Strengths and limitations
Twenty-three percent of the patients who were sequenced had an increased fetal nuchal translucency or cystic hygroma, and another 17% had a single fetal effusion. This inclusivity makes this study more applicable to broader fetal anomaly populations. However, it is worth noting that only 61% of patients had NIHF by the definition of 2 or more fluid collections or skin thickening.
The authors assumed 100% sensitivity and specificity for the panel tests relative to diagnostic ES results, but this may not reflect real-life analysis. There is inherent subjectivity and subsequent differences in variant calling (deciding which genetic changes are pathogenic) between institutions and companies despite efforts to standardize this process. Due to the simulated nature of this study, these differences are not captured. Additionally, although the authors note that the research ES had at least 30 times the coverage (an adequate number of sequence reads for accurate testing) than did the commercial lab panels, some gene panels have additional sequencing of intronic regions, copy number analysis, and up to 10 times more coverage than ES, which could lead to more diagnoses.
This study illustrates that there is nuance involved in selecting which type of gene sequencing and which clinical laboratory to use for prenatal diagnosis. Labs with more updated literature searches and more inclusive gene panels may be excellent options for patients in whom ES is not covered by insurance or with phenotypes with a narrow range of suspected causative genes. However, there is a lag time in updating the genes offered on each panel, and new genedisease associations will not be captured by existing panels.
From a cost, speed-of-analysis, and depth-of-sequencing perspective, panel sequencing can have advantages that should be considered in some patients, particularly if the panels are large and regularly updated. However, the authors summarize our sentiments and their findings with the following:
“For disorders, such as NIHF with marked genetic heterogeneity and less clear in utero phenotypes of underlying genetic diseases, the broader coverage of exome sequencing makes it a superior option to targeted panel testing.”
We look forward to the publication of further anomaly-specific cohorts and secondary analyses of the utility of current panels and ES that may follow.
Frequency of Beckwith-Widemann syndrome in prenatally diagnosed omphaloceles
Abbasi N, Moore A, Chiu P, et al. Prenatally diagnosed omphaloceles: report of 92 cases and association with Beckwith-Wiedemann syndrome. Prenat Diagn. 2021;41:798-816. doi:10.1002/pd.5930.
An omphalocele is diagnosed prenatally on ultrasound when an anterior midline mass, often containing abdominal contents, is seen herniating into the base of the umbilical cord. Omphaloceles are often associated with additional structural abnormalities and underlying genetic syndromes, thus a thorough fetal assessment is required for accurate prenatal counseling and neonatal care.
Identification of Beckwith-Widemann syndrome (BWS) in the setting of a prenatally diagnosed omphalocele is difficult because of its wide range of clinical features and its unique genetic basis. Unlike many genetic disorders that are caused by specific genetic variants, or spelling changes in the genes, BWS results from a change in the expression of one or more of the genes in a specific region of chromosome 11. A high index of clinical suspicion as well as an understanding of the various genetic and epigenetics alterations that cause BWS is required for prenatal diagnosis.
Retrospective cohort at a single center
The authors in this study reviewed all pregnancies in which an omphalocele was diagnosed prenatally at a single center between 2010 and 2015. They describe a standard prenatal evaluation following identification of an omphalocele including echocardiogram, detailed anatomic survey, and availability of an amniocentesis to facilitate aneuploidy screening and testing for BWS. This review also includes an overview of perinatal and long-term outcomes for cases of BWS diagnosed at their center between 2000 and 2015.
Study outcomes
Results of prenatal genetic testing in this cohort were divided between cases of an isolated omphalocele (without other structural changes) and cases of nonisolated omphaloceles. In the group of pregnancies with an isolated omphalocele, 2 of 27 pregnancies (7.4%) were found to have an abnormal karyotype, and 6 of 16 of the remaining pregnancies (37.5%) were diagnosed with BWS. Among the group of pregnancies with a nonisolated omphalocele, 23 of 59 pregnancies (39%) were found to have an abnormal karyotype, and 1 of 20 pregnancies (5%) were diagnosed with BWS.
Prenatal sonographic features associated with cases of BWS included polyhydramnios in 12 of 19 cases (63%) and macrosomia in 8 of 19 cases (42%). Macroglossia is another characteristic feature of the disorder, which was identified in 4 of 19 cases (21%) prenatally and in an additional 10 of 19 cases (52.6%) postnatally. Interestingly, only 1 of the cases of BWS was caused by a microdeletion at 11p15.4—a change that was identified on microarray. The additional 6 cases of BWS were caused by imprinting changes in the region, which are only detectable with a specific methylation-analysis technique.
Among the 19 cases of BWS identified over a 15-year period, there was 1 intrauterine demise. Preterm birth occurred in 10 of 19 cases (52.6%), including 8 of 19 cases (42.1%) of spontaneous preterm labor. Respiratory distress (27.8%), hypoglycemia (61%), and gastrointestinal reflux (59%) were common neonatal complications. Embryonal tumors were diagnosed in 2 of 16 patients (12.5%). Although neurodevelopmental outcomes were incomplete, their data suggested normal development in 75% of children. There were 2 neonatal deaths in this cohort and 1 childhood death at age 2 years.
Study strengths and limitations
As with many studies investigating a rare disorder, this study is limited by its retrospective nature and small sample size. Nevertheless, it adds an important cohort of patients with a prenatally diagnosed omphalocele to the literature and illuminates the utility of a standardized approach to testing for BWS in this population.
In this cohort with prenatally diagnosed omphaloceles with standardized testing for BWS, the prevalence of the disorder was approximately 8% and more common in cases of an isolated omphalocele. The most common supporting sonographic features of BWS may not be detected until later in gestation, including polyhydramnios and macrosomia. This demonstrates the importance of both sonographic follow-up as well as universal testing for BWS in euploid cases of a prenatally diagnosed omphalocele. Almost all cases of BWS in this cohort required specialized molecular techniques for diagnosis, and the diagnosis would have been missed on karyotype, microarray, and ES.
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