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Proportion of Cystic Fibrosis Gene Mutations Not Detected by Routine Testing in Men With Obstructive Azoospermia
Victor Mak, MD, MSc, FRCSC;
Julian Zielenski, PhD;
Lap-Chee Tsui, OC, PhD;
Peter Durie, MD, FRCPC;
Armand Zini, MD, FRCSC;
Sheelagh Martin, RN, BScN;
Teresa Barry Longley, RN;
Keith A. Jarvi, MD, FRCSC
JAMA. 1999;281:2217-2224.
ABSTRACT
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Context Infertile men with obstructive azoospermia may have mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, many of which are rare in classic cystic fibrosis and not evaluated in most routine mutation screening.
Objective To assess how often CFTR mutations or sequence alterations undetected by routine screening are detected with more extensive screening in obstructive azoospermia.
Design Routine screening for the 31 most common CFTR mutations associated with the CF phenotype in white populations, testing for the 5-thymidine variant of the polythymidine tract of intron 8 (IVS8-5T) by allele-specific oligonucleotide hybridization, and screening of all exons through multiplex heteroduplex shift analysis followed by direct DNA sequencing.
Setting Male infertility clinic of a Canadian university-affiliated hospital.
Subjects Of 198 men with obstructive (n=149) or nonobstructive (n=49; control group) azoospermia, 64 had congenital bilateral absence of the vas deferens (CBAVD), 10 had congenital unilateral absence of the vas deferens (CUAVD), and 75 had epididymal obstruction (56/75 were idiopathic).
Main Outcome Measure Frequency of mutations found by routine and nonroutine tests in men with obstructive vs nonobstructive azoospermia.
Results Frequency of mutations and the IVS8-5T variant in the nonobstructive azoospermia group (controls) (2% and 5.1% allele frequency, respectively) did not differ significantly from that in the general population (2% and 5.2%, respectively). In the CBAVD group, 72 mutations were found by DNA sequencing and IVS8-5T testing (47 and 25, respectively; P<.001 and P=.002 vs controls) vs 39 by the routine panel (P<.001 vs controls). In the idiopathic epididymal obstruction group, 24 mutations were found by DNA sequencing and IVS8-5T testing (12 each; P=.01 and P=.14 vs controls) vs 5 by the routine panel (P=.33 vs controls). In the CUAVD group, 2 mutations were found by routine testing (P=.07 vs controls) vs 4 (2 each, respectively; P=.07 and P=.40 vs controls) by DNA sequencing and IVS8-5T testing. The routine panel did not identify 33 (46%) of 72, 2 (50%) of 4, and 19 (79%) of 24 detectable CFTR mutations and IVS8-5T in the CBAVD, CUAVD, and idiopathic epididymal obstruction groups, respectively.
Conclusions Routine testing for CFTR mutations may miss mild or rare gene alterations. The barrier to conception for men with obstructive infertility has been overcome by assisted reproductive technologies, thus raising the concern of iatrogenically transmitting pathogenic CFTR mutations to the progeny.
INTRODUCTION
Cystic fibrosis (CF) is the most common serious autosomal recessive condition in whites, with a prevalence of approximately 1 per 2500 and a carrier frequency of 1 per 25.1 The gene responsible for CF, called the cystic fibrosis transmembrane conductance regulator (CFTR), encodes the cyclic adenosine monophosphate (cAMP)–dependent chloride channel found in the apical membrane of secretory epithelial cells.1 Clinical features of CF include chronic pulmonary obstruction and infections, exocrine pancreatic insufficiency, neonatal meconium ileus, elevated sweat electrolytes, and male infertility.1-2 The vast majority (>95%) of men with CF are azoospermic (absence of spermatozoa in ejaculate) due to anomalies in Wolffian duct-derived structures, with the body and tail of the epididymis, vas deferens, seminal vesicles, and ejaculatory ducts being atrophic or absent.3-6
Studies involving DNA mutation analyses of the CFTR gene have demonstrated that infertile men with obstructive azoospermia from congenital bilateral absence of vas deferens (CBAVD), congenital unilateral absence of vas deferens (CUAVD), or epididymal obstruction have a considerably higher incidence of mutations in the CFTR gene compared with the general population.7-33 The CFTR gene alterations associated with the obstructive azoospermic conditions are described rarely within the classic CF population, or they are considered to be of a mild form, such as the 5-thymidine variant of the polythymidine tract (IVS8-5T) in the splice acceptor site of intron 8.13-15,24, 26-27,29, 31-34 However, most CFTR mutation screening panels test only for the more common mutations associated with CF, thus potentially missing rare CFTR gene alterations or those that may confer or contribute to an obstructive azoospermia phenotype.
Another recent twist is that advances in assisted reproductive technologies with in vitro fertilization–intracytoplasmic sperm injection (in which a single sperm is injected into the cytoplasm of a mature oocyte to obtain a viable embryo) have made it possible for these men to father their own children.35-50 One major concern with this procedure is that the genetic defect inherent in the patient (ie, CFTR mutations) can be iatrogenically transmitted to the offspring.51-56
Many of the articles on the molecular genetics of obstructive azoospermia advocate the evaluation of individuals with this condition and possibly their female partners for mutations or variants in the CFTR gene. However, these studies vary in their methods for detecting mutations. Most investigators have tested for a set of common CFTR mutations associated with the CF phenotype, while others performed a complete screening of all CFTR exons and flanking introns followed by direct sequencing as indicated. The purpose of our study was to assess the significance of evaluating not only common CFTR gene mutations associated with CF but also other alterations or variants using a more extensive screening method to gain insight into whether there is any yield in using such a technique. As outlined above, this issue has important clinical implications in the present era of reproductive options for men with obstructive azoospermia, many of whom may now realize biologic fatherhood due to the advent of successful gamete micromanipulation.
METHODS
Patients and Samples
One hundred sixty-three otherwise healthy male subjects with obstructive azoospermia and 63 otherwise healthy male subjects with nonobstructive azoospermia from primary testicular failure presenting consecutively to the Andrology Clinic at the Mount Sinai Hospital, Toronto, Ontario, between 1995 and 1998, were approached for CFTR genotype analysis after giving informed consent and receiving appropriate genetic counseling. One hundred forty-nine men with obstructive azoospermia and 49 men with nonobstructive azoospermia consented to participate in the study, which was approved by the hospital's institutional review board and the Human Subjects Review Committee of the University of Toronto. A subset of study subjects (n=46) was previously described in an investigation examining the association between anatomic anomalies and CFTR gene mutations.57 Some subjects (n=62) were also previously described with regard to obstructive azoospermia and CFTR genotype.21 Clinical evaluation included history taking, physical examination, semen analysis, and serum hormonal profile (luteinizing hormone, follicle-stimulating hormone, testosterone, and prolactin). Additional investigations such as scrotal and/or transrectal ultrasonography, testicular biopsy, and scrotal exploration were performed as indicated for diagnostic confirmation. Of the 149 obstructive azoospermic subjects, 64 were diagnosed as having CBAVD (51 white, 1 black, 11 Asian, 1 interracial [white/black]), 10 as having CUAVD (7 white, 3 Asian), and 75 as having epididymal obstruction (53 white, 8 black, 13 Asian, 1 interracial [white/Asian]). Of the 49 nonobstructive azoospermic subjects, 41 were white, 1 was black, and 7 were Asian. The racial proportions of our study groups reflected those of the Ontario population.58
CFTR Gene Mutation Analysis
Peripheral venous blood for CFTR genotype analysis was obtained from each of the 198 subjects. Genomic DNA was isolated from lymphocytes according to standard protocols,59 and then subjected to the following molecular evaluations:
- Analysis for 31 of the most common CFTR mutations found within the white CF population,60 consisting of
 F508, W1282X, G542X, G551D, N1303K, R553X, G85E, R117H, S549N, V520F, R334W, A455E, R347P, R1162X, Y122X, S549R, 621+1G T, I507, R560T, R347H, 3659delC, Q493X, 1898+1GT, 711+1GT, 3849+10CT, 1717-1GA, 3849+4AG, 3905insT, 1078delT, 2183AAG, and 2789+5GA. Briefly, the technique involved amplification by polymerase chain reaction61 of the relevant exons, followed by digestion with appropriate restriction endonucleases and acrylamide gel electrophoresis with ethidium bromide staining.
- Investigation for polythymidine tract variant within the intron 8 acceptor splice site; exon 9 including the intron 8 polythymidine tract was polymerase chain reaction amplified with primers located in introns flanking exon 962 and evaluated by allele-specific oligonucleotide hybridization.63
- Extensive screening for CFTR gene sequence alterations; all 27 exons of the CFTR gene and their flanking intron sequences as well as the promoter region were polymerase chain reaction amplified and amplicons were subjected to electrophoresis and heteroduplex shift analysis on Hydrolink gel matrix (FMC Bioproducts, Rockland, Me) in multiplex fashion,64 followed by DNA transfer to a nylon membrane and hybridization with exon-specific radiolabeled oligonucleotides; band shifts and unusual patterns were further characterized by direct sequencing of corresponding CFTR regions.
Statistics
Differences in mutation frequencies between men with the various types of obstructive azoospermia (CBAVD, CUAVD, or idiopathic epididymal obstruction) and men with nonobstructive azoospermia were compared by the  2 statistic or Fisher exact test. All P values were based on 2-sided comparisons and P <.05 indicated statistical significance. Estimates of the proportion of mutations identified by each test were made with 95% confidence intervals (CIs) for proportions using a normal approximation.
RESULTS
CFTR Mutations in Men With Nonobstructive Azoospermia (Control Subjects)
A total of 49 subjects with nonobstructive azoospermia due to primary testicular failure were assessed for CFTR gene mutations (Table 1). Two CFTR mutations (F508, G542X) were identified by analysis using the 31 CFTR mutation panel (Table 2). The IVS8-5T variant was identified in 5 alleles. Two mutations (the identical F508 and G542X mutations detected by the 31 mutation panel) were identified through screening of all CFTR exons and splice sites. The allelic frequency of the IVS8-5T variant was not significantly different between nonobstructive azoospermic subjects (5.1%) and the general population (26 [5.2%] of 498 chromosomes based on data pooled from Kiesewetter et al,63 Cuppens et al,65 Dork et al,66 and Chillon et al13). Also, the carrier frequency of CFTR gene mutations (2 [4%] of 49 subjects) did not differ significantly from the carrier frequency (4%) in the general population.1
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Table 1. Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) Genotypes in Men With Obstructive and Nonobstructive Azoospermia*
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Table 2. Cystic Fibrosis Transmembrane Conductance Regulator Gene Mutations Identified by 3 Screening Methods in Men With Obstructive and Nonobstructive Azoospermia*
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CFTR Mutations in Men With Obstructive Azoospermia
A total of 149 subjects with obstructive azoospermia (64 with CBAVD, 10 with CUAVD, and 75 with epididymal obstruction) were evaluated for mutations in the CFTR gene. The 31 common CF-associated CFTR mutations, the IVS8-5T variant, and the entire coding sequence of the CFTR gene were assessed (Table 1).
For those in the CBAVD group, analysis of the 31 most common CFTR mutations associated with CF led to the identification of 39 mutations in 128 alleles (P<.001 for comparison with the nonobstructive azoospermia group) (Table 2). The mutation most frequently identified was F508 (23 alleles), followed by R117H (9 alleles). Others detected using the 31 mutation panel included W1282X (2 alleles), R334W (2 alleles), S549R (1 allele), R347P (1 allele), and N1303K (1 allele). Twenty-five chromosomes tested positive for the IVS8-5T variant (P<.001 for comparison with the nonobstructive azoospermia group). Forty-seven mutations were detected by screening all CFTR exons for sequence alterations, including the same 39 mutations identified by the routine 31 mutation panel (P<.001 for comparison with the nonobstructive azoospermia group). Of the 8 additional CFTR gene sequence alterations detected using extensive CFTR exon screening, 5 have been described rarely in the CF population (L206W [identified in 2 subjects], P67L, 1677delTA, R117L, and 4016insT).60 One mutation, D979A, was previously identified in a Vietnamese CBAVD patient.60 Interestingly, our CBAVD subject with D979A (also a carrier of IVS8-5T) was of Vietnamese descent as well. The M952T mutation is a previously unreported, novel mutation. Therefore, of the alleles with identifiable CFTR mutations in the CBAVD group, 39 (54%), 25 (34%), and 47 (65%), respectively, were detected by the routine mutation panel, IVS8-5T allele-specific oligonucleotide hybridization, and extensive screening of all exons.
In the CUAVD group, of 10 subjects 2 had the F508 mutation, detected using the 31 mutation panel analysis and also using the extensive CFTR screening, while 2 had the IVS8-5T variant (Table 2). Thus, for the CUAVD group, 50% of the mutations were identified by the 31 mutation panel (2/4), allele-specific oligonucleotide hybridization for IVS8-5T (2/4), and screening of all CFTR exons (2/4).
Epididymal obstruction can be caused by genitourinary surgery or infection and Young syndrome.67 Young syndrome is characterized by chronic sinopulmonary infections and epididymal obstruction.68 This condition may have an acquired origin69 and does not appear to be associated with CFTR gene mutations.26, 70 Of the 75 subjects with epididymal obstruction, 8 had a history of genitourinary surgery, 10 had a history of genitourinary infection, and 1 had a history consistent with Young syndrome. The remaining 56 men were considered to have idiopathic epididymal obstruction. None of the 19 subjects with nonidiopathic epididymal obstruction were found to have CFTR mutations using the routine panel or by gene scanning. Furthermore, the IVS8-5T allele was not detected in any of these 19 subjects. Of the 56 subjects with idiopathic epididymal obstruction, analysis using the 31 mutation panel resulted in the identification of 5 mutant alleles: F508 (2 alleles), W1282X (2 alleles), and R117H (1 allele) (Table 2). The IVS8-5T variant was found in 12 alleles. Evaluation of all CFTR exons led to the identification of 12 sequence alterations (P=.01 for comparison with the nonobstructive azoospermia group), including the same 5 mutations detected by the 31 mutation panel. Of the 7 additional mutations, G544S, 2423delG, V754M, and -741TG are associated with the CF phenotype and R258G with the CBAVD phenotype, while R75Q (identified in 2 subjects), previously thought to be a benign polymorphism, may in fact confer phenotypic features of CF.2 Therefore, of the 24 alleles with CFTR mutations in men with idiopathic epididymal obstruction, 5 (21%) were identified by routine CFTR mutation analysis, 12 (50%) by IVS8-5T allele-specific oligonucleotide analysis, and 12 (50%) by complete analysis of all CFTR exons.
In our subjects with CBAVD, CUAVD, and epididymal obstruction, an additional 46% (95% CI, 34%-58%), 50% (95% CI, 0%-100%), and 79% (95% CI, 63%-95%) of alleles with mutations or variants, respectively, would have escaped detection if assessment for IVS8-5T and an extensive screen of CFTR exons had not been performed (Table 2). It has been shown that the single most common CFTR sequence alteration in men with obstructive azoospermia is the IVS8-5T variant,13-15,24, 26-27,29, 31-34 and it is likely that most centers will routinely test for this allele. Nevertheless, even if IVS8-5T were included as part of the routine screening process, comprehensive analysis of all CFTR exons led to the identification of an additional 8 (17% [95% CI, 6%-28%]) of 47 sequence alterations in the men with CBAVD and an additional 7 (58% [95% CI, 30%-86%]) of 12 sequence alterations in those with epididymal obstruction (Table 2).
COMMENT
To date, all published reports of CFTR mutation analysis in men with obstructive azoospermia have either used a screening panel of the common CFTR gene mutations associated with the classic CF phenotype or examined all CFTR exons and immediate flanking introns. To our knowledge, the present study reports, for the first time, a comparative analysis of both methods of CFTR gene mutation testing in the same study population. We found that a substantial proportion of CFTR gene mutations in men with obstructive azoospermia consists of sequence alterations not detected by a routine panel designed for the white classic CF population.
More than 800 mutations in the CFTR gene have been reported.60 These mutations may be classified as follows: defective protein production, class 1; defective protein processing, class 2; defective channel regulation, class 3; decreased channel function, class 4; and decreased protein synthesis, class 5 mutations.2 In general, class 1, 2, or 3 mutations are expected to have more serious phenotypic consequences than class 4 or 5 mutations. The CFTR gene alterations identified in our subjects with Wolffian duct abnormalities can be divided into 4 groups. The first group consists of mutations that have been identified in classic CF patients. These severe CFTR gene mutations are associated with pancreatic insufficiency and are generally class 1 through 3 mutations: F508, W1282X, N1303K, S549R, 1677delTA, R117L, 4016insT, G544S, 2423delG, V754M, and 741TG. The second group consists of mutations found in more benign presentations of CF. These mild CFTR gene mutations are associated with pancreatic sufficiency and tend to be class 4 through 5 mutations: R117H, R334W, R347P, L206W, and P67L. The third group consists of mutations identified exclusively in some men with obstructive azoospermia; however, because these sequence alterations are extremely rare, it is only speculated that they contribute to this phenotype.7, 10, 12 These CFTR gene sequence changes include D979A, R258G, and M952T. As mentioned, D979A has been previously detected in a Vietnamese man with CBAVD,60 and interestingly, our CBAVD subject with D979A was also of Vietnamese descent. The fourth group consists of CFTR gene alterations that were formerly considered to be benign sequence variations.7, 12, 14 These include R75Q and IVS8-5T. In a substantial proportion of our patients with congenital obstructive azoospermia (36/130 [28%]), only 1 mutation or sequence alteration (including IVS8-5T) was identified. Not unexpectedly, the men with CBAVD were more likely to have 2 detectable CFTR mutations compared with those with the milder phenotype of idiopathic epididymal obstruction. Except for 1 subject who had the F508/S549R genotype, all 32 (25%) of 130 men with 2 mutant CFTR alleles carried at least 1 mild class 4 or 5 mutation.
The application of a comprehensive screen for CFTR mutations such as gene scanning (eg, multiplex heteroduplex analysis, denaturing gradient gel electrophoresis, single-strand conformation polymorphism analysis) followed by direct DNA sequencing in men with obstructive azoospermia should obviate testing for a set of common CFTR gene mutations since the former method would lead to detection of the mutations identified using such a panel and to the identification of rare or private mutations. Such a method should be more sensitive than others that directly screen for a limited number of mutations, as offered by some commercial laboratories such as Genzyme Genetics (Framingham, Mass), which tests for 70 CFTR mutations including the 31 mutations detected with the routine panel used in the present study. This 70 mutation panel would have detected no additional mutations not already identified by the 31 mutation panel in our subjects, thus emphasizing again the rarity of many of these CFTR gene mutations found in the obstructive azoospermic population. However, it must be stressed that screening for mutations in all coding regions and their immediately flanking intron sequences does not rule out mutations within the promoter region or introns of the CFTR gene. In addition, the absence of detectable sequence alterations in CFTR alleles in some subjects suggests that other genetic and/or environmental factors may contribute to the obstructive azoospermia phenotype.
The multiplex heteroduplex analysis used in the present study can detect approximately 95% of all known CFTR mutations, with a false-positive rate of about 2%.64 We estimate that the cost of this method is around US $100, which is comparable to that of a mutation panel (approximately US $50-$150 per test for 6-72 CFTR gene mutations). The estimate for the CFTR gene scanning method does not include the cost of direct DNA sequencing.
The practice of routine screening of men with obstructive azoospermia for CFTR gene mutations that are commonly associated with the classic CF phenotype may involve the erroneous assumption that the types of mutations and their frequencies in men with obstructive azoospermia are the same as those in men with classic CF. If one were to adopt the strategy of screening obstructive azoospermic men with a limited panel of CFTR gene mutations, then it would be necessary to first determine which mutations are the most common in these men. In other words, one would need to design a panel of CFTR mutations that is specific for the obstructive azoospermia phenotype. The selection of specific CFTR gene mutations for screening infertile males should be based on the same assumptions that have been used for the classic CF population, which would take into consideration the frequencies of the different mutations or variants commonly associated with the isolated obstructive azoospermia phenotype and with the ethnicity of the study population. At the present time, except for the IVS8-5T variant, it is not known with certainty which CFTR mutations constitute a significant proportion of those carried in the obstructive azoospermia population. Nevertheless, as CFTR gene mutations from larger groups of infertile men are analyzed, one could potentially develop a panel of mutations specific for the isolated obstructive azoospermia phenotype.
Another pertinent issue that warrants discussion is the screening for CFTR gene mutations in the female partners of men with obstructive azoospermia. For the couple considering assisted reproduction, we and others have advocated testing of the spouse in the situation in which her partner was found to carry at least 1 CFTR gene mutation, regardless of its class severity.55-56,71 However, since a false-negative rate exists with any mutation screening method, the spouse may wish to be tested at the same time as her partner. Of course, the spouse would also be tested as soon as possible if there were a personal or family history suggestive of CF. What is unclear at the present time is the type of screening method one should use for these women. Compounding the problem is the lack of an absolute genotype-phenotype correlation with respect to CFTR gene mutation status and the as yet uncertain consequences of inheriting at least 1 mild mutation in the offspring, male or female, produced via in vitro fertilization–intracytoplasmic sperm injection. Further complicating the picture is the increasing evidence that CFTR gene mutations may contribute etiologically to certain monosymptomatic disorders, such as isolated nasal polyposis,72 disseminated bronchiectasis,73-74 allergic bronchopulmonary aspergillosis,75 or chronic pancreatitis.76-77 Therefore, appropriate genetic counseling is required for these couples, and consideration should be given to prenatal or preimplantation diagnosis if both partners are carriers of mutant CFTR alleles, especially severe class 1 through 3 mutations. These recommendations on CFTR genotyping and genetic counseling are consistent with those outlined in the recent National Institutes of Health Consensus Statement on Genetic Testing for Cystic Fibrosis, which include offering CFTR gene mutation analysis to all couples who are considering pregnancy, regardless of infertility history.78
In summary, most laboratories screen otherwise healthy men with obstructive azoospermia for the more common mutations associated with the classic CF phenotype. However, studies performing a more exhaustive search for CFTR gene sequence alterations have demonstrated that many individuals with isolated obstructive azoospermia have rare or private mutations. Since the obstacle to conception for these men has been overcome by in vitro fertilization–intracytoplasmic sperm injection, decreasing the risk of passing pathogenic CFTR mutations on to the progeny is of paramount importance. This consequence may be avoided through clinical strategies such as genetic counseling and preimplantation or prenatal diagnosis. Further identification of mutations related to isolated obstructive azoospermia and the determination of genotype-phenotype associations may contribute to enhanced clinical management of these individuals.
AUTHOR INFORMATION
Financial Disclosures: Dr Tsui founded Ellisis, Toronto, which is primarily concerned with cloning the genes for inflammatory bowel disease. He was on the scientific advisory board of Visible Genetics Inc, Toronto, which is concerned with DNA sequencing technology. These activities are not directly related to this study. Dr Durie was a medical advisor to Scandipharm, Birmingham, Ala, which manufactures pharmaceuticals for cystic fibrosis but which does not manufacture diagnostic testing materials.
Funding/Support: This work was supported by grant DK49096-03 from the National Institutes of Health, Bethesda, Md, and grants from the Canadian Cystic Fibrosis Foundation, the Canadian Genetic Diseases Network, and the Canadian Urology Association, Toronto, Ontario.
Other Resources: The Genzyme Genetics Web site is available at: http://www.genzyme.com.
Corresponding Author and Reprints: Keith A. Jarvi, MD, FRCSC, Division of Urology, Department of Surgery, 1525-600 University Ave, Mount Sinai Hospital, Toronto, Ontario, Canada M5G 1X5 (e-mail: keith.jarvi{at}utoronto.ca).
Author Affiliations: Division of Urology, Department of Surgery, Mount Sinai Hospital (Drs Mak, Zini, and Jarvi and Mss Martin and Longley), Department of Genetics (Drs Zielenski and Tsui) and Programme in Integrative Biology (Dr Durie and Ms Martin), Research Institute, The Hospital for Sick Children; Departments of Molecular and Medical Genetics (Dr Tsui), Pediatrics (Dr Durie), Division of Urology, Department of Surgery (Drs Mak, Zini, and Jarvi), and Institute of Medical Science (Dr Jarvi), University of Toronto, Toronto, Ontario.
REFERENCES
| |
1. Welsh MJ, Tsui L-C, Boat TF, Beaudet AL. Cystic fibrosis. In: Scriver CR, Beaudet AL, Sly WS, Valle D, eds. The Metabolic and Molecular Bases of Inherited Disease New York, NY: McGraw-Hill; 1995:3799-3876.
2. Zielenski J, Tsui L-C. Cystic fibrosis: genotypic and phenotypic variations. Annu Rev Genet. 1995;29:777-807.
FULL TEXT
|
ISI
| PUBMED
3. Kaplan E, Shwachman H, Perlmutter AD, Rule A, Khaw KT, Holsclaw DS. Reproductive failure in males with cystic fibrosis. N Engl J Med. 1968;279:65-69.
ISI
| PUBMED
4. Valman HB, France NE. The vas deferens in cystic fibrosis. Lancet. 1969;2:566-567.
ISI
| PUBMED
5. Landing BH, Wells TR, Wang C-I. Abnormality of the epididymis and vas deferens in cystic fibrosis. Arch Pathol. 1969;88:569-580.
ISI
| PUBMED
6. Taussig LM, Lobeck CC, di Sant'Agnese PA, Ackerman DR, Kattwinkel J. Fertility in males with cystic fibrosis. N Engl J Med. 1972;287:586-589.
ISI
| PUBMED
7. Anguiano A, Oates RD, Amos JA, et al. Congenital bilateral absence of the vas deferens: a primarily genital form of cystic fibrosis. JAMA. 1992;267:1794-1797.
FREE FULL TEXT
8. Patrizio P, Asch RH, Handelin B, Silber SJ. Aetiology of congenital absence of vas deferens: genetic study of three generations. Hum Reprod. 1993;8:215-220.
FREE FULL TEXT
9. Osborne LR, Lynch M, Middleton PG, et al. Nasal epithelial ion transport and genetic analysis of infertile men with congenital bilateral absence of the vas deferens. Hum Mol Genet. 1993;2:1605-1609.
FREE FULL TEXT
10. Culard J-F, Desgeorges M, Costa P, et al. Analysis of the whole CFTR coding regions and splice junctions in azoospermic men with congenital bilateral aplasia of epididymis or vas deferens. Hum Genet. 1994;93:467-470.
ISI
| PUBMED
11. Oates RD, Amos JA. The genetic basis of congenital bilateral absence of the vas deferens and cystic fibrosis. J Androl. 1994;15:1-8.
FREE FULL TEXT
12. Mercier B, Verlingue C, Lissens W, et al. Is congenital bilateral absence of vas deferens a primary form of cystic fibrosis? analyses of the CFTR gene in 67 patients. Am J Hum Genet 1995;56:272-277.
ISI
| PUBMED
13. Chillon M, Casals T, Mercier B, et al. Mutations in the cystic fibrosis gene in patients with congenital absence of the vas deferens. N Engl J Med. 1995;332:1475-1480.
FREE FULL TEXT
14. Zielenski J, Patrizio P, Corey M, et al. CFTR gene variant for patients with congenital absence of vas deferens. Am J Hum Genet. 1995;57:958-960.
ISI
| PUBMED
15. Costes B, Girodon E, Ghanem N, et al. Frequent occurrence of the CFTR intron 8 (TG)n 5T allele in men with congenital bilateral absence of the vas deferens. Eur J Hum Genet. 1995;3:285-293.
ISI
| PUBMED
16. Casals T, Bassas L, Ruiz-Romero J, et al. Extensive analysis of 40 infertile patients with congenital absence of the vas deferens: in 50% of cases only one CFTR allele could be detected. Hum Genet. 1995;95:205-211.
FULL TEXT
|
ISI
| PUBMED
17. Rave-Harel N, Madgar I, Goshen R, et al. CFTR haplotype analysis reveals genetic heterogeneity in the etiology of congenital bilateral aplasia of the vas deferens. Am J Hum Genet. 1995;56:1359-1366.
ISI
| PUBMED
18. Jezequel P, Dorval I, Fergelot P, et al. Structural analysis of CFTR gene in congenital bilateral absence of vas deferens. Clin Chem. 1995;41:833-835.
FREE FULL TEXT
19. Mickle J, Milunsky A, Amos JA, Oates RD. Congenital unilateral absence of the vas deferens: a heterogeneous disorder with two distinct subpopulations based upon aetiology and mutational status of the cystic fibrosis gene. Hum Reprod. 1995;10:1728-1735.
FREE FULL TEXT
20. Durieu I, Bey-Omar F, Rollet J, et al. Diagnostic criteria for cystic fibrosis in men with congenital absence of the vas deferens. Medicine. 1995;74:42-47.
FULL TEXT
| PUBMED
21. Jarvi K, Zielenski J, Wilschanski M, et al. Cystic fibrosis transmembrane conductance regulator and obstructive azoospermia. Lancet. 1995;345:1578.
FULL TEXT
|
ISI
| PUBMED
22. Dumur V, Gervais R, Rigot JM, et al. Congenital bilateral absence of the vas deferens (CBAVD) and cystic fibrosis transmembrane regulator (CFTR): correlation between genotype and phenotype. Hum Genet. 1996;97:7-10.
FULL TEXT
|
ISI
| PUBMED
23. Bienvenu T, Hubert D, Setbon E, Dusser D, Kaplan JC, Beldjord C. A novel missense mutation in exon 16 of the cystic fibrosis transmembrane conductance regulator (CFTR) gene identified in CBAVD patients. Hum Mutat. 1996;7:182.
FULL TEXT
|
ISI
| PUBMED
24. Bienvenu T, Claustres M. Molecular basis of cystic fibrosis and congenital bilateral agenesis of vas deferens. Contracept Fertil Sex. 1996;24:495-500.
ISI
| PUBMED
25. Schlegel PN, Shin D, Goldstein M. Urogenital anomalies in men with congenital absence of the vas deferens. J Urol. 1996;155:1644-1648.
FULL TEXT
|
ISI
| PUBMED
26. Lissens W, Mercier B, Tournaye H, et al. Cystic fibrosis and infertility caused by congenital bilateral absence of the vas deferens and related clinical entities. Hum Reprod. 1996;11(suppl 4):55-78.
27. Patrizio P, Zielenski J. Congenital absence of the vas deferens: a mild form of cystic fibrosis. Mol Med Today. 1996;2:24-31.
FULL TEXT
|
ISI
| PUBMED
28. Donat R, McNeill AS, Fitzpatrick DR, Hargreave TB. The incidence of cystic fibrosis gene mutations in patients with congenital bilateral absence of the vas deferens in Scotland. Br J Urol. 1997;79:74-77.
ISI
| PUBMED
29. Bienvenu T, Adjiman M, Thiounn N, et al. Molecular diagnosis of congenital bilateral absence of the vas deferens: analyses of the CFTR gene in 64 French patients. Ann Genet. 1997;40:5-9.
ISI
| PUBMED
30. Durieu I, Bey-Omar F, Rollet J, et al. Male infertility caused by bilateral agenesis of the vas deferens: a new clinical form of cystic fibrosis? Rev Med Interne. 1997;18:114-118.
ISI
| PUBMED
31. Shin D, Gilbert F, Goldstein M, Schlegel PN. Congenital absence of the vas deferens: incomplete penetrance of cystic fibrosis gene mutations. J Urol. 1997;158:1794-1798.
FULL TEXT
|
ISI
| PUBMED
32. Dork T, Dworniczak B, Aulehla-Scholz C, et al. Distinct spectrum of CFTR gene mutations in congenital absence of vas deferens. Hum Genet. 1997;100:365-377.
FULL TEXT
|
ISI
| PUBMED
33. Kanavakis E, Tzetis M, Antoniadi T, Pistofidis G, Milligos S, Kattamis C. Cystic fibrosis mutation screening in CBAVD patients and men with obstructive azoospermia or severe oligozoospermia. Mol Hum Reprod. 1998;4:333-337.
FREE FULL TEXT
34. Mak V, Jarvi KA, Zielenski J, Durie P, Tsui L-C. Higher proportion of intact exon 9 CFTR mRNA in nasal epithelium compared with vas deferens. Hum Mol Genet. 1997;6:2099-2107.
FREE FULL TEXT
35. Temple-Smith PD, Southwick GJ, Yates CA, Trounson AO, de Krester DM. Human pregnancy by in vitro fertilization (IVF) using sperm aspirated from the epididymis. J In Vitro Fert Embryo Transf. 1985;2:119-122.
FULL TEXT
| PUBMED
36. Silber SJ, Balmaceda J, Borrero C, Ord T, Asch R. Pregnancy with sperm aspiration from the proximal head of the epididymis: a new treatment for congenital absence of the vas deferens. Fertil Steril. 1988;50:525-528.
ISI
| PUBMED
37. Patrizio P, Silber S, Ord T, Balmaceda JP, Asch RH. Two births after microsurgical sperm aspiration in congenital absence of vas deferens. Lancet. 1988;2:1364.
ISI
| PUBMED
38. Silber SJ, Ord T, Balmaceda J, Patrizio P, Asch RH. Congenital absence of the vas deferens: the fertilizing capacity of human epididymal sperm. N Engl J Med. 1990;323:1788-1792.
ABSTRACT
39. Bladou F, Grillo JM, Rossi D, et al. Epididymal sperm aspiration in conjunction with in-vitro fertilization and embryo transfer in cases of obstructive azoospermia. Hum Reprod. 1991;6:1284-1287.
FREE FULL TEXT
40. Palermo G, Joris H, Devroey P, Van Steirteghem AC. Pregnancies after intracytoplasmic injection of single spermatozoon into an oocyte. Lancet. 1992;340:17-18.
FULL TEXT
|
ISI
| PUBMED
41. Mathieu C, Guerin JF, Cognat M, Lejeune H, Pinatel MC, Lornage J. Motility and fertilizing capacity of epididymal human spermatozoa in normal and pathological cases. Fertil Steril. 1992;57:871-876.
ISI
| PUBMED
42. Oates RD, Honig S, Berger MJ, Harris D. Microscopic epididymal sperm aspiration (MESA): a new option for treatment of the obstructive azoospermia associated with cystic fibrosis. J Assist Reprod Genet. 1992;9:36-40.
FULL TEXT
|
ISI
| PUBMED
43. Van Steirteghem AC, Nagy Z, Joris H, et al. High fertilization and implantation rates after intracytoplasmic sperm injection. Hum Reprod. 1993;8:1061-1066.
FREE FULL TEXT
44. Fukugaki H, Suganuma N, Kitagawa T, et al. Successful in vitro fertilization and pregnancy by micromanipulation with epididymal sperm. J Assist Reprod Genet. 1994;11:452-458.
FULL TEXT
|
ISI
| PUBMED
45. Harari O, Bourne H, McDonald M, et al. Intracytoplasmic sperm injection: a major advance in the management of severe male subfertility. Fertil Steril. 1995;64:360-368.
ISI
| PUBMED
46. Schlegel PN, Palermo GD, Alikani M, et al. Micropuncture retrieval of epididymal sperm with in vitro fertilization: importance of in vitro micromanipulation techniques. Urology. 1995;46:238-241.
FULL TEXT
|
ISI
| PUBMED
47. Son IP, Hong JY, Lee YS, et al. Efficacy of microsurgical epididymal sperm aspiration (MESA) and intracytoplasmic sperm injection (ICSI) in obstructive azoospermia. J Assist Reprod Genet. 1996;13:69-72.
FULL TEXT
|
ISI
| PUBMED
48. Madgar I, Seidman DS, Levran D, et al. Micromanipulation improves in-vitro fertilization results after epididymal or testicular sperm aspiration in patients with congenital absence of the vas deferens. Hum Reprod. 1996;11:2151-2154.
FREE FULL TEXT
49. Cha KY, Oum KB, Kim HJ. Approaches for obtaining sperm in patients with male factor infertility. Fertil Steril. 1997;67:985-995.
FULL TEXT
|
ISI
| PUBMED
50. Mansour RT, Kamal A, Fahmy I, Tawab N, Serour GI, Aboulghar MA. Intracytoplasmic sperm injection in obstructive and non-obstructive azoospermia. Hum Reprod. 1997;12:1974-1979.
FREE FULL TEXT
51. Handyside AH, Lesko JG, Tarin JJ, Winston RM, Hughes MR. Birth of a normal girl after in vitro fertilization and preimplantation diagnostic testing for cystic fibrosis. N Engl J Med. 1992;327:905-909.
ABSTRACT
52. de Kretser DM. The potential of intracytoplasmic sperm injection (ICSI) to transmit genetic defects causing male infertility. Reprod Fertil Dev. 1995;7:137-141.
FULL TEXT
| PUBMED
53. Cummins JM, Jequier AM. Concerns and recommendations for intracytoplasmic sperm injection (ICSI) treatment. Hum Reprod. 1995;10(suppl 1):138-143.
54. Mak V, Jarvi KA. The genetics of male infertility. J Urol. 1996;156:1245-1256.
FULL TEXT
|
ISI
| PUBMED
55. Johnson MD. Genetic risks of intracytoplasmic sperm injection in the treatment of male infertility: recommendations for genetic counseling and screening. Fertil Steril. 1998;70:397-411.
FULL TEXT
|
ISI
| PUBMED
56. Lawler AM, Gearhart JD. Genetic counseling for patients who will be undergoing treatment with assisted reproductive technology. Fertil Steril. 1998;70:412-413.
FULL TEXT
|
ISI
| PUBMED
57. Jarvi K, McCallum S, Zielenski J, et al. Heterogeneity of reproductive tract abnormalities in men with absence of the vas deferens: role of cystic fibrosis transmembrane conductance regulator gene mutations. Fertil Steril. 1998;70:724-728.
FULL TEXT
|
ISI
| PUBMED
58. Census Operations Division. Statistics Canada, 1996 Census Nation: Tables. Ottawa, Ontario: Census Operations Division; 1996.
59. Miller SA, Dykes DD, Polesky HF. A simple salting out procedure for extracting DNA from human nucleated cells. Nucleic Acids Res. 1988;16:1215.
FREE FULL TEXT
60. Cystic Fibrosis Genetic Analysis Consortium Website. Available at: http://www.genet.sickkids.on.ca/cftr/. Accessed May 12, 1999.
61. Mullis K, Faloona F, Scharf S, Saiki R, Horn G, Erlich H. Specific enzymatic amplification of DNA in vitro: the polymerase chain reaction. Cold Spring Harb Symp Quant Biol. 1986;51(pt 1):263-273.
62. Zielenski J, Rozmahel R, Bozon D, et al. Genomic DNA sequence of the cystic fibrosis transmembrane conductance regulator (CFTR) gene. Genomics. 1991;10:214-228.
FULL TEXT
|
ISI
| PUBMED
63. Kiesewetter S, Macek M Jr, Davis C, et al. A mutation in CFTR produces different phenotypes depending on chromosomal background. Nat Genet. 1993;5:274-278.
FULL TEXT
|
ISI
| PUBMED
64. Aznarez I, Onay T, Tzounzouris J, et al. An efficient protocol for CFTR mutation detection based on multiplex heteroduplex analysis (mHET) [abstract]. Pediatr Pulmonol. 1998;17(suppl):332.
65. Cuppens H, Teng H, Raeymaekers P, De Boeck C, Cassiman JJ. CFTR haplotype backgrounds on normal and mutant CFTR genes. Hum Mol Genet. 1994;3:607-614.
FREE FULL TEXT
66. Dork T, Fislage R, Neumann T, Wulf B, Tummler B. Exon 9 of the CFTR gene: splice site haplotypes and cystic fibrosis mutations. Hum Genet. 1994;93:67-73.
ISI
| PUBMED
67. Schoysman R. Epididymal causes of male infertility: pathogenesis and management. Int J Androl. 1982;5(suppl):120-134.
68. Young D. Surgical treatment of male infertility. J Reprod Fertil. 1970;23:541-542.
PUBMED
69. Hendry WF, A'Hern RP, Cole PJ. Was Young's syndrome caused by exposure to mercury in childhood? BMJ. 1993;307:1579-1582.
FREE FULL TEXT
70. Friedman KJ, Teichtahl H, De Kretser DM, et al. Screening Young syndrome patients for CFTR mutations. Am J Respir Crit Care Med. 1995;152:1353-1357.
ABSTRACT
71. Meschede D, Horst J, Williams C, Williamson R. Genetic testing and counselling for congenital bilateral absence of the vas deferens. Lancet. 1994;343:1566-1567.
ISI
| PUBMED
72. Burger J, Macek M Jr, Stuhrmann M, Reis A, Krawczak M, Schmidtke J. Genetic influences in the formation of nasal polyps. Lancet. 1991;337:974.
PUBMED
73. Pignatti PF, Bombieri C, Marigo C, Benetazzo M, Luisetti M. Increased incidence of cystic fibrosis gene mutations in adults with disseminated bronchiectasis. Hum Mol Genet. 1995;4:635-639.
FREE FULL TEXT
74. Pignatti PF, Bombieri C, Benetazzo M, et al. CFTR gene variant IVS8-5T in disseminated bronchiectasis. Am J Hum Genet. 1996;58:889-892.
ISI
| PUBMED
75. Miller PW, Hamosh A, Macek M Jr, et al. Cystic fibrosis transmembrane conductance regulator (CFTR) gene mutations in allergic bronchopulmonary aspergillosis. Am J Hum Genet. 1996;59:45-51.
ISI
| PUBMED
76. Sharer N, Schwarz M, Malone G, et al. Mutations of the cystic fibrosis gene in patients with chronic pancreatitis. N Engl J Med. 1998;339:645-652.
FREE FULL TEXT
77. Cohn JA, Friedman KJ, Noone PG, Knowles MR, Silverman LM, Jowell PS. Relation between mutations of the cystic fibrosis gene and idiopathic pancreatitis. N Engl J Med. 1998;339:653-658.
FREE FULL TEXT
78. National Institutes of Health Consensus Statement. Genetic testing for cystic fibrosis. Available at: http://odp.od.nih.gov/consensus/cons/106/106_statement.htm. Accessed May 12, 1999.
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