Prenatal Diagnosis of Walker-Warburg Syndrome due to Compound Mutations in the B3GALNT2 Gene

Compound heterozygous B3GALNT2 mutations in a fetus with encephalocele: A case report

An encephalocele is a congenital malformation characterized by protrusion of the intracranial contents through a cranial defect. We report that a fetus of a pregnant mother who had two consecutive pregnancies with ultrasound-detected encephalocele carried compound heterozygous variants in B3GALNT2 NM_152490.5:c.[1423C > T (p.Gln475Ter)]; [261-2A > G] of maternal and paternal origins, respectively, as confirmed by exome sequencing followed by Sanger sequencing validation. The present case implies that mutations in B3GALNT2, a well-known dystroglycanopathy causative gene, may result in a phenotype of neural tube defect, providing new insights into the clinical spectrum of B3GALNT2-related disorders. Our study may contribute to prenatal screening/diagnosis and genetic counseling of congenital brain malformations.

Diagnostic yield with exome sequencing in prenatal severe bilateral ventriculomegaly: a systematic review and meta-analysis

OBJECTIVE

This study aimed to determine the incremental diagnostic yield of prenatal exome sequencing after negative chromosomal microarray analysis results in prenatally diagnosed bilateral severe ventriculomegaly or hydrocephalus; another objective was to categorize the associated genes and variants.

DATA SOURCES

A systematic search was performed to identify relevant studies published until June 2022 using 4 databases (Cochrane Library, Web of Science, Scopus, and MEDLINE).

STUDY ELIGIBILITY CRITERIA

Studies in English reporting on the diagnostic yield of exome sequencing following negative chromosomal microarray analysis results in cases of prenatally diagnosed bilateral severe ventriculomegaly were included.

METHODS

Authors of cohort studies were contacted for individual participant data, and 2 studies provided their extended cohort data. The incremental diagnostic yield of exome sequencing was assessed for pathogenic/likely pathogenic findings in cases of: (1) all severe ventriculomegaly; (2) isolated severe ventriculomegaly (as the only cranial anomaly); (3) severe ventriculomegaly with other cranial anomalies; and (4) nonisolated severe ventriculomegaly (with extracranial anomalies). To be able to identify all reported genetic associations, the systematic review portion was not limited to any minimal severe ventriculomegaly case numbers; however, for the synthetic meta-analysis, we included studies with ≥3 severe ventriculomegaly cases. Meta-analysis of proportions was done using a random-effects model. Quality assessment of the included studies was performed using the modified STARD (Standards for Reporting of Diagnostic Accuracy Studies) criteria.

RESULTS

A total of 28 studies had 1988 prenatal exome sequencing analyses performed following negative chromosomal microarray analysis results for various prenatal phenotypes; this included 138 cases with prenatal bilateral severe ventriculomegaly. We categorized 59 genetic variants in 47 genes associated with prenatal severe ventriculomegaly along with their full phenotypic description. There were 13 studies reporting on ≥3 severe ventriculomegaly cases, encompassing 117 severe ventriculomegaly cases that were included in the synthetic analysis. Of all the included cases, 45% (95% confidence interval, 30-60) had positive pathogenic/likely pathogenic exome sequencing results. The highest yield was for nonisolated cases (presence of extracranial anomalies; 54%; 95% confidence interval, 38-69), followed by severe ventriculomegaly with other cranial anomalies (38%; 95% confidence interval, 22-57) and isolated severe ventriculomegaly (35%; 95% confidence interval, 18-58).

CONCLUSION

There is an apparent incremental diagnostic yield of prenatal exome sequencing following negative chromosomal microarray analysis results in bilateral severe ventriculomegaly. Although the greatest yield was found in cases of nonisolated severe ventriculomegaly, consideration should also be given to performing exome sequencing in cases of isolated severe ventriculomegaly as the only brain anomaly identified on prenatal imaging.