Targeted extended cystic fibrosis mutation testing on known and at-risk patients and relatives

This paper reports mathematically derived residual risks of being a carrier or being affected with cystic fibrosis following various screening scenarios to assist in interpreting test results and advising patients. While parental screening with 23 American College of Medical Genetics (ACMG) cystic fibrosis mutations defines the 64% of affected U.S. Caucasian fetuses with two detectable mutations, newborn screening for elevated immunoreactive trypsinogen (IRT) and sweat chloride identifies an additional 36% of affected newborns with zero or one detected mutation. The relatives of these affected newborns with less than two detectable mutations have higher posterior (after) 23 mutation-negative test risks of carrying undetected mutations. These calculations emphasize how knowledge of the mutations in the related affected patient substantially improves upon the quality of after-test advice to patients. Furthermore, negative tests of the partner without a family history and/or more extensive cystic fibrosis transmembrane conductance regulator (CFTR) gene testing also increases the likelihood that a negative report is truly negative. When a newborn patient with zero or one detected CFTR mutation has an inconclusive sweat test result, the sweat test should be repeated before ordering additional often unnecessary CFTR gene sequencing. Given the same composite mutation panel test accuracy, a higher proportion of reported test results would be correct during parental screening than when testing at-risk fetuses or symptomatic newborns. Prenatal and newborn screening would be enhanced substantially by medical professionals offering copies of all positive parental and newborn test reports to the parents to share with their relatives. These principles are likely to be applicable to other genetic diseases as the most common mutation frequencies are reported.     

Cystic fibrosis heterozygote screening in 5,161 pregnant women.

A screening program for cystic fibrosis (CF) heterozygotes was conducted in a large HMO prenatal population, to evaluate the level of interest among eligible patients, the effectiveness of prescreening education, attitudes toward the screening process, psychological effects, and utilization of prenatal diagnosis and its outcomes. The heterozygote identification rate and frequency of specific CFTR mutations were also assessed. Identified carriers were offered genetic counseling and testing of male partners. Prenatal diagnosis was offered if both parents were identified as carriers. A total of 5,161 women underwent carrier testing; 947 others completed survey instruments only. The acceptance rate of screening was high (78%), and pretest education by videotape was generally effective. Adverse psychological effects were not reported. Participants generally found screening to be desirable and useful. Screening identified 142 female heterozygotes, 109 couples in which the male partner was not a carrier, and 7 high-risk couples. The incidence of R117H mutations was much higher than expected. The number of identified carriers was much lower in Hispanics than in Caucasians. We conclude that large-scale prenatal screening for CF heterozygotes in the absence of a family history of CF is an acceptable method for identifying couples at risk for affected fetuses. Sufficient pretest education can be accomplished efficiently, test insensitivity is well accepted, adverse psychological events are not observed, and general patient satisfaction is high.     

Carrier screening for cystic fibrosis among Maryland obstetricians before and after the 1997 NIH Consensus Conference

The 1997 National Institutes of Health (NIH) Consensus Conference on Cystic Fibrosis (CF) testing recommended that carrier screening be offered to all pregnant women and couples planning a pregnancy. We surveyed 492 Maryland Ob-Gyns before and after the consensus conference to: (1) assess whether obstetricians changed their practice regarding CF carrier testing, and (2) identify the factors associated with changing practice patterns, including awareness of the statement, and knowledge about CF. Fifty-six percent (275) responded to the first mail questionnaire and 107 obstetricians responded to both questionnaires. In 1998, only 18% of respondents to the second questionnaire were familiar with the NIH statement, but 43% reported discussing testing with patients with no family history, a significant increase from 1997, when only 20% reported discussing testing. Less than one-third correctly answered six multiple-choice knowledge questions about CF and carrier testing. In multivariate analysis, knowledge and familiarity with the NIH consensus statement were not associated with beginning to discuss CF carrier testing after the CF conference with their patients without a family history.     

Cystic fibrosis carrier testing in early pregnancy by general practitioners.

OBJECTIVE--To assess the feasibility of genetic counselling in general practice by using cystic fibrosis carrier screening at the booking appointment as an integral part of routine antenatal care and as a paradigm for the wider participation of general practitioners in medical genetics. DESIGN--Maternal testing (male partner tested only if woman screens positive) and couple testing for cystic fibrosis carrier status in the antenatal population attending one general practice and, later, in a further six (outreach) practices also. SETTING--Two partner urban training practice (pilot practice) in south Manchester, and six north west practices (two inner city, three urban, one rural dispensing). SUBJECTS--Total practice population of 50,000 (pilot practice plus six outreach practices) with an estimated 500-800 pregnancies per year. MAIN OUTCOME MEASURES--(a) Proportion of carriers of cystic fibrosis identified, counselled, and appropriately managed within the first trimester of pregnancy; (b) questionnaire and interview measures of patient satisfaction and stress. RESULTS--Eleven carriers of cystic fibrosis were detected including one carrier couple. This carrier couple, after extensive counselling, elected to have prenatal diagnosis by chorionic villus biopsy. The fetus was homozygous normal. CONCLUSIONS--General practitioners can successfully integrate genetic counselling and cystic fibrosis carrier screening into the first antenatal booking appointment. When a carrier couple is identified clinical geneticists can help with the discussion of reproductive options, and prenatal diagnosis by chorionic villus biopsy can be completed within the first trimester. The results suggest that general practitioners will have an increasingly important role in medical genetics, subject to continuing evaluation of patient acceptability and stress.     

Offering cystic fibrosis carrier screening to an HMO population: factors associated with utilization.

We offered cystic fibrosis (CF) carrier testing to reproductive-age enrollees in an HMO, in order to determine factors associated with test utilization in a primarily nonpregnant population. Male and female enrollees either were mailed an invitation to have the test after attending an educational session (N = 2,713) or were approached in waiting rooms at the HMO sites and given the opportunity to have the test without making an additional visit (N = 608). Uptake was considerably higher when testing could be obtained without making an additional visit (23.5%) than when attendance at an educational session was required as a prerequisite for having the test (3.7%). Utilization was higher among respondents who were planning children. Caucasians, and those with higher educational attainment. Among respondents planning to have children, individuals with higher tolerance for test uncertainty, lower fear of stigma, and higher perceived risk of being a carrier were significantly more likely to have the test. Testing decisions were not associated with the perceived burden of a child with CF or with the likelihood of aborting for CF. Although utilization of CF carrier testing is relatively low among nonpregnant individuals, uptake is significantly higher when testing can be obtained with minimal effort. Factors associated with the decision to be tested had more to do with implications of being a carrier per se than with the concerns of having a child with CF.     

Linkage disequilibrium, cystic fibrosis, and genetic counseling.

Strong linkage disequilibrium occurs between the cystic fibrosis (CF) locus and polymorphisms detected with the DNA probes XV-2c and KM-19. In a North American population, 86% of CF chromosomes occur with a haplotype which occurs on only 14% of normal chromosomes. An individual homozygous for the highest-risk haplotype has an 81-fold greater probability of carrying a CF allele than does an individual homozygous for the lowest-risk haplotype. The linkage-disequilibrium data can be used for prenatal diagnosis and genetic counseling in CF families. The data are useful in 1-in-4-risk pregnancies when DNA is not available from the propositus and in counseling close relatives of CF families. Serious problems arise with some pregnancies which remain at intermediate risks after analysis, and families are left with difficult decisions. It is not clear that genetic testing for couples at less than 1-in-4 risk is cost-effective or standard care, but use of linkage-disequilibrium data will provide more accurate risk probabilities in a substantial proportion of cases if such testing is carried out. Our results emphasize the need for a specific biological or molecular carrier test. This experience in using linkage-disequilibrium and linkage data in combination for genetic counseling provides a model system for the diagnosis of other disorders.     

Preconception cystic fibrosis carrier couple screening: impact,understanding, and satisfaction

The impact, understanding of test-results, and satisfaction among participating couples in a preconception cystic fibrosis (CF) carrier screening project were assessed 6 months after testing. Questionnaire data were obtained from 17/18 identified carriers, 15 partners of carriers with negative test results, and 794 (73%) other participants. None of the carriers changed their reproductive plans because of their test results. Eight participants were worried about their results, including four carriers. Those who attended a general practitioner (GP) consultation for pretest education were less worried than those who attended an educational session. Seven carriers felt less healthy. Predictors of a correct understanding of test results (correct in 62% of participants) were: positive test results, high level of knowledge of CF, high level of education, attending an educational session, and previously heard of CF. All participants who reported that they were worried, all carriers, and 95% of the other participants said that they would make the same decision to be tested again. Although couples who were educated during a GP consultation were less worried, the results of the study suggest that understanding is more correct in couples attending an educational session. The results further suggest that since satisfaction with the screening was high, worries and feeling less healthy due to the test results are probably not a great burden.     

Frequency of the ΔF508 mutation and flanking marker haplotypes at the CF locus from 167 Czech families

Summary This study analyses distribution patterns of the ΔF508 mutation of the cystic fibrosis transmembrane conductance regulator gene (CFTR) gene and the cystic fibrosis (CF)-linked marker loci MET, D7S23, D7S399, and D7S8 in a sample of 167 (116 complete) CF families from Bohemia and Moravia (Czechoslovakia). DNA typing was performed by polymerase chain reaction amplification, restriction analysis, and agarose or polyacrylamide gel electrophoresis. The frequency of the ΔF508 mutation in this sample is 67% and the frequency of the B haplotype is 77.6% on CF chromosomes. Linkage disequilibrium was found between ΔF508 and all markers tested.     

Cystic fibrosis newborn screening: a pilot study to maximize carrier screening

Newborn screening for cystic fibrosis (CF) is expanding because early diagnosis has been shown to result in improved nutrition and growth. Most newborns identified by a mutation panel have a single detected mutation and require sweat testing to exclude an additional undetected mutation. The resulting identification of CF carrier newborns, although not the primary purpose of screening, has three potential benefits, (1) the detection of trait-trait couples, (2) presymptomatic testing of these couples' previously born children who may have undetected CF, and (3) a carrier parent alerting his/her extended family members to the chance of also being a CF carrier. Reaping each benefit requires genetic counseling of parents and their accepting carrier testing. The purpose of this study was to utilize the sweat testing visit to educate parents about the value of carrier testing for themselves and their blood relatives. We compared special care (genetic counseling after explaining the sweat test result and offering of parental DNA testing, all on the sweat test visit) versus standard care (sweat test result reported by phone to the parents the next day by the newborn's physician, ideally with the recommendation to arrange genetic counseling and parental carrier testing). In the first year of New York State CF screening, 64 newborns with one detected mutation were reported in the nine-county region that includes Rochester. Of these, parents of 39 agreed to participate in the study and to be randomized to special or standard care. Sixty-one parents completed both the initial and 1-year follow-up questionnaires (30 couples and one mother). Of the 61 parents, 23 had carrier testing after the birth of the baby. The frequency of such parental testing was significantly higher in the special care group (17/34 or 50%) than in the standard care group (6/27 or 22%) (p < 0.05). This is the first evidence from a randomized trial that genetic counseling and offering carrier testing to parents on the sweat test visit increases identification of carrier parents. Such identification detects trait-trait parents and facilitates carrier testing among relatives.     

Identification of carriers by screening for delta F508 deletion in a multi-generation cystic fibrosis family

Samples from 30 members of a french cystic fibrosis (CF) family had to be typed with probes for restriction fragment length polymorphisms (RFLPs) known to be linked to the CF gene, to fulfill the expectations of twenty-two low-risk relatives who were asking for carrier testing. Classical linkage-disequilibrium data between KM-19 and XV-2c polymorphisms and the CF locus were not informative enough for some individuals, and other RFLPs had to be analyzed to determine which chromosomes carried the deficient gene in the family. We report the retrospective screening for delta F508 mutation in this extended family to illustrate the drastic improvements that the direct detection of the major mutation responsible for CF has on genetic counselling of relatives of patients with cystic fibrosis.     

Cystic fibrosis carrier population screening in the primary care setting.

To determine the receptivity of prenatal care providers and their patients to carrier testing for cystic fibrosis (CF), we offered free carrier screening, followed by genetic counseling of carriers, to all prenatal care providers in Rochester, NY, for all their female patients of reproductive age, pregnant or not. Of 124 prenatal care providers, only 37 elected to participate, but many of these offered screening only to pregnant women. The acceptance rate among pregnant women was approximately 57%. The most common reasons for accepting screening were to obtain reassurance (50.7%) and to avoid having a child with CF (27.8 %). The most common reasons for declining screening were not intending to terminate a pregnancy for CF (32.4%) and believing that the chance of having a CF child was very low (32.2%). Compared with decliners, acceptors were more likely to have no children, regarded having a child with CF as more serious, believed themselves more susceptible to having such a child, knew more about CF, would be more likely to terminate a pregnancy if the fetus were shown to have CF, and more strongly supported offering CF screening to women of reproductive age. Of 4,879 women on whom results were obtained, 124 were found to be carriers. Of these 124 carriers, the partners of 106 were tested. Of the five at-risk couples, four requested prenatal diagnosis and one requested neonatal diagnosis. No woman found to be a carrier whose partner tested negative requested prenatal diagnosis. Except for the imperfect knowledge of those testing negative, none of the adverse outcomes predicted for CF carrier testing in the general population were observed in this study.     

Quantitative variation in cystic fibrosis-associated proteins in cystic fibrosis patients,carriers, and controls

Summary Serum samples from patients with cystic fibrosis (CF), obligate heterozygotes, and normal controls have been examined by isoelectric focusing (IEF). Our results suggest that cystic fibrosis protein (CFP) is a normal serum protein exhibiting quantitative variation primarily dependent on possession of the CF allele. It is concluded that detection of CFP by IEF is an inappropriate screening test for the CF gene due to lack of specificity.     

Functional characterization of a novel CFTR mutation P67S identified in a patient with atypical cystic fibrosis.

Cystic fibrosis (CF) is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. CFTR serves as a cAMP-stimulated chloride channel in a wide range of epithelial tissues and its dysfunction is a hallmark of CF. Over 1400 mutations in the CFTR gene are known, but functional data exist only for a minority of the mutant channels. The aim of the present study was to functionally characterize a novel CFTR mutation identified in a patient with atypical CF. Full length sequencing of the patient's CFTR gene revealed a homozygous C to T transition at nucleotide position 331 (CCT>TCT), which results in a P67S amino acid substitution. Mutant and wild-type CFTR were heterologously expressed in Xenopus laevis oocytes. CFTR whole-cell currents were studied using the two-electrode voltage-clamp technique. Channel surface expression was assessed by a chemiluminescence assay. Expression of P67S-CFTR resulted in functional CFTR chloride channels. However, the CFTR chloride conductance observed in oocytes expressing the mutant channel averaged only 24% of that in oocytes expressing wild-type CFTR. Similarly, surface expression of the mutant channel was reduced. In contrast, the mutation did not alter the anion selectivity of the channel, and Western blot analysis indicated a similar protein expression level of mutant and wild-type CFTR. Our findings indicate that the P67S mutation reduces CFTR chloride channel function by reducing channel surface expression. The mild disease phenotype of the patient indicates that the residual function of the mutant channel is sufficient to prevent the development of severe CF symptoms.     

Antenatal screening for cystic fibrosis: a trial of the couple model.

OBJECTIVE--To assess the delivery and acceptability of antenatal couple screening for cystic fibrosis. Carrier status was notified only when both members of a partnership had cystic fibrosis alleles and therefore a one in four risk of having an affected child. DESIGN--Mouthwash samples were tested when both partners participated. Results were returned only to positive couples. SETTING--Two large maternity hospitals in Edinburgh. SUBJECTS--Screening was offered to all couples who booked at one of the two hospitals. MAIN OUTCOME MEASURES--(a) The take up of screening, carriers and carrier couples identified, take up of prenatal diagnosis, and numbers of affected fetuses detected; (b) questionnaire measures of patient satisfaction and stress. RESULTS--Screening was offered to 8536 couples. 714 (8.4%) were regarded as ineligible, usually because of late booking or absence of a partner. 1900 (24.3%) of the remainder declined screening. Among the 5922 screened couples, four tested positive--that is, both partners were cystic fibrosis heterozygotes. All four elected to have prenatal diagnosis. There were three terminations of pregnancy because of an affected fetus, one couple having two successive pregnancies with affected fetuses. The participation rate was 76% for eligible couples (5922/7822) and 69% for all couples (5922/8536). Only 89 screened couples (1.5%) requested information on individual carrier status. No anxiety was detected among a cohort of the screened population, and 99% of questioned participants expressed satisfaction with the concept of couple screening. CONCLUSIONS--Antenatal couple screening is a satisfactory and acceptable way of screening for cystic fibrosis and has been adopted as routine in the two trial hospitals.     

Involving consumers in the development of an educational program for cystic fibrosis carrier screening.

Input from consumers of health care was sought in developing an educational program to be provided to individuals who are considering carrier testing for cystic fibrosis (CF). In addition, we assessed the ability of health professionals to predict consumers' priorities with regard to such information. A focus group of six middle school teachers formulated questions that they would ask in trying to decide whether they wanted carrier screening for CF. Then, other adults with (n = 39) and without (n = 60) a family history of CF were presented with the questions and were asked to select the questions in the order in which they would want them answered if offered the carrier test. After each question was answered, they were asked whether they would want the carrier test if it were offered to them. CF clinic staff, clinical geneticists, and genetic counselors (n = 31) were asked to select the questions in the order in which they believed that an adult from the general population would want them answered. There were no differences in the order in which adults with and without a family history of CF would want questions answered. Consumers would want to learn about the carrier test as well as their risk of being a carrier and of having a child with CF, before receiving information on reproductive options and the effect that a child with CF would have on the family. Of the 44% of consumers who changed their mind about wanting screening during the course of selecting questions, 52% did so after the first question that they selected.(ABSTRACT TRUNCATED AT 250 WORDS)     

Teaching about cystic fibrosis carrier screening by using written and video information.

We performed two studies using only written and video materials to educate people about cystic fibrosis (CF) and carrier screening. Participants were randomized to receive written or video materials. All received a brief questionnaire. Subjects in group I (n = 238) were (1) individuals in steady relationships and their partners, (2) > or = 18 years old, and (3) not pregnant. Those who accepted free screening and were not demonstrable carriers were sent a letter explaining their results and another questionnaire. Subjects in group II (n = 108) were parents seeking well child care in a university clinic. The main outcome measures were ability to answer questions correctly about (1) health status of CF carriers and people with CF, (2) the possibility of false-negative results, and (3) for those who had screening, the implications of their own results. Written and video materials were equally effective in conveying information. Prior to screening, subjects answered an average of 86% of questions correctly. Subjects with less formal education answered fewer questions correctly; 60% of those with less than a high school education had adequate knowledge of the health consequences of having CF or being a carrier, compared with > or = 94% of college graduates. Performance improved after screening. Where neither partner was a demonstrable carrier, 88% knew their own and their partner's test results, and 90% indicated that their risk of having a child with CF was not zero. Written and video educational materials can be used without face-to-face counseling to inform most people about carrier screening and their test results. These materials may be less effective for those with lower educational backgrounds.     

Homogeneity of cystic fibrosis in Italy.

In 12 unrelated Italian cystic fibrosis (CF) families the frequencies of four DNA polymorphisms closely linked to the CF gene on chromosome 7 were quite similar to those reported for other population samples. Among the 23 affected children from the 12 families, only one recombinant occurred between the CF gene and the met locus, thus confirming the hypothesis of genetic homogeneity of CF previously suggested by the analysis of consanguineous marriages among 624 couples of CF parents. Chi-square test of association indicates a possible linkage disequilibrium between the CF gene and the DNA polymorphism that is most informative in our sample (pmetH TaqI).     

Exclusion of human chromosome 13q34 as the site of the cystic fibrosis mutation.

We have studied a family in which both cystic fibrosis (CF) and an unbalanced translocation between chromosomes 6 and 13 are found. As CF occurs in the child who is effectively monosomic for the translocated part of the long arm of chromosome 13, it was suggested that the locus of the gene mutation causing CF is on chromosome 13q34. The gene for human coagulation factor X is located at 13q34, and we have found a restriction fragment length polymorphism (RFLP) that is revealed by a cloned cDNA coding for this protein. Linkage analysis in eight CF families shows no evidence of cosegregation between CF and the gene for factor X, strongly suggesting that the locus for the defect causing cystic fibrosis is not at 13q34.     

Identification of three novel mutations (457 TAT→G,D192G,Q685X) in the Slovenian CF patients

Chromosomes from a cohort of 60 Slovenian families, corresponding to the 121 cystic fibrosis (CF) chromosomes available, were fully scanned for mutations in the coding sequence of the cystic fibrosis transmembrane conductance regulator (CFTR) gene (The 60 families yielded 121 CF alleles because the mother of one patient was also affected). This corresponds to the 27 exons and intron/exon boundaries that have been studied in chromosomes carrying unidentified alleles. As a result of this survey 84% of the alleles are now clearly identified and we describe in this paper three novel mutations (457 TATG, D192G, and Q685X).