Cystic fibrosis screening: a fetus with hyperechogenic bowel may be the index case

Prenatal Ultrasound Suspicion of Cystic Fibrosis in a Multiethnic Population: Is Extensive CFTR Genotyping Needed?

In families without a Cystic Fibrosis (CF) history, fetal ultrasound bowel abnormalities can unexpectedly reveal the disease. Isolated or in association, the signs can be fetal bowel hyperechogenicity, intestinal loop dilatation and non-visualization of fetal gallbladder. In these cases, search for CF transmembrane conductance regulator (CFTR) gene mutations is part of the recommended diagnostic practices, with a search for frequent mutations according to ethnicity, and, in case of the triad of signs, with an exhaustive study of the gene. However, the molecular diagnosis remains a challenge in populations without well-known frequent pathogenic variants. We present a multiethnic cohort of 108 pregnancies with fetal bowel abnormalities in which the parents benefited from an exhaustive study of the CFTR gene. We describe the new homozygous p.Cys1410* mutation in a fetus of African origin. We did not observe the most frequent p.Phe508del mutation in our cohort but evidenced variants undetected by our frequent mutations kit. Thanks to the progress of sequencing techniques and despite the difficulties of interpretation occasionally encountered, we discuss the need to carry out a comprehensive CFTR study in all patients in case of fetal bowel abnormalities.

Incidence and Carrier Frequency of CFTR Gene Mutations in Pregnancies With Echogenic Bowel in Nova Scotia and Prince Edward Island

OBJECTIVE

Fetal echogenic bowel (echogenic bowel) is associated with cystic fibrosis (CF), with a reported incidence ranging from 1% to 13%. Prenatal testing for CF in the setting of echogenic bowel can be done by screening parental or fetal samples for pathogenic CFTR variants. If only one pathogenic variant is identified, sequencing of the CFTR gene can be undertaken, to identify a second pathogenic variant not covered in the standard screening panel. Full gene sequencing, however, also introduces the potential to identify variants of uncertain significance (VUSs) that can create counselling challenges and cause parental anxiety. To provide accurate counselling for families in the study population, the incidence of CF associated with echogenic bowel and the carrier frequency of CFTR variants were investigated.

METHODS

All pregnancies for which CF testing was undertaken for the indication of echogenic bowel (from Nova Scotia and Prince Edward Island) were identified (January 2007-July 2017). The CFTR screening and sequencing results were reviewed, and fetal outcomes related to CF were assessed.

RESULTS

A total of 463 pregnancies with echogenic bowel were tested. Four were confirmed to be affected with CF, giving an incidence of 0.9% in this cohort. The carrier frequency of CF among all parents in the cohort was 5.0% (1 in 20); however, when excluding parents of affected fetuses, the carrier frequency for the population was estimated at 4.1% (1 in 25). CFTR gene sequencing identified an additional VUS in two samples.

CONCLUSION

The incidence of CF in pregnancies with echogenic bowel in Nova Scotia and Prince Edward Island is 0.9%, with an estimated population carrier frequency of 4.1%. These results provide the basis for improved counselling to assess the risk of CF in the pregnancy, after parental carrier screening, using Bayesian probability. Counselling regarding VUSs should be undertaken before gene sequencing.

Prediction, prevention and personalisation of medication for the prenatal period: genetic prenatal tests for both rare and common diseases

Genetic testing usually helps physicians to determine possible genetic diseases in unborn babies, genetic disorders of patients and the carriers who might pass the mutant gene on to their children. They are performed on blood, tissues or other body fluids. In recent years, the screening tests and diagnostic tests have improved quickly and, as a result, the risks of pregnancy can be determined more commonly and physicians can diagnose several genetic disorders in the prenatal period. Detecting the abnormalities in utero enables correct management of the pregnancy, prenatal and postnatal medical care, and it is also important for making well informed decisions about continuing or terminating a pregnancy. Besides the improvements of conventional invasive diagnostic tests, the discovery of circulating cell-free foetal nucleic acids in maternal plasma has developed a new point of view for non-invasive prenatal diagnosis recently.

Hyperechogenic fetal bowel: an ultrasonographic marker for adverse fetal and neonatal outcome?

"Soft markers" are considered variants of normal and should be considered distinct from fetal anatomic malformations. Hyperechogenicity of the fetal bowel, is one of the few soft markers that can also associated with a variety of other pathologic conditions. In this review we will focalise our attention on the significate of an increased echogenicity of fetal bowel and on management of fetuses with this condition.

Focus on cystic fibrosis and other disorders evidenced in fetuses with sonographic finding of echogenic bowel: 16-year report from Brittany, France

OBJECTIVE

Pregnancies medical follow-up and ultrasonography development have enabled detection of fetal echogenic bowel, a sign associated with various pathologies, including cystic fibrosis. Based on the long experience of a region where cystic fibrosis is frequent (Brittany, France), we describe disorders diagnosed in fetal echogenic bowel fetuses and assess ultrasonography ability in detecting cystic fibrosis in utero.

STUDY DESIGN

We reviewed the cases of fetal echogenic bowel diagnosed in pregnant women living in Brittany and referred for CFTR gene analysis over the 1992-2007 period (n = 289).

RESULTS

A disorder was diagnosed in 32.2% of the fetuses, cystic fibrosis being the most commonly identified (7.6%). We also found digestive malformations (7.0%), chromosomal abnormalities (3.7%), and maternofetal infections (3.7%). Combining these data with our ongoing newborn screening program since 1989 showed that ultrasonography enabled diagnosis of 10.7% of the cystic fibrosis cases.

CONCLUSION

This study highlights the importance of pregnancy ultrasound examinations and their efficiency in detecting cystic fibrosis.

Notable contribution of large CFTR gene rearrangements to the diagnosis of cystic fibrosis in fetuses with bowel anomalies

Grade III fetal bowel hyperechogenicity and/or loop dilatation observed at the second trimester of pregnancy can be due to several disease conditions, including cystic fibrosis (CF). Screening for frequent CF mutations is performed as a first step and, in certain situations, such as when a frequent CF mutation is found in the fetus, the increased risk of CF justifies an in-depth study of the second allele. To determine the contribution of large CFTR gene rearrangements in such cases, detected using a semiquantitative fluorescent multiplex PCR (QFM-PCR) assay, we collated data on 669 referrals related to suspicion of CF in fetuses from 1998 to 2009. Deletions were found in 5/70 cases in which QFM-PCR was applied, dele19, dele22_23, dele2_6b, dele14b_15 and dele6a_6b, of which the last three remain undescribed. In 3/5 cases, hyperechogenicity was associated with dilatation and/or gallbladder anomalies. Of the total cases of CF recognized in the subgroup of first-hand referrals, deletions represent 16.7% of CF alleles. Our study thus strengthens the need to consider large CFTR gene rearrangements in the diagnosis strategy of fetal bowel anomalies, in particular in the presence of multiple anomalies.

Best practice guidelines for molecular genetic diagnosis of cystic fibrosis and CFTR-related disorders--updated European recommendations

The increasing number of laboratories offering molecular genetic analysis of the CFTR gene and the growing use of commercial kits strengthen the need for an update of previous best practice guidelines (published in 2000). The importance of organizing regional or national laboratory networks, to provide both primary and comprehensive CFTR mutation screening, is stressed. Current guidelines focus on strategies for dealing with increasingly complex situations of CFTR testing. Diagnostic flow charts now include testing in CFTR-related disorders and in fetal bowel anomalies. Emphasis is also placed on the need to consider ethnic or geographic origins of patients and individuals, on basic principles of risk calculation and on the importance of providing accurate laboratory reports. Finally, classification of CFTR mutations is reviewed, with regard to their relevance to pathogenicity and to genetic counselling.

Best practice guidelines for molecular genetic diagnosis of cystic fibrosis and CFTR-related disorders--updated European recommendations

The increasing number of laboratories offering molecular genetic analysis of the CFTR gene and the growing use of commercial kits strengthen the need for an update of previous best practice guidelines (published in 2000). The importance of organizing regional or national laboratory networks, to provide both primary and comprehensive CFTR mutation screening, is stressed. Current guidelines focus on strategies for dealing with increasingly complex situations of CFTR testing. Diagnostic flow charts now include testing in CFTR-related disorders and in fetal bowel anomalies. Emphasis is also placed on the need to consider ethnic or geographic origins of patients and individuals, on basic principles of risk calculation and on the importance of providing accurate laboratory reports. Finally, classification of CFTR mutations is reviewed, with regard to their relevance to pathogenicity and to genetic counselling.

Hyperechogenic fetal bowel: counseling difficulties

The detection of echodense fetal bowel on ultrasound examination in the second trimester of pregnancy justifies invasive procedures such as amniocentesis to detect an underlying cause. We present a case in which initial tests identified only one mutation in the cystic fibrosis transmembrane regulator (CFTR)-gene of the fetus, the family history being negative for CF. Strongly reduced intestinal enzyme activities suggested intestinal obstruction and further increased the estimated risk for CF. After the 24th gestational week, a second mutation was found, confirming cystic fibrosis in this child. Problems in counseling in this particular case are discussed.

Mid-trimester hyperechogenic bowel in a fetus of Japanese origin carrying a new mutation of CFTR gene (L548Q)

We present a case of a fetus with hyperechogenic bowel, in which the L548Q mutation was detected in the mother of Japanese origin and the deltaF508 mutation in the father of Caucasian origin. The fetus proved to be compound heterozygous. Research into cystic fibrosis transmembrane conductance regulator (CFTR) mutations in this case was triggered by the fact that the fetus had a characteristic hyperechogenic bowel image with normal karyotype and no indications of intrauterine infections. Hyperechogenic bowel is highly indicative of a CFTR gene mutation. The incidence of cystic fibrosis (CF) in fetuses with mid-trimester hyperechogenic bowel is 5%, but once the most frequent mutations have been accounted for, rarer mutations must be investigated.

Controversial ultrasound findings

This article has reviewed a few of the more controversial findings in the field of obstetric ultrasound. For each one evidence-based strategies for the management of affected pregnancies have been suggested, derived from what the authors believe is the best information available. In some cases, this information is very limited, which can make counseling these patients extremely difficult. Some physicians find using specific likelihood ratios helpful in these complex discussions. An example of the relative likelihood ratios for several markers of trisomy 21 is illustrated in Table 10. Although the management of each of the findings discussed in this article is different, a few generalizations can be made. To begin with, the detection of any abnormal finding on ultrasound should prompt an immediate detailed ultrasound evaluation of the fetus by someone experienced in the diagnosis of fetal anomalies. If there is more than one abnormal finding on ultrasound, if the patient is over the age of 35, or if the multiple marker screen is abnormal, an amniocentesis to rule out aneuploidy should be recommended. Of the six ultrasound findings reviewed here, the authors believe that only echogenic bowel as an isolated finding confers a high enough risk of aneuploidy to recommend an amniocentesis in a low-risk patient. The other findings in isolation in a low-risk patient seem to confer only a modest increased risk of aneuploidy, if any, and this risk is certainly less than the risk of unintended loss from amniocentesis. Wherever possible, modifiers of this risk, such as maternal age, history, and first and second multiple marker screening, should be used to define more clearly the true risk of aneuploidy. As obstetric ultrasound moves forward, particularly into the uncharted waters of clinical use of three- and four-dimensional ultrasound, one can expect a whole new crop of ultrasound findings with uncertain clinical significance. Clinicians are well advised to await well-designed studies to determine the clinical significance of these findings before altering clinical care.

Hyperechogenic fetal bowel: a large French collaborative study of 682 cases

Hyperechogenic fetal bowel is detected in 0.1-1.8% of pregnancies during the second or third trimester. This ultrasound sign is associated with cystic fibrosis or other conditions (e.g., chromosomal anomalies, viral infection) but no large-scale prospective studies have been conducted. This 1997-1998 multicenter study in 22 molecular biology laboratories identified 682 cases of hyperechogenic fetal bowel detected by routine ultrasound examination during the second (86%) or third trimester. The fetal bowel was considered hyperechogenic when its echogenicity was broadly similar to, or greater than, that of the surrounding bone. Karyotyping, screening for viral infection, and screening for cystic fibrosis mutations were performed in all cases. Pregnancy outcome and postnatal follow-up were obtained in 656 of the 682 cases (91%). In 447 cases (65.5%), a normal birth was observed. Multiple malformations were observed in 47 cases (6.9%), a significant chromosomal anomaly was noted in 24 (3.5%), cystic fibrosis in 20 (3%), and viral infection in 19 (2.8%). In utero unexplained fetal death occurred in 1.9% of cases, toxemia in 1.2%, IUGR in 4.1%, and premature birth in 6.2%. This study demonstrates that this ultrasound sign is potentially associated with medically significant outcomes. Having established that the bowel is hyperechogenic, recommended investigations should include a detailed scan with Doppler measurements, fetal karyotyping, cystic fibrosis screening, and infectious disease screening. After birth, newborns require pediatric examination because a surgical treatment may be necessary. This should be combined with clear counseling of the parents.

Prenatal diagnosis for paediatricians

In Ontario, approximately 140,000 women deliver newborn infants each year. Of these women, 60,000 to 70,000 have multiple marker screening, 10,000 undergo amniocentesis or chorion villus sampling and virtually all have at least one prenatal ultrasound. Multiple marker screening is not used in every province and territory; however, amniocentesis and prenatal ultrasound are used throughout Canada. Most paediatric patients will have been exposed to some form of prenatal diagnosis. If an abnormality is found prenatally, parents may have concerns to discuss with the paediatrician after the child is born. Likewise, if a child with a problem is born following a normal pregnancy, the parents will want to know why the problem was missed prenatally. Paediatricians should be aware of prenatal tests that have been performed to understand better their patients and their families.

Predicting the risk of cystic fibrosis with abnormal ultrasound signs of fetal bowel: results of a French molecular collaborative study based on 641 prospective cases

Hyperechogenic fetal bowel is prenatally detected by ultrasound during the second trimester of pregnancy in 0.1-1.8% of fetuses. It has been described as a normal variant but has often been associated with severe diseases, notably cystic fibrosis (CF). The aim of our study was to determine the risk of CF in a prospective study of 641 fetuses with ultrasonographically abnormal fetal bowel and the residual risk when only one mutation is detected in the fetus. Fetal cells and/or parental blood cells were screened for CFTR mutations. Two screening steps were used, the first covering the mutations most frequently observed in French CF patients (mutation detection rate of 70-90%) and, when a CF mutation was detected, a DGGE-sequencing strategy. We observed a 3.1% risk of CF when a digestive tract anomaly was prenatally observed at routine ultrasound examination. The risk was higher when hyperechogenicity was associated with bowel dilatation (5/29; 17%) or with the absence of gall bladder (2/8; 25%). The residual risk of CF was 11% when only one CF mutation was detected by the first screening step, thereby justifying in-depth screening. Mutations associated with severe CF (DeltaF508 mutation) were more frequently observed in these ultrasonographically and prenatally detected CF cases. However, the frequency of heterozygous cases was that observed in the normal population, which demonstrates that heterozygous carriers of CF mutations are not at increased risk for hyperechogenic bowel. In conclusion, fetal bowel anomalies indicate a risk of severe cystic fibrosis and justify careful CFTR molecular analysis.

Hyperechogenic fetal bowel and Down syndrome. Results of a French collaborative study based on 680 prospective cases

Hyperechogenic fetal bowel is prenatally detected by ultrasound during the second trimester of pregnancy in 0.1% to 1.8% of foetuses. It has been described as a normal variant and has often been associated with severe diseases, notably Down syndrome. The aim of the present study was to determine the risk of trisomy 21 in a prospective study of 680 fetuses with hyperechogenic foetal bowel. Karyotyping was performed on amniotic cells in 632 cases, and outcome was known in 655 cases. A 2.5% risk of Down syndrome and a 1% risk of other severe chromosomal anomalies were observed. Hyperechogenicity was isolated in 11/17 Down syndrome cases, and associated with other ultrasound anomalies in all seven cases of severe chromosomal anomalies. In conclusion, fetal bowel hyperechogenicity indicates a risk of chromosomal anomalies ten-fold higher than that expected on the basis of maternal age, therefore justifying invasive procedures.

Cystic fibrosis

Although mutation detection rates have not universally reached the 95% detection level recommended by the American Society of Human Genetics and are not likely to exceed 90% for many populations in the foreseeable future, CF carrier screening will probably be offered routinely in the near future. Although CF carrier information will be of benefit to some individuals and couples, the inability of conventional prenatal diagnosis to provide definitive diagnostic outcomes to some couples, specifically those couples in which only one partner has a detectable mutation, will make for considerable anguish and concern for some. Because genetic screening and counseling is meant to provide information and alleviate concerns and fears, the potential for CF screening to result in such a contradictory effect is of a continuing concern to those who provide obstetric and genetic services. In a National Institute of Health-sponsored workshop, Menutti and colleagues recommended that those populations to which carrier screening should be offered might include individuals and couples in high-risk groups (e.g., Ashkenazi Jews, central or northern Europeans, one partner with CF, and individuals with a family history of CF) who seek preconception counseling, infertility care, or prenatal care. The workshop participants concluded, however, that before screening can be offered systematically to these individuals or couples, practice guidelines, educational materials for providers and patients, informed-consent protocols, and laboratory standards for testing must be developed. Further advances in DNA and protein analytic capabilities, such as microchip analytic systems and protein truncation assays, may make CF screening and diagnosis more accurate and less likely to result in equivocal outcomes. In addition, it is hoped that continuing improvements in CF therapies will increase the life expectancy and improve the quality of life for individuals affected with CF. Expanding our current knowledge of genotype-phenotype correlations will not only allow us better to predict clinical outcomes but also may improve our treatments for individuals with CF because more targeted therapies may be developed for CF caused by specific mutations. Nonetheless, educational and counseling issues will, for the foreseeable future, remain of critical importance to ensure appropriate clinical care to low- and high-risk individuals.

Screening practices for mutations in the CFTR gene ABCC7

Cystic fibrosis transmembrane conductance regulator (CFTR) gene studies are now one of the most frequent activities in clinical molecular genetics laboratories. The number of requests is growing, owing to the increasingly wide range of recognized CFTR gene diseases (cystic fibrosis, congenital bilateral absence of the vas deferens, disseminated bronchiectasis, allergic bronchopulmonary aspergillosis and chronic pancreatitis), and the availability of efficient molecular tools for detecting mutations. A growing number of tests capable of simultaneously detecting several frequent CF mutations are being developed, and commercial kits are now available. The most recent kits detect nearly 90% of defective alleles in Caucasians, a rate high enough for carrier screening and for the majority of diagnostic requests. However, because of the wide variety of molecular defects documented in the CFTR gene, only a limited number of laboratories have mastered the entire panoply of necessary techniques, while other laboratories have to refer certain cases to specialized centers with complementary and/or scanning tools at their disposal. A good knowledge of CFTR diseases and their molecular mechanisms, together with expertise in the various techniques, is crucial for interpreting the results. Diagnostic strategies must take into account the indication, the patient's ethnic origin, and the time available in the framework of genetic counseling. This review presents the methods most frequently used for detecting CFTR gene mutations, and discusses the strategies most suited to the different clinical settings.