnostic criteria has been variable and caused confusion.

STUDY DESIGN

To improve diagnosis and achieve standardization in terms and definitions worldwide, the CF Foundation in 2015 convened a committee of 32 experts in the diagnosis of CF from 9 countries. As part of the process, all previous consensus-seeking exercises sponsored by the CF Foundation, along with the important efforts of the European CF Society, were comprehensively and critically reviewed. The goal was to better understand why consensus conferences and their publications have not led to the desired results.

RESULTS

Lessons learned from previous diagnosis consensus processes and products were identified. It was decided that participation in developing a consensus was generally not inclusive enough for global impact. It was also found that many efforts to address sweat test issues were valuable but did not always improve clinical practices as CF diagnostic testing evolved. It also became clear from this review that premature applications of potential diagnostic tests such as nasal potential difference and intestinal current measurement should be avoided until validation and standardization occur. Finally, we have learned that due to the significant and growing number of cases that are challenging to diagnose, an associated continuing medical education program is both desirable and necessary.

CONCLUSIONS

It is necessary but not sufficient to organize and publish CF diagnosis consensus processes. Follow-up implementation efforts and monitoring practices seem essential.

Applying Cystic Fibrosis Transmembrane Conductance Regulator Genetics and CFTR2 Data to Facilitate Diagnoses

OBJECTIVE

As a Mendelian disease, genetics plays an integral role in the diagnosis of cystic fibrosis (CF). The identification of 2 disease-causing mutations in the CF transmembrane conductance regulator (CFTR) in an individual with a phenotype provides evidence that the disease is CF. However, not all variations in CFTR always result in CF. Therefore, for CFTR genotype to provide the same level of evidence of CFTR dysfunction as shown by direct tests such as sweat chloride or nasal potential difference, the mutations identified must be known to always result in CF. The use of CFTR genetics in CF diagnosis, therefore, relies heavily on mutation interpretation.

STUDY DESIGN

Progress that has been made on mutation interpretation and annotation was reviewed at the recent CF Foundation Diagnosis Consensus Conference. A modified Delphi method was used to identify consensus statements on the use of genetic analysis in CF diagnosis.

RESULTS

The largest recent advance in CF genetics has come through the Clinical and Functional Translation of CFTR (CFTR2) project. This undertaking seeks to characterize CFTR mutations from patients with CF around the world. The project also established guidelines for the clinical, functional, and population/penetrance criteria that can be used to interpret mutations not yet included in CFTR2's review.

CONCLUSIONS

The use of CFTR genetics to aid in diagnosis of CF requires that the mutations identified have a known disease liability. The demonstration of 2 in trans mutations known to always result in CF is satisfactory evidence of CFTR dysfunction. However, if the identified mutations are known to be associated with variable outcomes, or have unknown consequence, that genotype may not result in a CF phenotype. In these cases, other tests of CFTR function may help.

Diagnosis of Cystic Fibrosis: Consensus Guidelines from the Cystic Fibrosis Foundation

OBJECTIVE

Cystic fibrosis (CF), caused by mutations in the CF transmembrane conductance regulator (CFTR) gene, continues to present diagnostic challenges. Newborn screening and an evolving understanding of CF genetics have prompted a reconsideration of the diagnosis criteria.

STUDY DESIGN

To improve diagnosis and achieve standardized definitions worldwide, the CF Foundation convened a committee of 32 experts in CF diagnosis from 9 countries to develop clear and actionable consensus guidelines on the diagnosis of CF and to clarify diagnostic criteria and terminology for other disorders associated with CFTR mutations. An a priori threshold of ≥80% affirmative votes was required for acceptance of each recommendation statement.

RESULTS

After reviewing relevant literature, the committee convened to review evidence and cases. Following the conference, consensus statements were developed by an executive subcommittee. The entire consensus committee voted and approved 27 of 28 statements, 7 of which needed revisions and a second round of voting.

CONCLUSIONS

It is recommended that diagnoses associated with CFTR mutations in all individuals, from newborn to adult, be established by evaluation of CFTR function with a sweat chloride test. The latest mutation classifications annotated in the Clinical and Functional Translation of CFTR project (http://www.cftr2.org/index.php) should be used to aid in diagnosis. Newborns with a high immunoreactive trypsinogen level and inconclusive CFTR functional and genetic testing may be designated CFTR-related metabolic syndrome or CF screen positive, inconclusive diagnosis; these terms are now merged and equivalent, and CFTR-related metabolic syndrome/CF screen positive, inconclusive diagnosis may be used. International Statistical Classification of Diseases and Related Health Problems, 10th Revision codes for use in diagnoses associated with CFTR mutations are included.

Cystic Fibrosis Foundation evidence-based guidelines for management of infants with cystic fibrosis

Newborn screening for cystic fibrosis (CF) offers the opportunity for early medical and nutritional intervention that can lead to improved outcomes. Management of the asymptomatic infant diagnosed with CF through newborn screening, prenatal diagnosis, or sibling screening is different from treatment of the symptomatically diagnosed individual. The focus of management is on maintaining health by preventing nutritional and respiratory complications. The CF Foundation convened a committee to develop recommendations based on a systematic review of the evidence and expert opinion. These guidelines encompass monitoring and treatment recommendations for infants diagnosed with CF and are intended to help guide families, primary care providers, and specialty care centers in the care of infants with CF.

Cystic fibrosis pulmonary guidelines: airway clearance therapies

Cystic fibrosis (CF) is a genetic disease characterized by dehydration of airway surface liquid and impaired mucociliary clearance. As a result, there is difficulty clearing pathogens from the lung, and patients experience chronic pulmonary infections and inflammation. Clearance of airway secretions has been a primary therapy for those with CF, and a variety of airway clearance therapies (ACTs) have been developed. Because ACTs are intrusive and require considerable time and effort, it is important that appropriate techniques are recommended on the basis of available evidence of efficacy and safety. Therefore, the Cystic Fibrosis Foundation established a committee to examine the clinical evidence for each therapy and provide guidance for their use. A systematic review was commissioned, which identified 7 unique reviews and 13 additional controlled trials that addressed one or more of the comparisons of interest and were deemed eligible for inclusion. Recommendations for use of the ACTs were made, balancing the quality of evidence and the potential harms and benefits. The committee determined that, although there is a paucity of controlled trials that assess the long-term effects of ACTs, the evidence quality overall for their use in CF is fair and the benefit is moderate. The committee recommends airway clearance be performed on a regular basis in all patients. There are no ACTs demonstrated to be superior to others, so the prescription of ACTs should be individualized. Aerobic exercise is recommended as an adjunctive therapy for airway clearance and for its additional benefits to overall health.

Guidelines for diagnosis of cystic fibrosis in newborns through older adults: Cystic Fibrosis Foundation consensus report

Newborn screening (NBS) for cystic fibrosis (CF) is increasingly being implemented and is soon likely to be in use throughout the United States, because early detection permits access to specialized medical care and improves outcomes. The diagnosis of CF is not always straightforward, however. The sweat chloride test remains the gold standard for CF diagnosis but does not always give a clear answer. Genotype analysis also does not always provide clarity; more than 1500 mutations have been identified in the CF transmembrane conductance regulator (CFTR) gene, not all of which result in CF. Harmful mutations in the gene can present as a spectrum of pathology ranging from sinusitis in adulthood to severe lung, pancreatic, or liver disease in infancy. Thus, CF identified postnatally must remain a clinical diagnosis. To provide guidance for the diagnosis of both infants with positive NBS results and older patients presenting with an indistinct clinical picture, the Cystic Fibrosis Foundation convened a meeting of experts in the field of CF diagnosis. Their recommendations, presented herein, involve a combination of clinical presentation, laboratory testing, and genetics to confirm a diagnosis of CF.

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.

Antioxidants in cystic fibrosis. Conclusions from the CF antioxidant workshop, Bethesda, Maryland, November 11-12, 2003

Although great strides are being made in the care of individuals with cystic fibrosis (CF), this condition remains the most common fatal hereditary disease in North America. Numerous links exist between progression of CF lung disease and oxidative stress. The defect in CF is the loss of function of the transmembrane conductance regulator (CFTR) protein; recent evidence that CFTR expression and function are modulated by oxidative stress suggests that the loss may result in a poor adaptive response to oxidants. Pancreatic insufficiency in CF also increases susceptibility to deficiencies in lipophilic antioxidants. Finally the airway infection and inflammatory processes in the CF lung are potential sources of oxidants that can affect normal airway physiology and contribute to the mechanisms causing characteristic changes associated with bronchiectasis and loss of lung function. These multiple abnormalities in the oxidant/antioxidant balance raise several possibilities for therapeutic interventions that must be carefully assessed.

Guide to bone health and disease in cystic fibrosis

Cystic fibrosis (CF) is the most common genetic disease within the Caucasian population and leads to premature respiratory failure. Approximately 60,000 individuals are currently living with CF in North America and Europe, 40% of whom are adults. The life span of these patients has increased from approximately 2 to 32 yr of age over the last three decades. Bone disease has emerged as a common complication in long-term survivors of CF. Some studies have observed that 50-75% of adults have low bone density and increased rates of fractures. Prevention and treatment of CF-related bone disease must address the myriad risk factors (decreased absorption of fat-soluble vitamins due to pancreatic insufficiency, altered sex hormone production, chronic lung infection with increased levels of bone-active cytokines, physical inactivity, and glucocorticoid therapy) for poor bone health. This review is a condensed and updated summary of the Guide to Bone Health and Disease in Cystic Fibrosis: A Consensus Conference, a statement that evolved from a meeting convened by the Cystic Fibrosis Foundation in May 2002 to address the pathogenesis, diagnosis, and treatment of bone disease in CF. The goal of this conference was to develop practice guidelines for optimizing bone health in patients with CF.

Relationship between hydrocarbon structure and induction of P450: effect on RNA levels

1. Exposure to simple aromatic hydrocarbons has been shown to induce P450-dependent activities and the expression of particular P450 isozymes in a manner related to the molecular structure of the inducing hydrocarbon. In an attempt to identify the structural relationship controlling P450 induction, the effect of hydrocarbon treatment on the RNA levels for specific P450 isozymes was examined. 2. Rats were treated with daily injections of hydrocarbons (benzene, toluene, ethylbenzene, n-propylbenzene, m- and p-xylene) for 3 days, and the effects on specific RNA levels were examined by Northern blot hybridization. 3. Although P4502B1 mRNA was not elevated after hydrocarbon treatment, a significant elevation in 2B2 mRNA was observed after exposure to the larger aromatic hydrocarbons, ethylbenzene and m-xylene. It is interesting to note that despite the substantial elevation of P4502B protein levels, only a small elevation of P4502B1 and 2B2 RNA was observed. 4. P4502C11 mRNA was only suppressed by ethylbenzene administration, despite the depression of 2C11 protein levels by several hydrocarbons. 5. P4501A1 mRNA was not detectable and 2E1 mRNA was not changed by any aromatic hydrocarbon treatment investigated in this study. 6. The data indicate that the levels of mRNA species for a number of P450 isozymes are differentially regulated by exposure to hydrocarbons, and that small changes in hydrocarbon size or isomeric structure can influence the levels of these mRNA species.

Expression analysis of the mixed function oxidase system in rat brain by the polymerase chain reaction

Metabolism of therapeutic drugs in the body by the mixed function oxidase system is an important consideration in the analysis of a drug's effectiveness. P450-dependent metabolism within the brain of a neuro-specific drug may affect the drug's course of action. To determine whether cytochrome P450 was expressed in brain, RNA was isolated from the whole brains of rats treated with a variety of known hepatic P450 inducers, including amitriptyline, imipramine, isosafrole, phenobarbital, and beta-naphthoflavone. The RNA was analyzed for the presence of P450 isozymes by the PCR technique. Differential expression of P450IA1, P450IIB1, P450IIB2, P450IID, and P450IIE1 was detected in the brain samples, depending on the treatment. Cytochrome P450 reductase expression was also detected in the brain samples, giving strong evidence that the brain contains a competent mixed function oxidase system under all conditions studied.

The Saccharomyces cerevisiae SRK1 gene, a suppressor of bcy1 and ins1, may be involved in protein phosphatase function

The Saccharomyces cerevisiae SRK1 gene, when expressed on a low-copy shuttle vector, partially suppresses the phenotype associated with elevated levels of cyclic AMP-dependent protein kinase activity and suppresses the temperature-sensitive cell cycle arrest of the ins1 mutant. SRK1 is located on chromosome IV, 3 centimorgans from gcn2. A mutant carrying a deletion mutation in srk1 is viable. SRK1 encodes a 140-kDa protein with homology to the dis3+ protein from Schizosaccharomyces pombe. The ability of SRK1 to alleviate partially the defects caused by high levels of cyclic AMP-dependent protein kinase and the similarity of its encoded protein to dis3+ suggest that SRK1 may have a role in protein phosphatase function.

Expression of two cytochromes P450 involved in carcinogen activation in a human colon cell line

Cytochrome P450 is known to cause carcinogen activation and correspondingly increased cancer risk in animal models. In order to determine whether P450 in the colon may be involved in cancer development in the human, the human colon cell line LS174T was examined for the presence of various cytochromes P450. Two isozymes of P450 were identified in the human cell line. Expression of P450IA1 or IA2 was increased by treatment of the cell line with benzanthracene; the induction was demonstrated by an increase in RNA hybridizing to a probe for P450IA1 and by ethoxyresorufin deethylation activity. Western analysis of microsomes isolated from human colon tissue also demonstrated the presence of P450IA1, as well as a form which cross-reacted to an antibody to human P450IIC9. Another isozyme, P450IIE1, was identified by polymerase chain reaction amplification of RNA from LS174T cells. These results underscore the presence of cytochromes P450 in colonic tissue and provide a basis for the involvement of isozyme-specific P450 mediated reactions in carcinogenesis of the colon.

Replacement of a conserved proline and the alkaline conformational change in iso-2-cytochrome c

Although point mutations usually lead to minor localized changes in protein structure, replacement of conserved Pro-76 with Gly in iso-2-cytochrome c induces a major conformational change. The change in structure results from mutation-induced depression of the pK for transition to an alkaline conformation with altered heme ligation. To assess the importance of position 76 in stabilizing the native versus the alkaline structure, the equilibrium and kinetic properties of the pH-induced conformational change have been compared for normal and mutant iso-2-cytochrome c. The pKapp for the conformational change is reduced from 8.45 (normal iso-2) to 6.71 in the mutant protein (Gly-76 iso-2), suggesting that conservation of Pro-76 may be required to stabilize the native conformation at physiological pH. The kinetics of the conformational change for both the normal and mutant proteins are well-described by a single kinetic phase throughout most of the pH-induced transition zone. Over this pH range, a minimal mechanism proposed for horse cytochrome c [Davis, L. A., Schejter, A., & Hess, G. P. (1974) J. Biol. Chem. 249, 2624-2632] is consistent with the data for normal and mutant yeast iso-2-cytochromes c: NH KH----N + H+ kcf in equilibrium kcb A NH and N are native forms of cytochrome c with a 695-nm absorbance band, A is an alkaline form that lacks the 695-nm band, KH is a proton dissociation constant, and kcf and kcb are microscopic rate constants for the conformational change. The Gly-76 mutation increases kcf by almost 70-fold, but kcb and KH are unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Replacement of a conserved proline eliminates the absorbance-detected slow folding phase of iso-2-cytochrome c

As a test of the proline isomerization model, we have used oligonucleotide site-directed mutagenesis to construct a mutant form of iso-2-cytochrome c in which proline-76 is replaced by glycine [Wood, L. C., Muthukrishnan, K., White, T. B., Ramdas, L., & Nall, B. T. (1988) Biochemistry (preceding paper in this issue)]. For the oxidized form of Gly-76 iso-2, an estimate of stability by guanidine hydrochloride induced unfolding indicates that the mutation destabilizes the protein by 1.2 kcal/mol under standard conditions of neutral pH and 20 degrees C (delta G degrees u = 3.8 kcal/mol for normal Pro-76 iso-2 versus 2.6 kcal/mol for Gly-76 iso-2). The kinetics of folding/unfolding have been monitored by fluorescence changes throughout the transition region using stopped-flow mixing. The rates for fast and slow fluorescence-detected refolding are unchanged, while fast unfolding is increased in rate 3-fold in the mutant protein compared to normal iso-2. A new kinetic phase in the 1-s time range is observed in fluorescence-detected unfolding of the mutant protein. The presence of the new phase is correlated with the presence of species with an altered folded conformation in the initial conditions, suggesting assignment of the phase to unfolding of this species. The fluorescence-detected and absorbance-detected slow folding phases have been monitored as a function of final pH by manual mixing between pH 5.5 and 8 (0.3 M guanidine hydrochloride, 20 degrees C).(ABSTRACT TRUNCATED AT 250 WORDS)

Construction and characterization of mutant iso-2-cytochromes c with replacement of conserved prolines

Oligonucleotide-directed mutagenesis has been used to construct two mutant forms of iso-2-cytochrome c. In one, Pro-30 is replaced by threonine; in the other, Pro-76 is replaced by glycine. Both prolines are fully conserved among mitochondrial cytochromes c and play important structural and functional roles. Yeast with either the Pro-30 or the Gly-76 mutation has appreciable levels of mutant protein in vivo and grows on media containing nonfermentable carbon sources. Thus, neither mutation blocks protein targeting to mitochondria, uptake by mitochondria, covalent attachment of heme, or in vivo function. As judged by ultraviolet-visible spectrophotometry and proton nuclear magnetic resonance spectroscopy, the nativelike conformation of purified Gly-76 iso-2 at pH 6 is almost indistinguishable from that of the normal protein at pH 6. Ultraviolet second-derivative spectrophotometry, however, suggests an increase in the average number of exposed tyrosine side chains, with 2.25 out of 5 residues exposed for the mutant compared to 1.95 for normal iso-2. Above neutral pH, the protein folds to a mutant conformation possibly related to alkaline cytochrome c. Nuclear Overhauser difference spectroscopy of the reduced nativelike conformation allows assignment of several proton resonances and comparison of side-chain conformations of the heme ligand Met-80 in the mutant and the normal proteins. The proton chemical shifts for the assigned resonances are the same within errors for Gly-76 iso-2 and normal iso-2 at pD 6, 20 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in conformation and slow refolding kinetics in mutant iso-2-cytochrome c with replacement of a conserved proline residue

Using oligonucleotide-directed mutagenesis, we have produced a mutant form of iso-2-cytochrome c of yeast in which threonine (Thr-71) replaces a conserved proline residue (Pro-71) located between two short alpha-helical segments in the native protein. Optical spectroscopy indicates that, at pH 7.2, Thr-71 iso-2-cytochrome c folds to a nonnative conformation possibly related to the alkaline form of the native protein. On titration to pH 5.2, Thr-71 iso-2-cytochrome c regains many of the optical properties of the normal protein. We have shown that the proline residue at position 71 has no effect on the kinetics of fluorescence-detected slow refolding. However, between pH 5 and pH 7.2 the amplitude for absorbance-detected slow folding is strongly pH dependent in the mutant protein but is largely independent of pH in the normal protein. We believe this to be due to the folding of Thr-71 iso-2-cytochrome c to a nonnative conformation at pH 7.2 that does not require the slow, absorbance-detected conformational changes observed in folding to the more native-like state at pH 5-6.

Transformation of a Bacillus subtilis L-form with bacteriophage deoxyribonucleic acid

A stable L-form, sal-1, of Bacillus subtilis was transformed with deoxyribonucleic acid (DNA) from bacteriophages phi 25 and phi 29 to determine whether exogenous DNA can be introduced into this organism. The viral transformation (transfection) was successful with the use of polyethylene glycol. In the presence of the fusogen, bacteriophage phi 25 DNA initiated a single cycle of infection. When compared with transfection of competent cells of Bacillus subtilis, the appearance of viral particles was delayed and their production occurred over a longer time period. L-form cells were best able to support intracellular replication of phi 25 viral particles when in balanced growth in a rich medium. The addition of polyethylene glycol also induced infection of sal-1 with whole bacteriophage phi 25 particles which could not otherwise infect the L-form and enhanced infection by intact phi 29 particles. Primary recombination was shown to be required for polyethylene glycol-mediated phi 25 transfection, but not phi 29 transfection or for whole bacteriophage phi 25 infection mediated by polyethylene glycol. Successful transfection of sal-1 suggests that the L-form may be amenable to genetic modification with exogenous DNA.