BackgroundFetal akinesia (FA) results in variable clinical presentations and has been associated with more than 166 different disease loci. However, the underlying molecular cause remains unclear in ...many individuals. We aimed to further define the set of genes involved.MethodsWe performed in-depth clinical characterisation and exome sequencing on a cohort of 23 FA index cases sharing arthrogryposis as a common feature.ResultsWe identified likely pathogenic or pathogenic variants in 12 different established disease genes explaining the disease phenotype in 13 index cases and report 12 novel variants. In the unsolved families, a search for recessive-type variants affecting the same gene was performed; and in five affected fetuses of two unrelated families, a homozygous loss-of-function variant in the kinesin family member 21A gene (KIF21A) was found.ConclusionOur study underlines the broad locus heterogeneity of FA with well-established and atypical genotype–phenotype associations. We describe KIF21A as a new factor implicated in the pathogenesis of severe neurogenic FA sequence with arthrogryposis of multiple joints, pulmonary hypoplasia and facial dysmorphisms. This hypothesis is further corroborated by a recent report on overlapping phenotypes observed in Kif21a null piglets.
Neurodevelopmental disorders are major indications for genetic referral and have been linked to more than 1,500 loci including genes encoding transcriptional regulators. The dysfunction of ...transcription factors often results in characteristic syndromic presentations, however, at least half of these patients lack a genetic diagnosis. The implementation of machine learning approaches has the potential to aid in the identification of new disease genes and delineate associated phenotypes. Next generation sequencing was performed in seven affected individuals with neurodevelopmental delay and dysmorphic features. Clinical characterization included reanalysis of available neuroimaging datasets and 2D portrait image analysis with GestaltMatcher. The functional consequences of ZSCAN10 loss were modelled in mouse embryonic stem cells (mESC), including a knock-out and a representative ZSCAN10 protein truncating variant. These models were characterized by gene expression and Western blot analyses, chromatin immunoprecipitation and quantitative PCR (ChIP-qPCR), and immunofluorescence staining. Zscan10 knockout mouse embryos were generated and phenotyped. We prioritized bi-allelic ZSCAN10 loss-of-function variants in seven affected individuals from five unrelated families as the underlying molecular cause. RNA-Seq analyses in Zscan10-/- mESCs indicated dysregulation of genes related to stem cell pluripotency. In addition, we established in mESCs the loss-of-function mechanism for a representative human ZSCAN10 protein truncating variant by showing alteration of its expression levels and subcellular localization, interfering with its binding to DNA enhancer targets. Deep phenotyping revealed global developmental delay, facial asymmetry, and malformations of the outer ear as consistent clinical features. Cerebral MRI showed dysplasia of the semicircular canals as an anatomical correlate of sensorineural hearing loss. Facial asymmetry was confirmed as a clinical feature by GestaltMatcher and was recapitulated in the Zscan10 mouse model along with inner and outer ear malformations. Our findings provide evidence of a novel syndromic neurodevelopmental disorder caused by bi-allelic loss-of-function variants in ZSCAN10.
Objectives
To examine the diagnostic yield of trio exome sequencing in fetuses with multiple structural defects with no pathogenic findings in cytogenetic and microarray analyses.
Methods
We ...recruited 51 fetuses with two or more defects, non‐immune fetal hydrops or fetal akinesia deformation syndrome|or fetal akinesia deformation sequence (FADS). Trio exome sequencing was performed on DNA from chorionic villi samples and parental blood. Detection of genomic variation and prioritization of clinically relevant variants was performed according to in‐house standard operating procedures.
Results
Median maternal and gestational age was 32.0 years and 21.0 weeks, respectively. Forty‐three (84.3%) fetuses had two or more affected organ systems. The remaining fetuses had isolated fetal hydrops or FADS. In total, the exome analysis established the genetic cause for the clinical abnormalities in 22 (43.1%, 95% CI 29.4%–57.8%) pregnancies.
Conclusions
In fetuses with multiple defects, hydrops or FADS and normal standard genetic results, trio exome sequencing has the potential to identify genetic anomalies in more than 40% of cases.
Key points
What's already known about this topic?
Genome‐wide sequencing for unspecific heterogeneous syndromic and non‐syndromic congenital conditions increases the diagnostic yield compared with standard genetic testing in both the pre‐ and postnatal settings. The diagnostic yield prenatally varies depending on selection criteria and number of anomalies present.
What does this study add?
Trio exome sequencing should be considered for fetuses with normal cytogenetic and micro‐array analysis and two or more organ defects, fetal hydrops or fetal akinesia syndromes. Selection of cases for exome sequencing should be based on expert prenatal imaging.
Abstract
Recently, others and we identified de novo FBXO11 (F-Box only protein 11) variants as causative for a variable neurodevelopmental disorder (NDD). We now assembled clinical and mutational ...information on 23 additional individuals. The phenotypic spectrum remains highly variable, with developmental delay and/or intellectual disability as the core feature and behavioral anomalies, hypotonia and various facial dysmorphism as frequent aspects. The mutational spectrum includes intragenic deletions, likely gene disrupting and missense variants distributed across the protein. To further characterize the functional consequences of FBXO11 missense variants, we analyzed their effects on protein expression and localization by overexpression of 17 different mutant constructs in HEK293 and HeLa cells. We found that the majority of missense variants resulted in subcellular mislocalization and/or reduced FBXO11 protein expression levels. For instance, variants located in the nuclear localization signal and the N-terminal F-Box domain lead to altered subcellular localization with exclusion from the nucleus or the formation of cytoplasmic aggregates and to reduced protein levels in western blot. In contrast, variants localized in the C-terminal Zn-finger UBR domain lead to an accumulation in the cytoplasm without alteration of protein levels. Together with the mutational data, our functional results suggest that most missense variants likely lead to a loss of the original FBXO11 function and thereby highlight haploinsufficiency as the most likely disease mechanism for FBXO11-associated NDDs.
PDF
