Project description:Genetic variants in the ABCC9 gene, encoding the SUR2 auxiliary subunit from KATP channels, were previously linked with various inherited diseases. This wide range of congenital disorders includes multisystem and cardiovascular pathologies. The gain-of-function mutations result in Cantu syndrome, acromegaloid facial appearance, hypertrichosis, and acromegaloid facial features. The loss-of-function mutations in the ABCC9 gene were associated with the Brugada syndrome, early repolarization syndrome, and dilated cardiomyopathy. Here, we reported a patient with a loss-of-function variant in the ABCC9 gene, identified by target high-throughput sequencing. The female proband presented with several episodes of ventricular fibrillation and hypokalemia upon emotional stress. This case sheds light on the consequences of KATP channel dysfunction in the cardiovascular system and underlines the complexity of the clinical presentation of ABCC9-related diseases.
Project description:Holoprosencephaly (HPE) is a severe human genetic disease affecting craniofacial development, with an incidence of up to 1/250 human conceptions and 1.3 per 10,000 live births. Mutations in the Sonic Hedgehog (SHH) gene result in HPE in humans and mice, and the Shh pathway is targeted by other mutations that cause HPE. However, at least 12 loci are associated with HPE in humans, suggesting that defects in other pathways contribute to this disease. Although the TGIF1 (TG-interacting factor) gene maps to the HPE4 locus, and heterozygous loss of function TGIF1 mutations are associated with HPE, mouse models have not yet explained how loss of Tgif1 causes HPE. Using a conditional Tgif1 allele, we show that mouse embryos lacking both Tgif1 and the related Tgif2 have HPE-like phenotypes reminiscent of Shh null embryos. Eye and nasal field separation is defective, and forebrain patterning is disrupted in embryos lacking both Tgifs. Early anterior patterning is relatively normal, but expression of Shh is reduced in the forebrain, and Gli3 expression is up-regulated throughout the neural tube. Gli3 acts primarily as an antagonist of Shh function, and the introduction of a heterozygous Gli3 mutation into embryos lacking both Tgif genes partially rescues Shh signaling, nasal field separation, and HPE. Tgif1 and Tgif2 are transcriptional repressors that limit Transforming Growth Factor β/Nodal signaling, and we show that reducing Nodal signaling in embryos lacking both Tgifs reduces the severity of HPE and partially restores the output of Shh signaling. Together, these results support a model in which Tgif function limits Nodal signaling to maintain the appropriate output of the Shh pathway in the forebrain. These data show for the first time that Tgif1 mutation in mouse contributes to HPE pathogenesis and provide evidence that this is due to disruption of the Shh pathway.
Project description:Holoprosencephaly (HPE) is the most common developmental anomaly of the human forebrain; however, the genetics of this heterogeneous and etiologically complex malformation is incompletely understood. Heterozygous mutations in SIX3, a transcription factor gene expressed in the anterior forebrain and eyes during early vertebrate development, have been frequently detected in human HPE cases. However, only a few mutations have been investigated with limited functional studies that would confirm a role in HPE pathogenesis. Here, we report the development of a set of robust and sensitive assays of human SIX3 function in zebrafish and apply these to the analysis of a total of 46 distinct mutations (19 previously published and 27 novel) located throughout the entire SIX3 gene. We can now confirm that 89% of these putative deleterious mutations are significant loss-of-function alleles. Since disease-associated single point mutations in the Groucho-binding eh1-like motif decreases the function in all assays, we can also confirm that this interaction is essential for human SIX3 co-repressor activity; we infer, in turn, that this function is important in HPE causation. We also unexpectedly detected truncated versions with partial function, yet missing a SIX3-encoded homeodomain. Our data indicate that SIX3 is a frequent target in the pathogenesis of HPE and demonstrate how this can inform the genetic counseling of families.
Project description:Diminished Sonic Hedgehog (Shh) signaling is associated with the most common forebrain defect in humans, holoprosencephaly (HPE), which includes cyclopia, a phenotype also seen in mice and other vertebrates with defective Shh signaling. The secreted protein Shh acts as a crucial factor that patterns the ventral forebrain and is required for the division of the primordial eye field and brain into two discrete halves. Gli2 is one of three vertebrate transcription factors implicated as obligatory mediators of Shh signal transduction. Here, we show that loss-of-function mutations in the human GLI2 gene are associated with a distinctive phenotype (within the HPE spectrum) whose primary features include defective anterior pituitary formation and pan-hypopituitarism, with or without overt forebrain cleavage abnormalities, and HPE-like midfacial hypoplasia. We also demonstrate that these mutations lack GLI2 activity. We report on a functional association between GLI2 and human disease and highlight the role of GLI2 in human head development.
Project description:Holoprosencephaly is the incomplete separation of the forebrain during embryogenesis. Both genetic and environmental etiologies have been determined for holoprosencephaly; however, a genetic etiology is not found in most cases. In this report, we present two unrelated individuals with semilobar holoprosencephaly who have the identical de novo missense variant in the gene CCR4-NOT transcription complex, subunit 1 (CNOT1). The variant (c.1603C>T [p.Arg535Cys]) is predicted to be deleterious and is not present in public databases. CNOT1 has not been previously associated with holoprosencephaly or other brain malformations. In situ hybridization analyses of mouse embryos show that Cnot1 is expressed in the prosencephalic neural folds at gestational day 8.25 during the critical period for subsequent forebrain division. Combining human and mouse data, we show that CNOT1 is associated with incomplete forebrain division.
Project description:The utilization of next generation sequencing has been shown to accelerate gene discovery in human disease. However, our confidence in the correct disease-associations of rare variants continues to depend on functional analysis. Here, we employ a sensitive assay of human FGF8 variants in zebrafish to demonstrate that the spectrum of isoforms of FGF8 produced by alternative splicing can provide key insights into the genetic susceptibility to human malformations. In addition, we describe novel mutations in the FGF core structure that have both subtle and profound effects on ligand posttranslational processing and biological activity. Finally, we solve a case of apparent digenic inheritance of novel variants in SHH and FGF8, two genes known to functionally coregulate each other in the developing forebrain, as a simpler case of FGF8 diminished function.
Project description:In this study, a RAD21 variant, R450C, is found associated with a peripheral sclerocornea pedigree. Omics analyses including RNAseq and Hi-C were applied to identify the expression and chromosome conformation of cell adhesion genes were affected by this variant.
Project description:Cornelia de Lange Syndrome (CdLS) is a rare genetic disorder that affects many organs. The diagnosis of this condition is primarily clinical and it can be confirmed by molecular analysis of the genes known to cause this disease, although about 30% of CdLS patients are without a genetic diagnosis. Here we report clinical and genetic findings of a patient with CdLS type 4, a syndrome of which the clinical features of only 30 patients have been previously described in the literature. The index patient presented with clinical characteristics previously associated with CdLS type 4 (short nose, thick eyebrow, global development delay, synophrys, microcephaly, weight < 2DS, small hands, height < 2DS). She also presented cardiac anomalies, cleft palate and laryngomalacia, which was never described before. The index patient was diagnosed with a novel de novo RAD21 variant (c.1722_1723delTG, p.Gly575SerfsTer2): segregation analysis, bioinformatic analysis, population data and in silico structural modelling indicate the pathogenicity of the novel variant. This report summarizes previously reported clinical manifestations of CdLS type 4 but also highlights new clinical symptoms, which will aid correct counselling of future CdLS type 4 cases.