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.

The effect of associated structural malformations in the prediction of chromosomal abnormality risk of fetuses with echogenic bowel.

OBJECTIVE: Our aim is to determine the frequency of chromosomal abnormalities and also to identify the role of structural malformations on the chromosomal abnormality risk among fetuses with echogenic bowel. METHODS: Over a 6-year period fetuses with echogenic bowel (FEB) were retrospectively evaluated. The pregnancies with intra-amniotic bleeding history, congenital infection, cystic fibrosis and intrauterine growth retardation were excluded from the study. Types and frequency of sonographically detected fetal malformations were identified. Chromosomal abnormality incidences according to association with soft markers and major fetal abnormalities were compared. RESULTS: Of the 281 fetuses with echogenic bowel, 105 (37.37%) were isolated, 78 (27.76%) were associated with soft markers and 98 (34.87%) were associated with major abnormalities. There were 30 (10.7%) fetuses with abnormal karyotypes. The chromosomal abnormality rate of the groups of isolated FEB, FEB + soft markers and FEB + major abnormalities were 6.7%, 7.7% and 17.4%, respectively. CONCLUSIONS: Chromosomal abnormality risk in fetuses with echogenic bowel should be evaluated according to additional sonographic findings. Association of structural malformations increases the chromosomal abnormality risk, although this risk is not significant with the presence of soft markers alone.

Mid-trimester hyperechogenic bowel in a fetus of Turkish origin carrying a rarely seen mutation of cystic fibrosis.

Cystic fibrosis (CF) is one of the most common severe autosomal recessive genetic disorders, characterized primarily by chronic obstructive lung disease and maldigestion disorder. The disease is caused by mutations in the CF transmembrane conductance regulator (CFTR) gene. Here we present a case of a fetus with hyperechogenic bowel, in which compound heterozygosity was established for the mutations p.IIe1000fsX1001 and p.Asp110His subsequent to amniocentesis. The mutations were most likely disease-causing, and pregnancy was terminated.

Nonvisualization of fetal gallbladder increases the risk of cystic fibrosis.

OBJECTIVE: The aim of our study is to evaluate the prevalence of cystic fibrosis (CF) in fetuses referred for genetic testing because of ultrasonographic sign (nonvisualized fetal gallbladder--NVFGB). METHOD: We reviewed the results of CFTR gene analysis over the period 2002 to 2009 in all consecutive cases referred because of NVFGB in Western France. We correlated these data with the presence of a more classical ultrasonographic finding (fetal echogenic bowel - FEB). RESULTS: Cystic fibrosis was diagnosed in 5 of the 37 fetuses with NVFGB (13.5%, 95% confidence interval (CI): [2.5%; 24.5%]) and in only 9 of the 229 other cases referred because of FEB (3.9%, 95% CI: [3.2%; 14.7%]). In our series, all CF-affected fetuses with NVFGB also had FEB. The risk of CF was 11.6-fold higher in fetuses with both indications (NVFGB + FEB) than in fetuses with isolated FEB (45.5% vs 3.9%, RR = 11.6, 95% CI: [4.7%; 28.8%], p = 0.0001). We also estimated that the residual risk of CF was less than 1 in 68 (1.5%) when a single mutation was identified in the fetus by our molecular protocol. CONCLUSION: Ultrasonographic evidence of NVFGB is an additional risk factor for CF in cases with FEB.

Comprehensive description of CFTR genotypes and ultrasound patterns in 694 cases of fetal bowel anomalies: a revised strategy.

Fetal bowel anomalies may reveal cystic fibrosis (CF) and the search for CF transmembrane conductance regulator (CFTR) gene mutations is part of the diagnostic investigations in such pregnancies, according to European recommendations. We report on our 18-year experience to document comprehensive CFTR genotypes and correlations with ultrasound patterns in a series of 694 cases of fetal bowel anomalies. CFTR gene analysis was performed in a multistep process, including search for frequent mutations in the parents and subsequent in-depth search for rare mutations, depending on the context. Ultrasound patterns were correlated with the genotypes. Cases were distinguished according to whether they had been referred directly to our laboratory or after an initial testing in another laboratory. A total of 30 CF fetuses and 8 cases compatible with CFTR-related disorders were identified. CFTR rearrangements were found in 5/30 CF fetuses. 21.2% of fetuses carrying a frequent mutation had a second rare mutation, indicative of CF. The frequency of CF among fetuses with no frequent mutation was 0.43%. Correlation with ultrasound patterns revealed a significant frequency of multiple bowel anomalies in CF fetuses. The results emphasize the need to search for rearrangements in the diagnosis strategy of fetal bowel anomalies. The diagnostic value of ultrasound patterns combining hyperechogenic bowel, loop dilatation and/or non-visualized gallbladder reveals a need to revise current strategies and to offer extensive CFTR gene testing when the triad is diagnosed, even when no frequent mutation is found in the first-step analysis.

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.

Outcomes for fetal echogenic bowel during the second trimester ultrasound.

OBJECTIVE: To investigate the association between fetal echogenic bowel (FEB) during the second trimester and perinatal outcome. METHODS: A retrospective chart review of FEB during the second trimester over 3 years. RESULTS: A total of 56 women were identified of 9067 screened (0.6%) women. Forty-seven agreed to genetic counseling (84%). Of those, 22 (39%) agreed to an amniocentesis. There were three cases of trisomy 21, one case of trisomy 18 and one case of fetal CMV infection. Twelve fetuses had an adverse outcome (21%), with only three of them having an echogenic bowel as the only finding. CONCLUSIONS: In our study, almost 80% of the fetuses had an uncomplicated perinatal outcome. FEB was present as the only finding in only 5% of the fetuses with an adverse outcome. A potential association with placental abnormalities and a low prevalence of viral infections was observed. These findings may be of use in counseling parents.