Mutations in the cystic fibrosis gene in patients with congenital absence of the vas deferens

IVS8-5T Allele of CFTR is the Risk Factor in Chronic Pancreatitis, Especially in Idiopathic Chronic Pancreatitis

BACKGROUND

Cystic fibrosis transmembrane conductance regulator IVS8-5T gene variation appears to be associated with a higher risk of chronic pancreatitis (CP); however, there is inconsistency between previous reported studies. Here, we performed a meta-analysis to investigate this relationship.

MATERIALS AND METHODS

PubMed and WANFANG databases were searched for the case-control studies that contained Patients with CP with IVS8-5T variation. Odd ratios (ORs) and 95% confidence intervals (CIs) were calculated to assess the relevance of IVS8-5T gene variation and CP.

RESULTS

Analysis showed that the frequency of the 5T allele was significantly higher in CP subjects than that in control subjects (OR = 1.43, 95% CI: 1.13-1.81, I² = 1.2%). Based on the subgroup analysis stratified by etiology, the 5T allele was associated with a higher risk of idiopathic chronic pancreatitis (ICP) (OR = 1.80, 95% CI: 1.18-2.76, I² = 0.0%) and not alcoholic CP (OR = 2.14, 95% CI: 0.98-4.66, I² = 0.0%). Further study indicated that the 5T allele was related to higher ICP prevalence in the European population (OR = 1.79, 95% CI: 1.06-3.03, I² = 0.0%). In contrast, there was no significant difference between ICP subjects and healthy controls within the Asian population (OR = 1.84, 95% CI: 0.91-3.72, I² = 38.0%).

CONCLUSIONS

Cystic fibrosis transmembrane conductance regulator IVS8-5T is a risk factor in patients with CP. IVS8-5T variation may play a significant role in the occurrence of ICP, especially in the European population.

The true panel of cystic fibrosis mutations in the Sicilian population

Background

The aim was to establish the true risk of having an affected child with Cystic Fibrosis (CF) in the Sicilian infertile population.

Methods

A longitudinal CFTR screening of 1279 Sicilian infertile patients for all CFTR mutations sequencing the entire gene by Next Generation Sequencing (NGS) was performed from patient’s blood.

Results

One patient out of 16 was a carrier of a CFTR mutation. Twenty-four mutations were found. Theoretically one couple out of 256 was at risk of CF transmission.

Conclusions

The risk of CF transmission is unexpectedly high in Sicily and with a high heterogeneity. Sequencing an entire and long gene such as CFTR makes accessible the true panel of mutations in a specific population and helps better to understand the true risk of having an affected child.

First custom next-generation sequencing infertility panel in Latin America: design and first results

Objective

To present the development of the first custom gene panel for the diagnosis of male and female infertility in Latin America.

Methods

We developed a next-generation sequencing (NGS) panel that assesses genes associated with infertility. The panel targeted exons and their flanking regions. Selected introns in the CFTR gene were also included. The FMR1 gene and Y chromosome microdeletions were analyzed with other recommended methodologies. An in-house developed bioinformatic pipeline was applied for the interpretation of the results. Clear infertility phenotypes, idiopathic infertility, and samples with known pathogenic variants were evaluated.

Results

A total of 75 genes were selected based on female (primary ovarian insufficiency, risk of ovarian hyperstimulation syndrome, recurrent pregnancy loss, oocyte maturation defects, and embryo development arrest) and male conditions (azoospermia, severe oligospermia, asthenozoospermia, and teratozoospermia). The panel designed was used to assess 25 DNA samples. Two of the variants found were classified as pathogenic and enable the diagnosis of a woman with secondary amenorrhea and a man with oligoasthenoteratozoospermia. Targeted NGS assay metrics resulted in a mean of 180X coverage, with more than 98% of the bases covered ≥20X.

Conclusion

Our custom gene sequencing panel designed for the diagnosis of male and female infertility caused by genetic defects revealed the underlying genetic cause of some cases of infertility. The panel will allow us to develop more precise approaches in assisted reproduction.

What Role Does CFTR Play in Development, Differentiation, Regeneration and Cancer?

One of the key features associated with the substantial increase in life expectancy for individuals with CF is an elevated predisposition to cancer, firmly established by recent studies involving large cohorts. With the recent advances in cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapies and the increased long-term survival rate of individuals with cystic fibrosis (CF), this is a novel challenge emerging at the forefront of this disease. However, the mechanisms linking dysfunctional CFTR to carcinogenesis have yet to be unravelled. Clues to this challenging open question emerge from key findings in an increasing number of studies showing that CFTR plays a role in fundamental cellular processes such as foetal development, epithelial differentiation/polarization, and regeneration, as well as in epithelial–mesenchymal transition (EMT). Here, we provide state-of-the-art descriptions on the moonlight roles of CFTR in these processes, highlighting how they can contribute to novel therapeutic strategies. However, such roles are still largely unknown, so we need rapid progress in the elucidation of the underlying mechanisms to find the answers and thus tailor the most appropriate therapeutic approaches.

Splice modulating antisense oligonucleotides restore some acid-alpha-glucosidase activity in cells derived from patients with late-onset Pompe disease

Pompe disease is caused by mutations in the GAA gene, resulting in deficient lysosomal acid-α-glucosidase activity in patients, and a progressive decline in mobility and respiratory function. Enzyme replacement therapy is one therapeutic option, but since not all patients respond to this treatment, alternative interventions should be considered. One GAA mutation, c.-32-13T > G, impacts upon normal exon 2 splicing and is found in two-thirds of late-onset cases. We and others have explored a therapeutic strategy using splice modulating phosphorodiamidate morpholino oligomers to enhance GAA exon 2 inclusion in the mature mRNA of patients with one c.-32-13T > G allele. We designed 20 oligomers and treated fibroblasts derived from five patients to identify an oligomer sequence that maximally increased enzyme activity in all fibroblasts. The most effective splice correcting oligomer was chosen to treat forced-myogenic cells, derived from fibroblasts from nine patients carrying the c.-32-13T > G mutation. After transfection, we show increased levels of the full-length GAA transcript, acid-α-glucosidase protein, and enzyme activity in all patients’ myogenic cells, regardless of the nature of the mutation in the other allele. This data encourages the initiation of clinical trials to assess the therapeutic efficacy of this oligomer for those patients carrying the c.-32-13T > G mutation.

A novel hemizygous loss-of-function mutation in ADGRG2 causes male infertility with congenital bilateral absence of the vas deferens

PURPOSE

Cystic fibrosis transmembrane conductance regulator (CFTR) and adhesion G protein-coupled receptor G2 (ADGRG2) have been identified as the main pathogenic genes in congenital bilateral absence of the vas deferens (CBAVD), which is an important cause of obstructive azoospermia. This study aimed to identify the disease-causing gene in two brothers with CBAVD from a Chinese consanguineous family and reveal the intracytoplasmic sperm injection (ICSI) outcomes in these patients.

METHODS

Whole-exome sequencing and Sanger sequencing were used to identify the candidate pathogenic genes. Real-time polymerase chain reaction, immunohistochemistry, and immunofluorescence were used to assess the expression of the mutant gene. Moreover, the ICSI results from both patients were retrospectively reviewed.

RESULTS

A novel hemizygous loss-of-function mutation (c.G118T: p.Glu40*) in ADGRG2 was identified in both patients with CBAVD. This mutation is absent from the human genome databases and causes an early translational termination in the third exon of ADGRG2. Expression analyses showed that both the ADGRG2 mRNA and the corresponding protein were undetectable in the proximal epididymal tissue of ADGRG2-mutated patients. ADGRG2 expression was restricted to the apical membranes of non-ciliated epithelia in human efferent ducts, which was consistent with a previous report in mice. Both ADGRG2-mutated patients had normal spermatogenesis and had successful clinical outcomes following ICSI.

CONCLUSIONS

Our study verifies the pathogenic role of ADGRG2 in X-linked CBAVD and broadens the spectrum of ADGRG2 mutations. In addition, we found positive ICSI outcomes in the two ADGRG2-mutated CBAVD patients.

Congenital unilateral absence of vas deferens with contralateral testicular atrophy

We present a case report of a 25-year-old obese man complaining of primary infertility for 2 years. After a thorough examination and investigation were done, he had congenital unilateral absence of vas deferens with ipsilateral renal agenesis and a palpable vas deferens in the contralateral side with testicular atrophy. Semen analysis showed low semen volume (0.5 mL) with azoospermia. Hence, a scrotal exploration and a crossover transseptal vasoepididymostomy to relocate the vas deferens were done. After 6 months, the sperm concentration reached 5 × 10⁶/mL with good motility (40%) and volume (1.5 mL).

Genetic diagnosis and sperm retrieval outcomes for Chinese patients with congenital bilateral absence of vas deferens

BACKGROUND

Congenital bilateral absence of the vas deferens (CBAVD) is a frequent cause of obstructive azoospermia. CBAVD is mainly caused by mutations in the CFTR (cystic fibrosis transmembrane conductance regulator) gene and is also related to the X-linked ADGRG2 (adhesion G protein-coupled receptor G2) gene. Genetic screening and counseling strategies for Chinese CBAVD populations remain controversial because the genetic background of CBAVD in Chinese population is largely unknown.

OBJECTIVES

In this study, we aimed to study the mutation spectrum of CFTR and ADGRG2 in a group of CBAVD patients and to evaluate sperm retrieval outcomes in a subset of CBAVD patients.

MATERIALS AND METHODS

Next-generation targeted sequencing was used to identify mutations in the CFTR and ADGRG2 genes in 38 CBAVD patients. In addition, we followed and analyzed nine of the 38 patients who were undergoing sperm retrieval surgery.

RESULTS

In total, 27 of 38 (71.05%) patients carried at least one likely pathogenic or pathogenic mutation in CFTR or ADGRG2. In addition to the IVS9-5T allele, 15 CFTR and 1 ADGRG2 mutations were identified, including 4 novel mutations. CFTR hot-spot mutations were not identified in our study. Spermatozoon was successfully obtained in all nine patients who underwent MESA or TESE surgery, but most patients had spermatozoa with relatively low motility and high abnormality rates.

DISCUSSION AND CONCLUSION

Except for the IVS9-5T allele, hot-spot mutations of CFTR may not exist in Chinese CBAVD patients. Therefore, next-generation targeted sequencing for whole CFTR and ADGRG2 gene may be the appropriate genetic testing method, and genetic counseling may be different from Caucasian populations. We observed a high success rate of sperm retrieval with relatively low motility and high abnormality rates in Chinese CBAVD patients. However, this is only a weak conclusion due to the small sample size.

Genetics of the congenital absence of the vas deferens

Congenital absence of the vas deferens (CAVD) may have various clinical presentations depending on whether it is bilateral (CBAVD) or unilateral (CUAVD), complete or partial, and associated or not with other abnormalities of the male urogenital tract. CBAVD is usually discovered in adult men either during the systematic assessment of cystic fibrosis or other CFTR-related conditions, or during the exploration of isolated infertility with obstructive azoospermia. The prevalence of CAVDs in men is reported to be approximately 0.1%. However, this figure is probably underestimated, because unilateral forms of CAVD in asymptomatic fertile men are not usually diagnosed. The diagnosis of CAVDs is based on clinical, ultrasound, and sperm examinations. The majority of subjects with CAVD carry at least one cystic fibrosis-causing mutation that warrants CFTR testing and in case of a positive result, genetic counseling prior to conception. Approximately 2% of the cases of CAVD are hemizygous for a loss-of-function mutation in the ADGRG2 gene that may cause a familial form of X-linked infertility. However, despite this recent finding, 10–20% of CBAVDs and 60–70% of CUAVDs remain without a genetic diagnosis. An important proportion of these unexplained CAVDs coexist with a solitary kidney suggesting an early organogenesis disorder (Wolffian duct), unlike CAVDs related to CFTR or ADGRG2 mutations, which might be the result of progressive degeneration that begins later in fetal life and probably continues after birth. How the dysfunction of CFTR, ADGRG2, or other genes such as SLC29A3 leads to this involution is the subject of various pathophysiological hypotheses that are discussed in this review.

Regulation of CFTR Biogenesis by the Proteostatic Network and Pharmacological Modulators

Cystic fibrosis (CF) is the most common lethal inherited disease among Caucasians in North America and a significant portion of Europe. The disease arises from one of many mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator, or CFTR. The most common disease-associated allele, F508del, along with several other mutations affect the folding, transport, and stability of CFTR as it transits from the endoplasmic reticulum (ER) to the plasma membrane, where it functions primarily as a chloride channel. Early data demonstrated that F508del CFTR is selected for ER associated degradation (ERAD), a pathway in which misfolded proteins are recognized by ER-associated molecular chaperones, ubiquitinated, and delivered to the proteasome for degradation. Later studies showed that F508del CFTR that is rescued from ERAD and folds can alternatively be selected for enhanced endocytosis and lysosomal degradation. A number of other disease-causing mutations in CFTR also undergo these events. Fortunately, pharmacological modulators of CFTR biogenesis can repair CFTR, permitting its folding, escape from ERAD, and function at the cell surface. In this article, we review the many cellular checkpoints that monitor CFTR biogenesis, discuss the emergence of effective treatments for CF, and highlight future areas of research on the proteostatic control of CFTR.

Cystic fibrosis carriers are at increased risk for a wide range of cystic fibrosis-related conditions

Cystic fibrosis (CF) carriers are at increased risk for most of the conditions that commonly occur in people with CF. Given that there are more than 10 million CF carriers in the United States alone, the morbidity attributable to the CF carrier state is likely substantial. Thus, identifying CF carriers may aid in the prevention, diagnosis, and treatment of several common and uncommon disorders.

Autosomal recessive diseases, such as cystic fibrosis (CF), require inheritance of 2 mutated genes. However, some studies indicate that CF carriers are at increased risk for some conditions associated with CF. These investigations focused on single conditions and included small numbers of subjects. Our goal was to determine whether CF carriers are at increased risk for a range of CF-related conditions. Using the Truven Health MarketScan Commercial Claims database (2001–2017), we performed a population-based retrospective matched-cohort study. We identified 19,802 CF carriers and matched each carrier with 5 controls. The prevalence of 59 CF-related diagnostic conditions was evaluated in each cohort. Odds ratios for each condition were computed for CF carriers relative to controls. All 59 CF-related conditions were more prevalent among carriers compared with controls, with significantly increased risk (P < 0.05) for 57 conditions. Risk was increased for some conditions previously linked to CF carriers (e.g., pancreatitis, male infertility, bronchiectasis), as well as some conditions not previously reported (e.g., diabetes, constipation, cholelithiasis, short stature, failure to thrive). We compared our results with 23,557 subjects with CF, who were also matched with controls; as the relative odds of a given condition increased among subjects with CF, so did the corresponding relative odds for carriers (P < 0.001). Although individual-level risk remained low for most conditions, because there are more than 10 million carriers in the US, population-level morbidity attributable to the CF carrier state is likely substantial. Genetic testing may inform prevention, diagnosis, and treatment for a broad range of CF carrier-related conditions.

Universal strategy for preimplantation genetic testing for cystic fibrosis based on next-generation sequencing

PURPOSE

We developed and applied a universal strategy for preimplantation genetic testing for all cystic fibrosis gene mutations (PGT-CF) based on next-generation sequencing (NGS).

METHODS

A molecular protocol was designed to diagnose all CF mutations at preimplantation stage. The detection of CF mutations was performed by direct gene sequencing and linkage strategy testing 38 specific SNPs located upstream and inside the gene for PGT-CF. Seventeen couples at risk of CF transmission decided to undergo PGT-CF. Trophectoderm cell biopsies were performed on days 5-6 blastocysts. PGT for aneuploidy (PGT-A) was performed from the same samples. Tested embryos were transferred on further natural cycles.

RESULTS

PGT was performed on 109 embryos. Fifteen CF mutations were tested. PGT-CF and PGT-A were conclusive for, respectively, 92.7% and 95.3% of the samples. A mean of 24.1 SNPs was informative per couple. After single embryo transfer on natural cycle, 81.3% of the transferred tested embryos implanted.

CONCLUSIONS

The present protocol based on the entire CFTR gene sequencing together with informative SNPs outside and inside the gene can be applied to diagnose all CF mutations at preimplantation stage.

Prevention of cystic fibrosis: The beginning of the end?

Prenatal and postnatal treatment with a CFTR modifier attenuates pathological changes in a ferret model of cystic fibrosis (Sun et al., this issue).

Universal strategy for preimplantation genetic testing for cystic fibrosis based on next generation sequencing

Purpose

We developed and applied a universal strategy for preimplantation genetic testing for all cystic fibrosis gene mutations (PGT-CF) based on next-generation sequencing (NGS).

Methods

A molecular protocol was designed to diagnose all CF mutations at preimplantation stage. The detection of CF mutations was performed by direct gene sequencing and linkage strategy testing 38 specific SNPs located upstream and inside the gene for PGT-CF. Seventeen couples at risk of CF transmission decided to undergo PGT-CF. Trophectoderm cell biopsies were performed on day 5–6 blastocysts. PGT for aneuploidy (PGT-A) was performed from the same samples. Tested embryos were transferred on further natural cycles.

Results

PGT was performed on 109 embryos. Fifteen CF mutations were tested. PGT-CF and PGT-A were conclusive for respectively 92.7% and 95.3% of the samples. A mean of 24.1 SNPs was informative per couple. After a single embryo transfer on natural cycle, 81.3% of the transferred tested embryos were implanted.

Conclusions

The present protocol based on the entire CFTR gene together with informative SNPs outside and inside the gene can be applied to diagnose all CF mutations at preimplantation stage.

Electronic supplementary material

The online version of this article (10.1007/s10815-019-01635-2) contains supplementary material, which is available to authorized users.

A rare frameshift variant in trans with the IVS9-5T allele of CFTR in a Chinese pedigree with congenital aplasia of vas deferens

PURPOSE

Congenital aplasia of vas deferens (CAVD) is an atypical form of cystic fibrosis (CF) and causes obstructive azoospermia and male infertility. Compound heterozygous variants of CFTR are the main cause of CAVD. However, most evidence comes from genetic screening of sporadic cases and little is from pedigree analysis. In this study, we performed analysis in a Chinese pedigree with two CAVD patients in order to determine the genetic cause of this familial disorder.

METHODS

In the present study, we performed whole-exome sequencing and co-segregation analysis in a Chinese pedigree involving two patients diagnosed with CAVD.

RESULTS

We identified a rare frameshift variant (NM_000492.3: c.50dupT;p.S18Qfs*27) and a frequent CBAVD-causing variant (IVS9-TG13-5T) in both patients. The frameshift variant introduced a premature termination codon and was not found in any public databases or reported in the literature. Co-segregation analysis confirmed these two variants were in compound heterozygous state. The other male members, who harbored the frameshift variant and benign IVS9-7T allele, did not have any typical clinical manifestations of CF or CAVD.

CONCLUSION

Our findings may broaden the mutation spectrum of CFTR in CAVD patients and provide more familial evidence that the combination of a mild variant and a severe variant in trans of CFTR can cause vas deferens malformation.

Where are we going with gene screening for male infertility?

Male infertility is a heterogenous disease process requiring the proper functioning and interaction of thousands of genes. Given the number of genes involved, it is thought that genetic causes contribute to most cases of infertility. Identifying these causes, however, is challenging. Infertility is associated with negative health outcomes, such as cancer, highlighting the need to further understand the genetic underpinnings of this condition. This paper describes the genetic and genomic tests currently available to identify the etiology of male infertility and then will discuss emerging technologies that may facilitate diagnosis and treatment of in the future.

A novel mutation (-195C>A) in the promoter region of CFTR gene is associated with Chinese Congenital Bilateral Absence of Vas Deferens (CBAVD)

Congenital bilateral absence of vas deferens (CBAVD), a frequent cause of obstructive azoospermia and male infertility in Chinese, is mainly due to mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. This study aim to explore the promoter region of CFTR gene in CBAVD patients and study the mutations by functional analysis, and to discuss the significance of mutation testing in this area. We performed screening analysis on 65 CBAVD patients and 50 controls to detect mutations in the CFTR gene, and studied the functions of promoter mutations using reporter gene constructs, transient transfection techniques and subsequent assessment of transcriptional activity and expression levels. Mutations c.-195C>A and c.-34C>T in the promoter region of the CFTR gene were detected in 4 of our Chinese CBAVD patients, one of which was novel (c.-195C>A) and located in the conservative area, as well as the binding site of SP1 transcription factor through the prediction of bioinformatics analysis. By reverse transcription qPCR assay and luciferase assay, we validated it as a functional disease-causing variant that down-regulates the CFTR gene expression, and this effect was related to the amount of transcription factors. This study was the first to explore the promoter region of the CFTR gene in Chinese, and we believe that mutations in this region are associated with Chinese CBAVD patients. We also suggest a systematic strategy for genotyping Chinese CBAVD couples, which should help in developing reproductive counseling.

Genetic defects in human azoospermia

As with many other diseases, genetic testing in human azoospermia was initially restricted to karyotype analyses (leading to diagnostic chromosome rearrangement tests for Klinefelter and other syndromes). With the advent of molecular biology in the 1980s, genetic screening was broadened to analyses of Y chromosome microdeletions and the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR). Decades later, the emergence of whole-genome techniques has led to the identification of other genetic defects associated with human azoospermia. Although TEX11 and ADGRG2 defects are frequently described in men with azoospermia, most of the causal gene defects found to date are private (i.e. identified in a small number of consanguineous families).

Here, we provide an up-to-date overview of all the types of genetic defects known to be linked to human azoospermia and try to give clinical practice guidelines according to azoospermia phenotype. Along with homozygous mutations, polymorphisms and epigenetic defects are also briefly discussed. However, as these variations predispose to azoospermia, a specific review will be needed to compile data on all the particular genetic variations reported in the literature.

The role of SLC9A3 in Taiwanese patients with congenital bilateral absence of vas deferens (CBAVD)

Congenital bilateral absence of vas deferens (CBAVD) is a special entity in obstructive azoospermia. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene are involved in Taiwanese CBAVD but most heterozygous 5T variant. The solute carrier family 9 isoform 3 (SLC9A3) is the Na+/H+ exchanger, which interacts with CFTR and regulates the Ca2+ homeostasis. Loss of SLC9A3 decreases CFTR protein and causes obstructive azoospermia in mice. It also causes mal-reabsorption by the efferent tubules, which leads to the obstructive phenomenon and eventually results in testicular atrophy. In 6-month old SLC9A3 deficiency mice, the atrophy of their vas deferens and seminal vesicles become more prominent. Decreases of CFTR expression in the reproductive organ in the SLC9A3 deficient (-/-) mice prove the interaction between CFTR and SLC9A3 in the reproductive tract. Most of Taiwanese CBAVD have at least one variant of SLC9A3 deletion and CFTR IVS8-5T, which co-contribute to Taiwanese CBAVD. The report indicates SLC9A3 deficiency can reverse the pathological changes in the gastrointestinal tract of CF mice. Further research can explore the definite mechanism of SLC9A3 and its role interacting with CFTR in different organ systems, which can contribute to novel treatment for the patients with cystic fibrosis and CBAVD.

Investigation of multi-trait associations using pathway-based analysis of GWAS summary statistics

Background

Genome-wide association studies (GWAS) have been successful in identifying disease-associated genetic variants. Recently, an increasing number of GWAS summary statistics have been made available to the research community, providing extensive repositories for studies of human complex diseases. In particular, cross-trait associations at the genetic level can be beneficial from large-scale GWAS summary statistics by using genetic variants that are associated with multiple traits. However, direct assessment of cross-trait associations using susceptibility loci has been challenging due to the complex genetic architectures in most diseases, calling for advantageous methods that could integrate functional interpretation and imply biological mechanisms.

Results

We developed an analytical framework for systematic integration of cross-trait associations. It incorporates two different approaches to detect enriched pathways and requires only summary statistics. We demonstrated the framework using 25 traits belonging to four phenotype groups. Our results revealed an average of 54 significantly associated pathways (ranged between 18 and 175) per trait. We further proved that pathway-based analysis provided increased power to estimate cross-trait associations compared to gene-level analysis. Based on Fisher’s Exact Test (FET), we identified a total of 24 (53) pairs of trait-trait association at adjusted p_FET < 1 × 10^− 3 (p_FET < 0.01) among the 25 traits. Our trait-trait association network revealed not only many relationships among the traits within the same group but also novel relationships among traits from different groups, which warrants further investigation in future.

Conclusions

Our study revealed that risk variants for 25 different traits aggregated in particular biological pathways and that these pathways were frequently shared among traits. Our results confirmed known mechanisms and also suggested several novel insights into the etiology of multi-traits.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5373-7) contains supplementary material, which is available to authorized users.

Evaluation of the azoospermic male: a committee opinion

The purpose of this document is to review the current methods of diagnosis and evaluation for men with azoospermia.

Clinical and genetic characteristics of cystic fibrosis in CHINESE patients: a systemic review of reported cases

Cystic fibrosis (CF) is a rare disease most commonly seen in Caucasians. Only a few Chinese CF patients have been described in literature, taking into account the large population of China. In this systematic review, we collected the clinical and genetic information of 71 Chinese CF patients based on all available data. Compared with Caucasians, Chinese CF patients often present atypical symptoms, mainly displaying symptoms of pulmonary infection with fewer digestive symptoms. An ethnicity-specific CFTR variant spectrum was also observed in CF patients of Chinese origin, with p.Gly970Asp as the most common mutation while p.Phe508del, the most common pathogenic mutation in CF patients of Caucasian origin, is rare, suggesting the necessity of a Chinese-specific CFTR variant screening panel. Besides, multiplex ligation-dependent probe amplification analysis should be routinely considered, especially for those with unidentified mutations. Potential under-diagnosis of CF in Chinese patients might be caused by a combination of atypical clinical features and genetic heterogeneity in Chinese CF patients, the inaccessibility of sweat and genetic testing facilities, and the one-child policy in China. With the approval of promising small molecule correctors and potentiators, molecular characterization of Chinese-specific CFTR mutations will help to realize more precise treatment for Chinese CF patients.

Update on the cellular and molecular aspects of cystic fibrosis transmembrane conductance regulator (CFTR) and male fertility

CFTR protein regulates electrolyte and fluid transport in almost all tissues with exocrine function, including male reproductive tract. Mutation of CFTR gene causes cystic fibrosis (CF), which affects the function of several organs, and impairs male fertility. The role of CFTR protein in different compartments of male reproductive tract (testis, epididymis, sperm) as well as an impact of CFTR mutation(s) on male fertility phenotype is discussed in relation with the choice of optimal technique for Assisted Reproductive Techniques (ART) management.

Compound heterozygous mutations in CFTR causing CBAVD in Chinese pedigrees

BACKGROUND

Congenital bilateral absence of the vas deferens (CBAVD) is an important cause of obstructive azoospermia and male infertility. Mutations of CFTR caused the majority of CBAVD cases, and ADGRG2 was recently identified as a new pathogenic gene. Yet, most of the genetic evidence came from sporadic cases, and only one mutation in CFTR can be found in patients.

METHODS

In present study, we collected two CBAVD pedigrees, each having two affected male siblings. We performed whole exome sequencing on all patients and validated all potential variants by Sanger sequencing.

RESULTS

We excluded ADGRG2 variants but identified compound heterozygous variants of CFTR in both families (NM_000492.3:c.1210-33_1210-6GT[13]T[5] and c.4056G>C;p.Gln1352Cys in pedigree 1, c.592G>C;p.Ala198Pro and c.3717G>A;p.Arg1239= in pedigree 2), which were subsequently validated by direct sequencing. c.1210-33_1210-6GT[13]T[5] (also known as IVS8-T5-TG13) was a known disease-causing variant causing the skipping of exon 9 of CFTR and inherited from the proband's mother. p.Gln1352Cys and Ala198Pro were rare or novel in public databases and predicted to be deleterious. The p.Arg1239= was a synonymous variant but located at the end of an exon, which was predicted to alter the splicing pattern.

CONCLUSION

Our study, in which compound heterozygous variants were identified in two pedigrees, provides more familial evidence that only recessive variants (homozygous or compound heterozygous) in CFTR cause CBAVD. Furthermore, whole exome sequencing may be utilized as a useful tool for mutation screening of genes causing CBAVD.

X-linked ADGRG2 mutation and obstructive azoospermia in a large Pakistani family

We performed whole exome sequencing to identify an unknown genetic cause of azoospermia and male infertility in a large Pakistani family. Three infertile males were subjected to semen analysis, hormone testing, testicular histology, ultrasonography, karyotyping, Y-chromosome microdeletion and CFTR testing. The clinical testing suggested a diagnosis of obstructive azoospermia (OA). To identify the cause, we performed whole exome sequencing (WES) for 2 infertile brothers and 2 fertile family members. For segregation analysis and variant confirmation, we performed Sanger sequencing. WES data analysis of the family revealed segregated variants in 3 candidate genes. We considered novel nonsense variant c.2440C > T(p.Arg814*) in X-linked gene ADGRG2 as biologically most plausible. It is predicted to truncate the protein by 204 amino acids (aa) at a key transmembrane domain. Adgrg2-knockout male mice show sperm loss due to obstructive fluid stasis, while ADGRG2 mutations cause OA in the infertile male patients. Our analysis of testicular histology reveals secondary severe reduction of spermatogenesis, consistent with human and knockout mouse phenotypes. The ADGRG2 nonsense mutation is absent in the largest population databases, ExAC and gnomAD. Analysis of the novel nonsense mutation in extended family members confirmed co-segregation of the mutation with OA in all affected males. The likely pathogenic nature of the mutation is supported by its truncation effect on the transmembrane domain and distinctive ultrasound results. The study demonstrates effectiveness of WES in discovering a genetic cause of azoospermia.

Description of rare mutations and a novel variant in Brazilian patients with Cystic Fibrosis: a case series from a referral center in the Bahia State

Knowledge of the genetic profile of Cystic Fibrosis (CF) contributes to a better understanding of the genotype/phenotype relationship, particularly in mixed populations such as in Brazil. To describe clinical data of CF patients with rare or not yet observed CFTR gene mutations in Brazil. It was a case series of CF patients followed-up at a referral center. Clinical and laboratory data were obtained through medical records. Molecular analysis of the mutations was performed by conventional methods and/or by next-generation sequencing. Ten patients were studied, seven had five pathogenic mutations without previous description in Brazil (Q1100P, Y109C, A107P, E1409K and K162E), one of which has not yet been reported in patients with CF (A107P). Among the seven patients, three (two siblings) had the second mutant allele of rare occurrence among Brazilians patients (G1069R and 2307insA). Three other patients also had at least one rare variant (V201M, S466X and G1069R). The age of the CF diagnosis ranged from 1 to 190 months in the ten cases and the main clinical manifestations were respiratory symptoms and difficulty in gaining weight. All but one patient presented clinical and/or laboratory data compatible with pancreatic insufficiency. The identification of rare or not yet described CFTR mutations in patients with CF in Brazil highlights the high genetic heterogeneity in this population. Knowledge of the genotypic profile of Brazilian CF patients can contribute to the development of specific mutation panels for the genetic investigation targeting each region of the country, as well as helping to understand the complex genotype/phenotype relationship, especially in mixed populations.

CFTR variants and renal abnormalities in males with congenital unilateral absence of the vas deferens (CUAVD): a systematic review and meta-analysis of observational studies

PURPOSE

CFTR variant is the main genetic contributor to congenital (unilateral/bilateral) absence of the vas deferens (CAVD/CUAVD/CBAVD). We performed a systematic review to elucidate the genetic link between CFTR variants, CUAVD, and the associated risk of renal abnormality (RA).

METHODS

We searched relevant databases for eligible articles reporting CFTR variants in CUAVD. The frequency of CFTR variants and RA, and the odds ratios (ORs) for common alleles and RA risk, were pooled under random-/fixed-effect models. Subgroup analyses and heterogeneity tests were performed.

RESULTS

Twenty-three studies were included. Among CUAVD patients, 46% had at least one CFTR variant, with 27% having one and 5% having two. The allele frequency in CUAVD was 4% for F508del and 9% for 5T. The summary OR for 5T risk in CUAVD was 5.79 compared with normal controls and 2.82 compared with non-CAVD infertile males. The overall incidence of RA was 22% in CUAVD. The pooled OR for RA risk among CUAVD patients was 4.85 compared with CBAVD patients.

CONCLUSION

CFTR variants are common in CUAVD, and the 5T allele may be associated with increased CUAVD risk. CUAVD patients bear a higher RA risk than CBAVD patients, but this is not associated with CFTR variants.

The Delta F508 Mutation in Cystic Fibrosis and Impact on Sinus Development

Background

Cystic fibrosis (CF) patients often have widespread inflammatory paranasal sinus disease with an increased incidence of frontal, maxillary, and sphenoid hypoplasia. The most common genetic defect in CF is the delta F508 mutation. The effect of specific CF genotypes on phenotypic sinus development and infections is not well understood. The purpose of this study was to determine whether the homozygous delta F508 mutation is associated with an increased incidence of sinus hypoplasia when compared with other mutations.

Methods

This study is a retrospective review of all adult patients seen at our CF center from 1996 to 2005. Patients ≥18 years old with a CF diagnosis using genetic and sweat chloride testing and sinus CT scans were included. Frontal sinus aplasia/hypoplasia and maxillary and sphenoid sinus hypoplasia were documented using published criteria. Data collected included patient demographics, genetic mutations, and prior sinus surgeries.

Results

Forty-five patients were identified with an average age of 32 years (range, 18–48 years). Thirty-one patients had prior sinus surgeries. Delta F508 homozygotes (n = 25) had a significantly increased frequency of underdeveloped frontal (98%), maxillary (70%), and sphenoid (100%) sinuses (p < 0.001) when compared with other mutations (69, 8, and 50%, respectively).

Conclusion

CF patients homozygous for the delta F508 mutation have a greater incidence of hypoplastic or underdeveloped sinuses. Whether this is secondary to an increased frequency of sinus infections or a phenotypic expression of the genetic mutation itself remains an area for further investigation.

Comorbidity of the congenital absence of the vas deferens

Congenital absence of the vas deferens (CAVD) is a relatively rare anomaly that may contribute to male infertility. The aim of this study was to evaluate the clinical features of patients with CAVD and to emphasise some pathological conditions that may be detected during the infertility work-up or follow-up of these patients. The charts of 150 males with the diagnosis of CAVD were evaluated retrospectively. The demographic characteristics, reasons for attendance, the way of diagnosis, interventions for infertility before and after attendance, physical examination findings, reproductive hormone levels, semen analysis results, genetical analysis results and resultant live birth events were all included in the study. There were 101 bilateral and 43 unilateral CAVD cases. Thirty-two males (30.2%) had some renal abnormalities. Two cases, one with bilateral and one with unilateral agenesis, died because of colon cancer at a young age. One case with CUAVD had acute lymphoblastic leukaemia. Congenital absence of the vas deferens should not be seen only as a fertility problem because of the many genotypic or phenotypic disorders that may be present with it. These disorders can cause serious general health problems either presently or in future and can also be transmitted to future generations.

Next-generation sequencing for patients with non-obstructive azoospermia: implications for significant roles of monogenic/oligogenic mutations

Azoospermia affects up to 1% of adult men. Non-obstructive azoospermia is a multifactorial disorder whose molecular basis remains largely unknown. To date, mutations in several genes and multiple submicroscopic copy-number variations (CNVs) have been identified in patients with non-obstructive azoospermia. The aim of this study was to clarify the contribution of nucleotide substitutions in known causative genes and submicroscopic CNVs in the genome to the development of non-obstructive azoospermia. To this end, we conducted sequence analysis of 25 known disease-associated genes using next-generation sequencing and genome-wide copy-number analysis using array-based comparative genomic hybridization. We studied 40 Japanese patients with idiopathic non-obstructive azoospermia. Functional significance of molecular alterations was assessed by in silico analyses. As a result, we identified four putative pathogenic mutations, four rare polymorphisms possibly associated with disease risk, and four probable neutral variants in 10 patients. These sequence alterations included a heterozygous splice site mutation in SOHLH1 and a hemizygous missense substitution in TEX11, which have been reported as causes of non-obstructive azoospermia. Copy-number analysis detected five X chromosomal or autosomal CNVs of unknown clinical significance, in addition to one known pathogenic Y chromosomal microduplication. Five patients carried multiple molecular alterations. The results indicate that monogenic and oligogenic mutations, including those in SOHLH1 and TEX11, account for more than 10% of cases of idiopathic non-obstructive azoospermia. Furthermore, this study suggests possible contributions of substitutions in various genes as well as submicroscopic CNVs on the X chromosome and autosomes to non-obstructive azoospermia, which require further validation.

Congenital bilateral absence of the vas deferens as an atypical form of cystic fibrosis: reproductive implications and genetic counseling

Congenital bilateral absence of the vas deferens (CBAVD) is found in 1% to 2% of males with infertility and is present in 6% of obstructive azoospermia cases. Nearly 95% of men with cystic fibrosis (CF, an autosomal recessive disorder) have CBAVD. There are genetic links between CBAVD and CF. Some mutations in the gene encoding cystic fibrosis transmembrane conductance regulator (CFTR) can lead to CBAVD as a monosymptomatic form of CF. With the use of assisted reproductive techniques (ART), especially testicular or epididymal sperm aspiration, intracytoplasmic sperm injection, and in vitro fertilization, it is possible that men with CBAVD can produce offspring. Therefore, genetic counseling should be offered to couples undergoing ART to discuss the probability of having offspring that carry CFTR gene mutations. The aim of this review was to present the main cause of CBAVD, to call attention to its implications for assisted reproduction, and to show the importance of genetic counseling for couples where men have CBAVD, as they can have offspring with a lethal disease.

Autosomal single-gene disorders involved in human infertility

Human infertility, defined as the inability to conceive after 1 year of unprotected intercourse, is a healthcare problem that has a worldwide impact. Genetic causes of human infertility are manifold. In addition to the chromosomal aneuploidies and rearrangements, single-gene defects can interfere with human fertility. This paper provides a review of the most common autosomal recessive and autosomal dominant single-gene disorders involved in human infertility. The genes reviewed are CFTR, SPATA16, AURKC, CATSPER1, GNRHR, MTHFR, SYCP3, SOX9, WT1 and NR5A1 genes. These genes may be expressed throughout the hypothalamic-pituitary–gonadal-outflow tract axis, and the phenotype of affected individuals varies considerably from varying degrees of spermatogenic dysfunction leading to various degrees of reduced sperm parameters, through hypogonadotropic hypogonadism reslting in pubertal deficiencies, until gonadal dysgenesis and XY and XX sex reversal. Furthermore, congenital bilateral absence of the vas deferens, as well as premature ovarian failure, have been reported to be associated with some single-gene defects.

The suppression of premature termination codons and the repair of splicing mutations in CFTR

Premature termination codons (PTC) originate from nucleotide substitution introducing an in-frame PTC. They induce truncated, usually non-functional, proteins, degradation of the PTC containing transcripts by the nonsense-mediated decay (NMD) pathway and abnormal exon skipping. Readthrough compounds facilitate near cognate amino-acyl-tRNA incorporation, leading potentially to restoration of a functional full-length protein. Splicing mutations can lead to aberrantly spliced transcripts by creating a cryptic splice site or destroying a normal site. Most mutations result in disruption of the open reading frame and activation of NMD. Antisense oligonucleotides are single stranded short synthetic RNA-like molecules chemically modified to improve their stability and ability to recognize their target RNAs and modify the splice site. This review focuses on recent developments in therapies aiming to improve the health of CF patients carrying nonsense or splicing mutations.

A missense mutation in SLC26A3 is associated with human male subfertility and impaired activation of CFTR

Chloride absorption and bicarbonate excretion through exchange by the solute carrier family 26 member 3 (SLC26A3) and cystic fibrosis transmembrane conductance regulator (CFTR) are crucial for many tissues including sperm and epithelia of the male reproductive tract. Homozygous SLC26A3 mutations cause congenital chloride diarrhea with male subfertility, while homozygous CFTR mutations cause cystic fibrosis with male infertility. Some homozygous or heterozygous CFTR mutations only manifest as male infertility. Accordingly, we studied the influence of SLC26A3 on idiopathic infertility by sequencing exons of SLC26A3 in 283 infertile and 211 control men. A heterozygous mutation c.2062 G > C (p.Asp688His) appeared in nine (3.2%) infertile men, and additionally, in two (0.9%) control men, whose samples revealed a sperm motility defect. The p.Asp688His mutation is localized in the CFTR-interacting STAS domain of SLC26A3 and enriched in Finland, showing a significant association with male infertility in comparison with 6,572 Finnish (P < 0.05) and over 120,000 global alleles (P < 0.0001) (ExAC database). Functional studies showed that while SLC26A3 is a strong activator of CFTR-dependent anion transport, SLC26A3-p.Asp688His mutant retains normal Cl⁻/HCO₃⁻ exchange activity but suppresses CFTR, despite unaffected domain binding and expression. These results suggest a novel mechanism for human male infertility─impaired anion transport by the coupled SLC26A3 and CFTR.

Pathogenic role of ADGRG2 in CBAVD patients replicated in Chinese population

Congenital bilateral absence of the vas deferens (CBAVD) is an important cause of obstructive azoospermia and male infertility worldwide. Cystic fibrosis transmembrane conductance regulator (CFTR) mutations are the main pathogenic cause, although a proportion of cases are still unexplained. Recently, adhesion G protein-coupled receptor G2 (ADGRG2) gene, a novel pathogenic gene for CBAVD was identified. We did a single population replication study in Chinese CBAVD patients to replicate its role in CBAVD developing. In this study, we performed whole-exome sequencing in 18 unrelated CBAVD patients and identified two missense variants in two patients (c.G1709A, p.C570Y; and c.A2968G, p.K990E). Both variants were predicted to be deleterious and highly conserved in silico. The p.C570Y variant is located in the G protein-coupled receptor (GPCR) proteolysis site domain, which is functionally necessary for autoproteolysis, while the p.K990E variant is in the N-terminal fragment that may regulate activity of the adhesion GPCR. We did not find any potential pathogenic CFTR variants, implying the ADGRG2 variants are the genetic cause in these patients. To the best of our knowledge, these are the first two ADGRG2 variants to be identified in Chinese CBAVD patients, which further validate the disease-causing role of ADGRG2 in this congenital defect.

The CFTR gene mild variants poly-T, TG repeats and M470V detection in Indian men with congenital bilateral absence of vas deferens

The aim of the study was to detect the frequency of the CFTR gene variants poly-T, TG repeats and c.1408A>G p.Met470Val (M470V) in Indian men with congenital bilateral absence of the vas deferens (CBAVD). Men diagnosed with CBAVD (n = 76), their female partners (n = 76) and healthy men from general population (n = 50) were recruited. Genomic DNA was isolated and the polymorphic regions of IVS9- c.1210-12T [5] and M470V were amplified using specific primers followed by Sanger's DNA sequencing. A statistically significant increase in the frequency of heterozygous IVS9- c.1210-12T [5] (39.4%) was observed in CBAVD men as compared to controls (14%). The allelic distribution of c.1210-12T [5], c.1210-12T [7] and c.1210-12T [9] in CBAVD men was 21%, 64.4% and 13% and that in healthy controls was 7%, 73% and 20% respectively. Longest TG repeat c.1210-34TG [13] was found in association with c.1210-12T [5] with an allelic frequency of 5.9% in CBAVD men. We found a significant association of c.1210-34TG [12]/c.1210-34TG [13] - c.1210-12[5] -V470 allele in CBAVD men. Twelve female partners harboured a heterozygous c.1210-12T [5] allele. The study emphasises the need to screen both partners for the polymorphisms M470V, poly-T, TG tract repeats in addition to population-specific known CFTR gene mutations.

CFTR gene mutations and polymorphism are associated with non-obstructive azoospermia: From case-control study

A variety of experimental studies have yielded evidence that the cystic fibrosis transmembrane conductance regulator (CFTR) protein participates in the process of spermatogenesis. However, the association between CFTR gene and non-obstructive azoospermia (NOA) disease remained to be a question. First, we reviewed available data from the PubMed and Embase databases before May 2016 to find the most common mutations of CFTR gene in NOA patients. Second, an original case-control study was conducted on NOA patients (n=100) and a control group consisting of fertile males (n=100), selected from August 2015 to March 2017, to detect CFTR gene mutations and polymorphism. Peripheral blood samples from NOA patients and normal controls were analyzed for the presence of specific sequences of CFTR gene by polymerase chain reaction amplification followed by direct sequencing. From our comprehensive review, 12 case-control studies were found concerning the relation between CFTR gene mutations and polymorphism and NOA disease. Fifty-four mutations were mentioned and IVS8 poly-T, TG repeats, F508del and R117H mutations were the most common ones. Based on that, we detected IVS8 poly-T, TG repeats, F508del, R117H and M470V mutations in our case control study. We found that the T5 allele was present at a significantly higher rate in NOA patients than in the control group (5.00% versus 0.00%, p<0.01) with increased risk having NOA [Odds ratios (OR) 2.05, 95% confidence intervals (CI) 1.85-2.27]. The T5 variant was always accompanied by TG12 (10/10) and V470 allele participated in most TG12T5 haplotypes (8/10). TG12T5-V470 haplotype also enhanced risk of having NOA [OR 2.04, 95% CI 1.84-2.26]. F508del and R117H mutations were not found in either group. In conclusion, the polyvariant mutant genes of CFTR: T5 allele and TG12-T5-V470 genotype are correlated with NOA, but F508del and R117H mutations have low possibility to be associated with NOA.

Loss of SLC9A3 decreases CFTR protein and causes obstructed azoospermia in mice

Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene cause cystic fibrosis (CF) and are associated with congenital bilateral absence of the vas deferens (CBAVD), which is the major cause of infertility in male patients with CF. However, most Taiwanese patients with CBAVD do not carry major CFTR mutations. Some patients have a single copy deletion of the solute carrier family 9 isoform 3 (SLC9A3) gene. SLC9A3 is a Na⁺/H⁺ exchanger, and depleted Slc9a3 in male mice causes infertility due to the abnormal dilated lumen of the rete testis and efferent ductules. Furthermore, SLC9A3 interacts with CFTR in the pancreatic duct and functions as a genetic modifier of CF. However, SLC9A3 function and its relation to CFTR expression in the male reproductive tract in vivo remain elusive. In the present study, we found that CFTR expression was dramatically decreased in the epididymis and vas deferens of Slc9a3 knockout mice. Adult Slc9a3^-/- mice showed not only significantly decreased epididymis and vas deferens weight but also increased testis weight. Furthermore, Slc9a3^-/- mice developed obstructive azoospermia because of abnormal abundant secretions and calcification in the lumen of the reproductive tract. Ultrastructural analysis of the epithelium in Slc9a3^–/–epididymis and vas deferens displayed disorganized and reduced number of stereocilia and numerous secretory apparatuses. Our data revealed that interdependence between SLC9A3 and CFTR is critical for maintaining a precise microenvironment in the epithelial cytoarchitecture of the male reproductive tract. The Slc9a3-deficient mice with impaired male excurrent ducts in this study provide proof for our clinical findings that some Taiwanese of CBAVD carry SLC9A3 deletion but without major CFTR mutations.

Cystic fibrosis (CF) is the most common inherited life-threatening disease in Caucasians. The most well-known cause of CF is a genetic defect in CFTR, an apical membrane chloride and bicarbonate channel. The symptoms of CF include defects in the respiratory, digestive, and male reproductive systems. Most male patients with CF are infertile due to congenital bilateral absence of the vas deferens (CBAVD), which leads to obstructive azoospermia. Nevertheless, Taiwanese patients with CBAVD do not carry the common mutations of CFTR found in Caucasians. We have identified a potential candidate, SLC9A3, of which a single copy is lost in Taiwanese patients with CBAVD. In addition to the previously reported role of SLC9A3 in the digestive system and efferent ductules, we now report that the SLC9A3 deficiency causes obstructive azoospermia and impairs the epithelial structure of the reproductive tract. Loss of SLC9A3 also leads to dramatic reduced expression of CFTR in the reproductive tract. We suggest that the interplay between SLC9A3 and CFTR is responsible for CF-related infertility. Thus, we have characterized a potential critical player in the pathogenesis of CBAVD and provide a new diagnostic candidate for Asian patients with CBAVD.

Diagnosis of Cystic Fibrosis in Nonscreened Populations

OBJECTIVE

Although the majority of cases of cystic fibrosis (CF) are now diagnosed through newborn screening, there is still a need to standardize the diagnostic criteria for those diagnosed outside of the neonatal period. This is because newborn screening started relatively recently, it is not performed everywhere, and even for individuals who were screened, there is the possibility of a false negative. To limit irreversible organ pathology, a timely diagnosis of CF and institution of CF therapies can greatly benefit these patients.

STUDY DESIGN

Experts on CF diagnosis were convened at the 2015 CF Foundation Diagnosis Consensus Conference. The participants reviewed and discussed published works and instructive cases of CF diagnosis in individuals presenting with signs, symptoms, or a family history of CF. Through a modified Delphi methodology, several consensus statements were agreed upon. These consensus statements were updates of prior CF diagnosis conferences and recommendations.

RESULTS

CF diagnosis in individuals outside of newborn screening relies on the clinical evidence and on evidence of CF transmembrane conductance regulator (CFTR) dysfunction. Clinical evidence can include typical organ pathologies seen in CF such as bronchiectasis or pancreatic insufficiency but often represent a broad range of severity including mild cases. CFTR dysfunction can be demonstrated using sweat chloride testing, CFTR molecular genetic analysis, or CFTR physiologic tests. On the basis of the large number of patients with bona fide CF currently followed in registries with sweat chloride levels between 30 and 40 mmol/L, the threshold considered "intermediate" was lowered from 40 mmol/L in the prior diagnostic guidelines to 30 mmol/L. The CF diagnosis was also discussed in the context of CFTR-related disorders in which CFTR dysfunction may be present, but the individual does not meet criteria for CF.

CONCLUSIONS

CF diagnosis remains a rare but important condition that can be diagnosed when characteristic clinical features are seen in an individual with demonstrated CFTR dysfunction.