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.     

Carrier screening for Gaucher disease in couples of mixed ethnicity

With the advent of mutational analysis for Gaucher disease, carrier screening has been incorporated into many Jewish genetic disease screening programs. Frequencies and mutations for Gaucher disease in non-Jewish populations are less well established and the detection rate of carriers are lower. Testing is problematic for resolving residual risk in a couple of mixed ethnicity. We report the testing choices made by 20 consecutive couples of mixed ethnicity where the Ashkenazi Jewish partner was identified to be a Gaucher disease gene carrier. Carrier studies of the non-Jewish partner were elected as follows: DNA studies alone, 5 (25%); enzymatic assay, 2 (10%); both, 6 (30%); no carrier studies, 7 (35%). Of the 7 couples not electing carrier studies, one was not in a pregnancy and 6 elected prenatal diagnosis in lieu of parental testing by enzymatic analysis of amniocytes. One couple elected parental carrier studies as well as prenatal diagnosis. All couples electing prenatal Gaucher determination had amniocentesis for other indications as well (4, advanced maternal age; 4, parental anxiety). We conclude that Gaucher screening is feasible for couples of mixed ethnicity if appropriate counseling and testing are offered.     

Carrier screening for cystic fibrosis in a prenatal setting

Maternal prenatal cystic fibrosis (CF) screening was offered from September, 1997, to April, 1999, at the Ghent University Hospital, to couples undergoing prenatal diagnosis (amniocentesis) for reasons not related to CF. Fifteen minutes were devoted to explaining CF, CF screening, and the study protocol. The purpose was to assess the short- and long-term knowledge of CF, the attitude towards carrier screening, and carriership. A total of 314 couples entered the pilot study; 13 female CF carriers were identified. None of their partners carried an identifiable mutation. Our survey results show that information about CF and CF screening can be given effectively as part of antenatal care because most couples recalled important medical and genetic issues, valued the genetic test for CF, and seemed to cope well with the results. Risk estimates and actual numbers were more difficult to process and recall. From the small number of couples in which the woman alone was found to be a carrier, there was little or no evidence of marked distress.     

Molecular screening of partners of cystic fibrosis heterozygotes.

We have screened 100 partners of known or suspected CF heterozygotes for ten CF mutations which account for 88% of the CF mutations seen by us on CF chromosomes. We have identified six CF heterozygotes amongst the 100 low-risk people screened. As two of the six people at high-risk of being CF carriers were subsequently shown not to be CF carriers this gave rise to four couples with a one in four risk of CF in a pregnancy and so far to two PND's. The risk of CF in the remaining 94 couples was reduced to less than one in 800. We have concentrated on the screening of partners for the commoner CF mutations rather than haplotyping them for the CF linked markers XV-2c/TaqI and KM19/PstI which are in linkage disequilibrium with CF. For individuals shown not to carry these ten mutations, a five fold difference in risk of being a CF carrier remains between those who have the XV-2c/KM19 genotypes associated with the highest risk(BB), as compared to those with the lowest risk(CC). Nevertheless we feel that effort is better expended in mutation screening rather than haplotyping.     

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.     

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.     

Acceptability of carrier screening for cystic fibrosis during pregnancy in a German population

A pilot project offering voluntary heterozygote screening for the F508 mutation causing cystic fibrosis (CF) to 638 pregnant women attending two antenatal clinics in the eastern part of Berlin was carried out from 1990–1993. Participation was invited using an information leaflet and inclusion in the study was conditional on written informed consent. Of those invited to participate, only one refused to be tested, on the grounds of non-acceptance of prenatal diagnosis. Eighteen pregnant women were identified as carriers of the F508 mutation. All of them and their male partners accepted counselling in which the genetics of CF, its prognosis and treatment were explained, with emphasis on the meaning of heterozygosity, the fact that carriers are healthy, and the risk of an affected fetus when only one parent is identified as a heterozygote. All partners agreed to be tested for the F508 R553X and G551D mutations and a second counselling session was carried out after this test result was available. No problems were observed during initial testing but, as in other studies, we found considerable anxiety on being given the result in all couples where the woman tested positive; this was reduced substantially by counselling and when the partner tested negative. All probands found to be carriers stated that they found screening acceptable. In contrast to the cautious statement by the German Berufsverband Medizinische Genetik and the hostile reaction from a representative of the CF self-support organisation towards community-based heterozygote screening for CF, this study shows that CF screening is generally acceptable in this German population and that it is actively taken up by most pregnant women when offered.     

Prenatal screening for cystic fibrosis carriers: an economic evaluation.

The cloning of the CFTR gene has made it technically possible to avert the unwanted birth of a child with cystic fibrosis (CF). Several large trials offering prenatal CF carrier screening suggest that such screening is practical and that identified carriers generally use the information obtained. Therefore, a critical question is whether the cost of such screening is justified. Decision analysis was performed that used information about choices that pregnant women were observed to make at each stage in the Rochester prenatal carrier-screening trial. The cost of screening per CF birth voluntarily averted was estimated to be $1,320,000-$1,400,000. However, the lifetime medical cost of the care of a CF child in today's dollars was estimated to be slightly>$1,000,000. Therefore, despite both the high cost of carrier testing and the relative infrequency of CF conceptions in the general population, the averted medical-care cost resulting from choices freely made are estimated to offset approximately 74%-78% of the costs of a screening program. At present, if it is assumed that a pregnancy terminated because of CF is replaced, the marginal cost for prenatal CF carrier screening is estimated to be $8,290 per quality-adjusted life-year. This value compares favorably with that of many accepted medical services. The cost of prenatal CF carrier screening could fall to equal the averted costs of CF patient care if the cost of carrier testing were to fall to $100.     

Active cascade testing for carriers of cystic fibrosis gene.

OBJECTIVE--To examine the acceptability, practicability, efficiency, and application of active screening for carriers of the cystic fibrosis gene in the extended families of those in whom the disease is present (Cascade screening). DESIGN--Paediatricians and physicians provide details of their affected patients, pedigrees are drawn up, and relatives offered tests after initial contact by the affected nuclear families. Affected patients are genotyped in a laboratory with a special interest in the genetics of cystic fibrosis. SETTING--North Western health region. SUBJECTS--Relatives and partners of 607 people with cystic fibrosis. INTERVENTIONS--Genetic counselling by letter for people found to be carriers; formal genetic counselling and when indicated arrangements for prenatal diagnosis for couples discovered to be carriers. MAIN OUTCOME MEASURES--Number of carrier couples detected; action in pregnancy of detected carrier couples; extent of the uptake of screening by relatives. RESULTS--Of 1563 relatives or partners tested, 15 carrier couples were detected; of nine pregnancies undertaken by these 15, eight had prenatal tests and three terminated pregnancies. An average of 16 people per family have come forward for testing so far. CONCLUSIONS--Cascade screening for carriers of cystic fibrosis is well accepted by relatives, especially on the mother''s side of the family; it is 10 times more efficient in detecting carrier couples than unfocused screening. Detected carrier couples make practical use of the information in pregnancy. Active cascade screening for carriers is effective in cystic fibrosis and widespread application is recommended. These principles could be applied to other recessive disorders.     

Twenty-year outcome analysis of genetic screening programs for Tay-Sachs and beta-thalassemia disease carriers in high schools.

Programs for education, screening, and counseling of senior-high-school students, in populations at high risk for Tay-Sachs and beta-thalassemia diseases, have existed for >20 years in Montreal. Four process and outcome variables are reported here: (i) voluntary participation rates in the high-school cohort; (ii) uptake rates for the screening test; (iii) origin of carrier couples seeking the prenatal diagnosis option in the programs; and (iv) change in incidence of the two diseases. Between 1972 and 1992, we screened 14,844 Ashkenazi-Jewish students, identified 521 HexA-deficient carriers (frequency 1:28), reached 89% of the demographic cohort in the educational component of the program, and achieved 67% voluntary participation in the subsequent screening phase. The corresponding data for the beta-thalassemia program are 25,274 students (mainly of Mediterranean origin) representing 67% of the cohort with 61% voluntary participation in the screening phase (693 carriers; frequency 1:36). From demographic data, we deduce that virtually all the carriers identified in the high-school screening program remembered their status, had their partner tested if they did not already know they were a carrier couple, and took up the options for reproductive counseling/prenatal diagnosis. In Montreal, the current origin of all couples using prenatal diagnosis for Tay-Sachs and beta-thalassemia diseases is the corresponding genetic screening/testing program, whereas, at the beginning of the programs, it was always because there was a history of an affected person in the family. Incidence of the two diseases has fallen by 90%-95% over 20 years; the rare new cases are born (with two exceptions) outside the target communities or to nonscreened couples.     

PCR-based screening for cystic fibrosis carrier mutations in an ethnically diverse pregnant population.

As the most common lethal autosomal recessive disorder in North America, cystic fibrosis (CF) is an obvious candidate for general population carrier screening. Although the identification of the causative gene has made detection of asymptomatic carriers possible, the extreme heterogeneity of its mutations has limited the sensitivity of the available DNA screening tests and has called into question their utility when they are applied to patients with no family history of the disease. The purpose of this study was to determine the technical feasibility, patient acceptance and understanding, and psychosocial impact of large-scale CF carrier screening in an ethnically diverse pregnant population. A total of 4,739 pregnant women attending prenatal clinics located in both an academic medical center and a large HMO were invited in person to participate. Of this group, 3,543 received CF instruction and assessments of knowledge and mood, and 3,192 underwent DNA testing for the six most common CF mutations, by means of a noninvasive PCR-based reverse-dot-blot method. Overall participation rates (ranging from 53% at the HMO to 77% at the academic center) and consent rates for DNA testing after CF instruction (>98%) exceeded those of most other American studies. The PCR-based screening method worked efficiently on large numbers of samples, and 55 carriers and one at-risk couple were identified. Understanding of residual risk, anxiety levels, and overall satisfaction with the program were acceptable across all ethnic groups. Our strategy of approaching a motivated pregnant population in person with a rapid and noninvasive testing method may provide a practical model for developing a larger CF screening program targeting appropriate high-risk groups at the national level, and may also serve as a paradigm for population-based screening of other genetically heterogeneous disorders in the future.     

Lack of interest by nonpregnant couples in population-based cystic fibrosis carrier screening.

We used signs and letters to offer free cystic fibrosis (CF) carrier screening to nonpregnant adults in stable relationships who visited numerous clinical and nonclinical sites in Nashville. A total of 179 individuals (<<1% of those eligible) elected to be tested. To understand this observation, we used questionnaires to assess individuals' attitudes about genetic testing in general and about CF carrier screening in particular (n=873). Participants expressed conflicting views about carrier screening. More than 90% of people thought that genetic testing should at least be available. Most respondents said that the views of their partners and physicians were important in their decision making, and most believed that these others favored genetic testing. Yet, more than two-thirds indicated that such factors as insurability, being "at risk," what they would need to learn, abortion, and religious beliefs were important in their decision making, opinions that mitigated against genetic testing. In particular, one-third feared that carriers would lose their health insurance, one-quarter said that they would have been more interested had they been able to provide DNA by buccal swab rather than by finger stick, and less than one-sixth believed that genetic testing was meddling in God's plan. In the face of both the low level of use of free CF carrier screening by nonpregnant couples when it was not offered in person by health-care professionals and the wide variety of concerns demonstrated, we believe that clinicians should not routinely offer carrier screening to nonpregnant individuals who do not have a family history of CF.     

Carrier screening for beta-thalassemia during pregnancy in India: a 7-year evaluation

AIM: Premarital screening for beta-thalassemia is not widely acceptable in India; hence, we evaluated the effectiveness of antenatal screening and counseling over 7 years. METHODS: 61,935 pregnant women were screened using the single-tube osmotic fragility test during their first antenatal visit. Individuals who were positive were investigated further for diagnosis of beta-thalassemia and other abnormal hemoglobins. Spouses of carrier women were tested whenever available. Couples at risk were given the option of prenatal diagnosis. RESULTS: Only 19% of the women registered at the antenatal clinic in the first trimester of pregnancy, and 14% of the women were positive per the osmotic fragility test; 1020 beta-thalassemia heterozygotes and 213 women with other hemoglobinopathies were identified, majority being in the second and third trimesters. Seven hundred and thirteen (69%) of their husbands could be tested, and 37 couples at risk were identified. Only 15 couples had a prenatal diagnosis done. Four couples with affected fetuses opted for termination of pregnancy. The remaining couples either did not respond after counseling or the pregnancies were advanced for prenatal intervention. CONCLUSION: This first large study shows that antenatal screening is acceptable in India; however, awareness generation is still a primary requisite to make women register early at antenatal clinics and bring their spouses for screening when required.     

A pseudodeficiency allele common in non-Jewish Tay-Sachs carriers: Implications for carrier screening

Deficiency of beta-hexosaminidase A (Hex A) activity typically results in Tay-Sachs disease. However, healthy subjects found to be deficient in Hex A activity (i.e., pseudodeficient) by means of in vitro biochemical tests have been described. We analyzed the HEXA gene of one pseudodeficient subject and identified both a C739-to-T substitution that changes Arg247----Trp on one allele and a previously identified Tay-Sachs disease mutation on the second allele. Six additional pseudodeficient subjects were found to have the C739-to-T mutation. This allele accounted for 32% (20/62) of non-Jewish enzyme-defined Tay-Sachs disease carriers but for none of 36 Jewish enzyme-defined carriers who did not have one of three known mutations common to this group. The C739-to-T allele, together with a "true" Tay-Sachs disease allele, causes Hex A pseudodeficiency. Given both the large proportion of non-Jewish carriers with this allele and that standard biochemical screening cannot differentiate between heterozygotes for the C739-to-T mutations and Tay-Sachs disease carriers, DNA testing for this mutation in at-risk couples is essential. This could prevent unnecessary or incorrect prenatal diagnoses.     

Gène CFTR et infertilité masculine en 2001 Conseil génétique, diagnostic prénatal, diagnostic pré-implantatoire

As the vas deferens is also absent in the majority of CF (cystic fibrosis) males, it has been proposed that CBAVD (Congenital Bilateral Absence of Vas Deferens) males may present an incomplete or mild form of CF. Many studies using more extensive mutation analysis have confirmed the role of CFTR gene defects: 80% of CBAVD patients carry one or two mutations. Each patient with a diagnosis of CBAVD should also be examined for pulmonary and pancreatic signs, and sweat tests should be performed. In couples with CBAVD linked to CFTR mutations, the risk of having children with CF or infertility is increased if the female is also a carrier. The woman should be screened for the most frequent CFTR mutations according to her ethnic background. After screening for 80% of the mutations responsible for CF, the residual risk of being a carrier with negative screening is: Z=h(1?a)/(1?ah)=1/120 considering a carrier frequency of 1/25 in the general population. In the case of positive screening, antenatal diagnosis by chorionic villus sampling may be proposed. However, in some situations it is difficult to predict the phenotypic consequences for the child, particularly when a severe transmutation of a variable allele is identified. As these couples require medically-assisted reproduction techniques, pre-implantation genetic diagnosis appears to be more appropriate than antenatal diagnosis. Only embryos that inherit the non-mutated maternal CFTR allele are replaced in the uterus. Examination of childre born to couples with CBAVD is mandatory: immunoreactive trypsinogen assay at 3 days of age, sweat test at 3 months and clinical examination, especially looking for signs of CF. Identification of CFTR mutations in a CBAVD patient has important consequences for his family. Each sibling has a 50% risk of being a carrier and a 25% risk of inheriting the same genotype. The genetic counsellor must inform these siblings about the possible risk of having CF children if they carry CFTR mutations and if their partner is also a carrier.     

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.     

Rapid Detection of the ACMG/ACOG-Recommended 23 CFTR Disease-Causing Mutations Using Ion Torrent Semiconductor Sequencing

Cystic fibrosis (CF) is one of the most frequently diagnosed autosomal-recessive diseases in the Caucasian population. For general-population CF carrier screening, the American College of Medical Genetics (ACMG)/American College of Obstetricians and Gynecologists (ACOG) have recommended a core panel of 23 mutations that will identify 49–98% of carriers, depending on ethnic background. Using a genotyping technology that can rapidly identify disease-causing mutations is important for high-throughput general-population carrier screening, confirming clinical diagnosis, determining treatment options, and prenatal diagnosis. Here, we describe a proof-of-concept study to determine whether the Ion Torrent Personal Genome Machine (PGM) sequencer platform can reliably identify all ACMG/ACOG 23 CF transmembrane conductance regulator (CFTR) mutations. A WT CF specimen along with mutant DNA specimens representing all 23 CFTR mutations were sequenced bidirectionally on the Ion Torrent 314 chip to determine the accuracy of the PGM for CFTR variant detection. We were able to reliably identify all of the targeted mutations except for 2184delA, which lies in a difficult, 7-mer homopolymer tract. Based on our study, we believe PGM sequencing may be a suitable technology for identifying CFTR mutations in the future. However, as a result of the elevated rate of base-calling errors within homopolymer stretches, mutations within such regions currently need to be evaluated carefully using an alternative method.     

Expected effects of mass screening policies on the frequency of cystic fibrosis homozygotes

We evaluated, by deterministic computer simulation, some effects of a screening programme for carriers of cystic fibrosis mutations. Two different selective regimes (heterozygote advantage and directional selection against recessive homozygotes) and three kinds of response to the screening were simulated. The curves describing the expected decline in the frequency of CF homozygotes allow one to predict some benefits of a screening campaign. In addition, it is shown that a strategy aimed at testing couples, rather than individuals, may become less expensive after only two generations of screening. The main source of uncertainty for a screening programme remains the selection mechanism, namely the existence of some sort of biological advantage for heterozygous carriers of CF mutations. Received: 11 March 1997 / Accepted: 15 May 1997     

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.