A novel somatic mutation in GNB2 provides new insights to the pathogenesis of Sturge-Weber syndrome.

Sturge-Weber syndrome (SWS) is a neurocutaneous disorder characterized by vascular malformations affecting skin, eyes and leptomeninges of the brain, which can lead to glaucoma, seizures and intellectual disability. The discovery of a disease-causing somatic missense mutation in the GNAQ gene, encoding an alpha chain of heterotrimeric G-proteins, has initiated efforts to understand how G-proteins contribute to SWS pathogenesis. The mutation is predominantly detected in endothelial cells and is currently believed to affect downstream MAPK signalling. In this study of six Norwegian patients with classical SWS, we aimed to identify somatic mutations through deep sequencing of DNA from skin biopsies. Surprisingly, one patient was negative for the GNAQ mutation, but instead harbored a somatic mutation in GNB2 (NM_005273.3:c.232A>G, p.Lys78Glu), which encodes a beta chain of the same G-protein complex. The positions of the mutant amino acids in the G-protein are essential for complex reassembly. Therefore, failure of reassembly and continuous signalling is a likely consequence of both mutations. Ectopic expression of mutant proteins in endothelial cells revealed that expression of either mutant reduced cellular proliferation, yet regulated MAPK signalling differently, suggesting that dysregulated MAPK signalling cannot fully explain the SWS phenotype. Instead, both mutants reduced synthesis of Yes-associated protein (YAP), a transcriptional co-activator of the Hippo signalling pathway, suggesting a key role for this pathway in the vascular pathogenesis of SWS. The discovery of the GNB2 mutation sheds novel light on the pathogenesis of SWS and suggests that future research on targets of treatment should be directed towards the YAP, rather than the MAPK, signalling pathway.

Biochemical and genetic characterization of an unusual mild PEX3-related Zellweger spectrum disorder.

Patients with PEX3 mutations usually present with a severe form of Zellweger spectrum disorder with death in the first year of life. Whole exome sequencing in adult siblings with intellectual disability revealed a homozygous variant in PEX3 that abolishes the normal splice site. A cryptic acceptor splice site is activated and an in-frame transcript with a deletion is produced. This transcript translates into a protein with residual activity explaining the relatively mild peroxisomal abnormalities and clinical phenotype.

Pathogenic variants in KCTD7 perturb neuronal K+ fluxes and glutamine transport.

Progressive myoclonus epilepsy is a heterogeneous group of disorders characterized by myoclonic and tonic-clonic seizures, ataxia and cognitive decline. We here present two affected brothers. At 9 months of age the elder brother developed ataxia and myoclonic jerks. In his second year he lost the ability to walk and talk, and he developed drug-resistant progressive myoclonus epilepsy. The cerebrospinal fluid level of glutamate was decreased while glutamine was increased. His younger brother manifested similar symptoms from 6 months of age. By exome sequencing of the proband we identified a novel homozygous frameshift variant in the potassium channel tetramerization domain 7 (KCTD7) gene (NM_153033.1:c.696delT: p.F232fs), which results in a truncated protein. The identified F232fs variant is inherited in an autosomal recessive manner, and the healthy consanguineous parents carry the variant in a heterozygous state. Bioinformatic analyses and structure modelling showed that KCTD7 is a highly conserved protein, structurally similar to KCTD5 and several voltage-gated potassium channels, and that it may form homo- or heteromultimers. By heterologous expression in Xenopus laevis oocytes, we demonstrate that wild-type KCTD7 hyperpolarizes cells in a K+ dependent manner and regulates activity of the neuronal glutamine transporter SAT2 (Slc38a2), while the F232fs variant impairs K+ fluxes and obliterates SAT2-dependent glutamine transport. Characterization of four additional disease-causing variants (R94W, R184C, N273I, Y276C) bolster these results and reveal the molecular mechanisms involved in the pathophysiology of KCTD7-related progressive myoclonus epilepsy. Thus, our data demonstrate that KCTD7 has an impact on K+ fluxes, neurotransmitter synthesis and neuronal function, and that malfunction of the encoded protein may lead to progressive myoclonus epilepsy.

Combined inhibition of the cell cycle related proteins Wee1 and Chk1/2 induces synergistic anti-cancer effect in melanoma.

BACKGROUND: Malignant melanoma has an increasing incidence rate and the metastatic disease is notoriously resistant to standard chemotherapy. Loss of cell cycle checkpoints is frequently found in many cancer types and makes the cells reliant on compensatory mechanisms to control progression. This feature may be exploited in therapy, and kinases involved in checkpoint regulation, such as Wee1 and Chk1/2, have thus become attractive therapeutic targets. METHODS: In the present study we combined a Wee1 inhibitor (MK1775) with Chk1/2 inhibitor (AZD7762) in malignant melanoma cell lines grown in vitro (2D and 3D cultures) and in xenografts models. RESULTS: Our in vitro studies showed that combined inhibition of Wee1 and Chk1/2 synergistically decreased viability and increased apoptosis (cleavage of caspase 3 and PARP), which may be explained by accumulation of DNA-damage (increased expression of γ-H2A.X)--and premature mitosis of S-phase cells. Compared to either inhibitor used as single agents, combined treatment reduced spheroid growth and led to greater tumour growth inhibition in melanoma xenografts. CONCLUSIONS: These data provide a rationale for further evaluation of the combination of Wee1 and Chk1/2 inhibitors in malignant melanoma.

STXBP1 encephalopathy: A neurodevelopmental disorder including epilepsy.

OBJECTIVE: To give a comprehensive overview of the phenotypic and genetic spectrum of STXBP1 encephalopathy (STXBP1-E) by systematically reviewing newly diagnosed and previously reported patients. METHODS: We recruited newly diagnosed patients with STXBP1 mutations through an international network of clinicians and geneticists. Furthermore, we performed a systematic literature search to review the phenotypes of all previously reported patients. RESULTS: We describe the phenotypic features of 147 patients with STXBP1-E including 45 previously unreported patients with 33 novel STXBP1 mutations. All patients have intellectual disability (ID), which is mostly severe to profound (88%). Ninety-five percent of patients have epilepsy. While one-third of patients presented with Ohtahara syndrome (21%) or West syndrome (9.5%), the majority has a nonsyndromic early-onset epilepsy and encephalopathy (53%) with epileptic spasms or tonic seizures as main seizure type. We found no correlation between severity of seizures and severity of ID or between mutation type and seizure characteristics or cognitive outcome. Neurologic comorbidities including autistic features and movement disorders are frequent. We also report 2 previously unreported adult patients with prominent extrapyramidal features. CONCLUSION: De novo STXBP1 mutations are among the most frequent causes of epilepsy and encephalopathy. Most patients have severe to profound ID with little correlation among seizure onset, seizure severity, and the degree of ID. Accordingly, we hypothesize that seizure severity and ID present 2 independent dimensions of the STXBP1-E phenotype. STXBP1-E may be conceptualized as a complex neurodevelopmental disorder rather than a primary epileptic encephalopathy.

Generalized epilepsy in a family with basal ganglia calcifications and mutations in SLC20A2 and CHRNB2.

BACKGROUND: The genetic understanding of primary familial brain calcification (PFBC) has increased considerably in recent years due to the finding of causal genes like SLC20A2, PDGFRB and PDGFB. The phenotype of PFBC is complex and has as of yet been poorly delineated. The most common clinical presentations include movement disorders, cognitive symptoms and psychiatric conditions. We report a family including two sisters with brain calcifications due to a variant in SLC20A2 and generalized tonic-clonic seizures as the principal phenotypic trait. METHODS: The affected siblings underwent whole exome sequencing and candidate variants and cosegregation in the family were validated by Sanger sequencing. RESULTS: Both siblings and their asymptomatic father were heterozygous for a variant in SLC20A2. The siblings also had a variant in CHRNB2, a known epilepsy gene associated with autosomal dominant frontal lobe epilepsy, which they had inherited from the mother. CONCLUSIONS: To our knowledge, the reported siblings represent the third and fourth subjects with confirmed SLC20A2 variants exhibiting epilepsy as a phenotypic trait. Our findings support seizures as part of the phenotypic spectrum of SLC20A2-related PFBC. However, the present phenotype may also result from additional genetic influence, such as the identified missense variant in CHRNB2.