GNB1 Encephalopathy: Clinical Case Report and Literature Review

GNB1 encephalopathy is a rare genetic disease caused by pathogenic variants in the G Protein Subunit Beta 1 (GNB1) gene, with only around 68 cases documented worldwide. Although most cases had been caused by de novo germline mutations, in this case, the pathogenic variant was inherited from patient's mother, indicating an autosomal dominant inheritance pattern. The patient presented at 25 years of age with mild developmental delay and cognitive impairment, prominent generalized dystonia, and horizontal nystagmus which are all characterizing symptoms of GNB1 encephalopathy. Electroencephalography (EEG) showed no epileptiform patterns, and magnetic resonance imaging (MRI) revealed hypointensities in globus pallidus and dentate nucleus areas. The main theory for GNB1 encephalopathy pathogenesis is neuronal hyperexcitability caused by impaired ion channel regulation. Due to low specificity of symptoms, diagnosis relies on genetic testing. As there are no standardized GNB1 encephalopathy treatment guidelines, evaluation of different treatment options is based on anecdotal cases. Reviewing different treatment options, deep brain stimulation and intrathecal baclofen pump, as well as some other medications still in preclinical trials, seem to be the most promising.

GNB1-Related Rod-Cone Dystrophy: A Case Report

Introduction

The GNB1 (guanine nucleotide-binding protein, β1) gene encodes for the ubiquitous β1 subunit of heterotrimeric G proteins, which are associated with G-protein-coupled receptors (GPCRs). GNB1 mutations cause a neurodevelopmental disorder characterized by a broad clinical spectrum. A novel variant has recently been confirmed in a case of rod-cone dystrophy.

Case Presentation

We describe the second confirmed case of a classical rod-cone dystrophy associated with a mutation located in exon 6 of GNB1 [NM_002074.5:c.217G>C, p.(Ala73Pro)] in a 56-year-old patient also presenting mild intellectual disability, attention deficit/hyperactivity disorder, and truncal obesity.

Conclusion

This paper confirms the role of GNB1 in the pathogenesis of a classic rod-cone dystrophy and highlights the importance of including this gene in the genetic analysis panel for inherited retinal diseases.

Case report: Suspecting guanine nucleotide-binding protein beta 1 mutation in dyskinetic cerebral palsy is important

Herein, we describe the case of a 43-month-old girl who presented with clinical manifestations of dyskinetic cerebral palsy (CP), classified as the Gross Motor Function Classification System (GMFCS) V. The patient had no family history of neurological or perinatal disorders. Despite early rehabilitation, serial assessments using the Gross Motor Function Measure (GMFM) showed no significant improvements in gross motor function. Brain magnetic resonance imaging showed nonspecific findings that could not account for developmental delay or dystonia. Whole-genome sequencing identified a heterozygous NM_002074.5(GNB1):c.239T>C (p.Ile80Thr) mutation in guanine nucleotide-binding protein beta 1 (GNB1) gene. Considering this case and previous studies, genetic testing for the etiology of dyskinetic CP is recommended for children without relevant or with nonspecific brain lesions.

Rod-cone dystrophy in an adult with GNB1-related disorder: An expansion of the phenotype and natural history

GNB1-related disorder is characterized by intellectual disability, abnormal tone, and other variable neurologic and systemic features. GNB1 encodes the β1 subunit of the heterotrimeric G-protein, a complex with a key role in signal transduction. Consistent with its particularly high expression in rod photoreceptors, G_β1 forms a subunit of retinal transducin (G_αtβ1γ1 ), which mediates phototransduction. In mice, GNB1 haploinsufficiency has been associated with retinal dystrophy. In humans, however, although vision and eye movement abnormalities are common in individuals with GNB1-related disorder, rod-cone dystrophy is not yet an established feature of this condition. We expand the phenotype of GNB1-related disorder with the first confirmed report of rod-cone dystrophy in an affected individual, and contribute to a further understanding of the natural history of this condition in a mildly affected 45-year-old adult.

Epilepsy in a mouse model of GNB1 encephalopathy arises from altered potassium (GIRK) channel signaling and is alleviated by a GIRK inhibitor

De novo mutations in GNB1, encoding the Gβ1 subunit of G proteins, cause a neurodevelopmental disorder with global developmental delay and epilepsy, GNB1 encephalopathy. Here, we show that mice carrying a pathogenic mutation, K78R, recapitulate aspects of the disorder, including developmental delay and generalized seizures. Cultured mutant cortical neurons also display aberrant bursting activity on multi-electrode arrays. Strikingly, the antiepileptic drug ethosuximide (ETX) restores normal neuronal network behavior in vitro and suppresses spike-and-wave discharges (SWD) in vivo. ETX is a known blocker of T-type voltage-gated Ca2+ channels and G protein-coupled potassium (GIRK) channels. Accordingly, we present evidence that K78R results in a gain-of-function (GoF) effect by increasing the activation of GIRK channels in cultured neurons and a heterologous model (Xenopus oocytes)-an effect we show can be potently inhibited by ETX. This work implicates a GoF mechanism for GIRK channels in epilepsy, identifies a new mechanism of action for ETX in preventing seizures, and establishes this mouse model as a pre-clinical tool for translational research with predicative value for GNB1 encephalopathy.

GNB1 promotes hepatocellular carcinoma progression by targeting BAG2 to activate P38/MAPK signaling

G-proteins are intracellular partners of G-protein-coupled receptors. As a member of the G-protein family, GNB1 has been shown to play a pro-cancer role in lung cancer and breast cancer. However, the biological function and detailed mechanisms of GNB1 in hepatocellular carcinoma progression are unclear. In this study, we investigated the effects of GNB1 and its possible mechanism of action in hepatocellular carcinoma (HCC). The clinical significance of GNB1 was evaluated in a large cohort of HCC patients, showing that GNB1 was overexpressed in HCC compared to adjacent normal liver tissues, and increased GNB1 expression was associated with poor prognosis. We also demonstrated that GNB1 enhances cell proliferation, colony formation, and cell migration and invasion in vitro and promotes the epithelial-to-mesenchymal transition process in HCC cells. Tumor xenograft model assay confirmed the oncogenic role of GNB1 in tumorigenicity in nude mice. Activation of P38 signaling was found in the GNB1 overexpressed HCC cells. Further intervention of P38 confirmed it as an important signaling pathway for the oncogenic role of GNB1 in HCC. Moreover, co-immunoprecipitation followed by liquid chromatograph-mass spectrometry identified that GNB1 exerted oncogenic functions via the interaction of BAG2 and activated P38 signaling pathway. Together, our results reveal that GNB1 plays a pivotal oncogenic role in HCC by promoting the P38 pathway via cooperating with BAG2. GNB1 may serve as a prognostic biomarker for patients with HCC.

Dystonia with myoclonus and vertical supranuclear gaze palsy associated with a rare GNB1 variant

GNB1 encephalopathy (OMIM: 616973), caused by pathogenic variants in the GNB1 gene, is a rare neurodevelopmental syndrome characterized by global developmental delay (GDD) variably co-occurring with movement disorders. For the latter, dystonia, although the most frequent, remains uncommon. Other phenomenologies including myoclonus, tics, chorea, and ataxia, as well as oculomotor abnormalities are rare [1]. Most pathogenic variants in GNBI occur in exons 6 and 7, which are considered to be mutational hotspots [2]. Here, we report a case of GNB1 encephalopathy arising from a de novo mutation in a gene region with few reported pathogenic variants (i.e., exon 11) presenting with a unique phenotype consisting of dystonia with myoclonus and vertical supranuclear gaze palsy.

G Protein Subunit β1 Facilitates Influenza A Virus Replication by Promoting the Nuclear Import of PB2

G protein subunit β1 (GNB1), the beta subunit of the G protein family, plays an important role in regulating transmembrane signal transduction. Although a recent study has demonstrated that GNB1 can bind the matrix protein 1 (M1) to facilitate M1 transport to budding sites and promote the release of progeny influenza A virus (IAV), whether the GNB1 protein has other functions in IAV replication requires further study. Here, we found that GNB1 promoted IAV replication, as virus yield decreased in GNB1 knockdown or knockout cells. GNB1 interacted with polymerase subunits PB2, PB1, and PA. Overexpressed GNB1 facilitated PB2 binding to importin α3, α5, and α7 promoting the nuclear import of PB2, enhancing viral RNA synthesis and polymerase activity. Altogether, our results demonstrated that GNB1 positively regulates virus replication by interacting with polymerase subunits and facilitating the nuclear import of PB2, which provide novel insights into the molecular mechanism of IAV. IMPORTANCE Until now, there has been only one article on the role of GNB1 in IAV budding. No study has investigated the role of GNB1 in IAV replication. In this study, our research demonstrated that GNB1 could increase the interaction between PB2 and the importin α isoform and mediate the nuclear import of PB2. Therefore, GNB1 could promote viral replication and transcription. Our results provide a better understanding of the molecular mechanisms of viral replication and provide potential antiviral drug targets.

BCORL1 S878G, GNB1 G116S, SH2B3 A536T, and KMT2D S3708R tetramutation co-contribute to a pediatric acute myeloid leukemia: Case report and literature review

Acute myeloid leukemia (AML) is a clinically, morphologically, and genetically heterogeneous group of malignancies characterized by a wide range of genomic alterations responsible for defective regulation of the differentiation and self-renewal programs of hematopoietic stem cells. Here, we report a 4-month-old boy who had acute onset with leukocytosis and abdominal mass. The morphological analysis of bone marrow (BM) smear revealed extremely marrow hyperplasia, large quantities of immature cells, and primary and immature monocytic hyperplasia accounting for 57.5% of nucleated cells. The chromosome karyotype of the case was complex, representing 48, XY, +13, +19[12]/48, idem, del (p12)[8]. After RNAs sequencing, a mutation (c.346G > A, p.G116S) of the GNB1 gene was detected and localized to the mutational hotspot in Exon 7. Meanwhile, the other three mutations were identified by next-generation sequencing (NGS) and whole-exome sequencing (WES) of DNA from the BM aspirate and oral swab, including BCORL1 mutation [c.2632A > G, p.S878G, mutation allele frequency (VAF): 99.95%], SH2B3 mutation (c.1606G > A, p.A536T, VAF: 51.17%), and KMT2D mutation (c.11124C > G, p.S3708R, VAF: 48.95%). BCORL1 mutations have been associated with the pathogenesis of AML, whereas other mutations have rarely been previously reported in pediatric AML. The patient did not undergo the combination chemotherapy and eventually died of respiratory failure. In conclusion, the concurrence of BCORL1, GNB1, SH2B3, and KMT2D mutations may be a mutationally detrimental combination and contribute to disease progression.

Case Report: A Novel GNB1 Mutation Causes Global Developmental Delay With Intellectual Disability and Behavioral Disorders

Diseases of neurodevelopment mostly exhibit neurological and psychiatric symptoms that go from very mild to extremely severe. While the etiology of most cases of neurodevelopmental disease is still unknown, the discovery of underlying genetic causes is rapidly increasing, with hundreds of genes being currently implicated as disease-causing. Here, we report a clinical case of a patient with a previously undiagnosed syndrome comprising severe global developmental delay, intellectual disability, and behavioral disorders (such as attention-deficit/hyperactivity disorder, autism spectrum disorder and recurrent bouts of aggressive behavior). After genetic testing, a pathogenic variant was detected in the GNB1 gene, which codes for the G-protein subunit β1. The detected variant (c.217G>A, p.A73T) has not been previously reported in any of the 58 published cases of GNB1 encephalopathy. However, it localizes to the mutational hotspot in exons 6 and 7 in which 88% of all missense mutations occur. An in silico model predicts that this mutation is likely to disrupt the WD40 domain of the GNB1 protein, which is required for its interaction with other G-proteins and, consequently, for downstream signal transduction. In conclusion, we reported an additional GNB1 encephalopathy patient, bearing a novel mutation, taking another step toward a better understanding of its clinical presentation and prospective development of treatments for the disease.

CircRNA circ_POLA2 promotes lung cancer cell stemness via regulating the miR-326/GNB1 axis

Circular RNAs (CircRNAs) are a group of noncoding RNAs that have essential function in the development and progression of various cancers. The expression pattern and function of circRNA in lung cancer is not fully understood. In the present study, we aimed to investigate the expression profiles and underlying mechanism of circRNA circ_POLA2 in lung cancer cell stemness. Circ_POLA2 was highly expressed in lung cancer tissues and predicted a poor prognosis in lung cancer patients. Knockdown of circ_POLA2 inhibited the stemness of lung cancer cells, which is evident by the decreased sphere-formation ability, ALDH1 activity, and stemness marker expression, but had no effects on cell viability. Mechanistically, circ_POLA2 functioned as a ceRNA by sponging miR-326. Furthermore, miR-326 negatively regulated G protein subunit beta 1 (GNB1) expression by targeting its 3'-UTR (untranslated region). Intriguingly, we found that GNB1 was overexpressed and associated with poor prognosis in lung cancer patients. Overexpression of GNB1 could antagonize the inhibitory effect of circ_POLA2 knockdown on lung cancer cell stemness. In conclusion, circ_POLA2 promotes lung cancer cell stemness and progression via regulating the miR-326/GNB1 axis, which might serve as a novel therapeutic target for lung cancer patients.

CircRNA circ_POLA2 Promotes Cervical Squamous Cell Carcinoma Progression via Regulating miR-326/GNB1

Circular RNAs (circRNAs) are a group of non-coding RNAs that have an essential function in the development and progression of various cancers. The expression pattern and function of circRNA in cervical squamous cell carcinoma (CESC) are not fully understood. In the present study, we aimed to investigate the expression profiles and regulation mechanism of circRNA circ_POLA2 in CESC. Circ_POLA2 was highly expressed in CESC tissues and positively correlated with poor prognosis in CESC patients. Knockdown of circ_POLA2 using shRNA inhibited cervical cancer cell proliferation, migration, and invasion both in vitro and in vivo. Mechanistically, circ_POLA2 could sponge endogenous microRNA-326 (miR-326) and inhibit its expression. Furthermore, miR-326 negatively regulated G protein subunit beta 1 (GNB1) by targeting its 3'-UTR. Intriguingly, we found that GNB1 was overexpressed and associated with poor prognosis in CESC patients. Overexpression of GNB1 could antagonize the inhibitory effect of miR-326 on cervical cancer cell proliferation, migration, and invasion. In addition, we demonstrated that circ_POLA2/miR-326/GNB1 axis regulated ERK signaling. In conclusion, circ_POLA2 promotes cervical squamous cell carcinoma development and progression via regulating the miR-326/GNB1 axis, which might serve as a novel therapeutic target for CESC patients.

Recurrent gene mutations detected in canine mast cell tumours by next generation sequencing

Genetic causes of canine mast cell tumours (MCTs), except for mutations in the KIT gene detected in some MCTs, are generally unknown. We used whole exome sequencing to reveal mutation spectra in canine MCTs. We detected somatic mutations in 87 genes including 10 genes recognized as human cancer drivers. Besides KIT, 14 other genes were recurrently mutated. Subsequently, we performed next generation sequencing of a panel of 50 selected genes in additional MCT samples. In this group, the most frequently altered gene was GNB1 showing a recurrent dinucleotide substitution at position of Gly116 in 30% of the MCT samples (n = 6/20) and Ile80 substitution accompanied by a splice region mutation in one case. We extended the study by analysis of the above mentioned GNB1 regions in additional MCT samples by Sanger sequencing, and assessed the overall prevalence of GNB1 mutations to 17.3% (n = 14/81), which is similar to the prevalence of KIT alterations. Our results indicate that GNB1 mutations are probably involved in canine MCT pathogenesis in both cutaneous and subcutaneous MCT cases. As opposed to KIT alterations, the presence of GNB1 mutations did not negatively affect survival times, and our data even showed a trend towards positive prognosis. If our results are confirmed in a larger number of MCTs, an extension of molecular testing of canine MCTs by GNB1 analysis would help to refine the molecular stratification of MCTs, and become useful for targeted treatment strategies.

Phenotype-genotype correlations in patients with GNB1 gene variants, including the first three reported Japanese patients to exhibit spastic diplegia, dyskinetic quadriplegia, and infantile spasms

We report the first three Japanese patients with missense variants in the GNB1 gene. Patients exhibited severe dyskinetic quadriplegia with cortical blindness and epileptic spasms, West syndrome (but with good outcomes), and hypotonic quadriplegia that later developed into spastic diplegia. Whole-exome sequencing revealed two recurrent GNB1 variants (p.Leu95Pro and p.Ile80Thr) and one novel variant (p.Ser74Leu). A recent investigation revealed large numbers of patients with GNB1 variants. Functional studies of such variants and genotype-phenotype correlation are required to enable future precision medicine.

Refining the phenotype associated with GNB1 mutations: Clinical data on 18 newly identified patients and review of the literature

De novo germline mutations in GNB1 have been associated with a neurodevelopmental phenotype. To date, 28 patients with variants classified as pathogenic have been reported. We add 18 patients with de novo mutations to this cohort, including a patient with mosaicism for a GNB1 mutation who presented with a milder phenotype. Consistent with previous reports, developmental delay in these patients was moderate to severe, and more than half of the patients were non-ambulatory and nonverbal. The most observed substitution affects the p.Ile80 residue encoded in exon 6, with 28% of patients carrying a variant at this residue. Dystonia and growth delay were observed more frequently in patients carrying variants in this residue, suggesting a potential genotype-phenotype correlation. In the new cohort of 18 patients, 50% of males had genitourinary anomalies and 61% of patients had gastrointestinal anomalies, suggesting a possible association of these findings with variants in GNB1. In addition, cutaneous mastocytosis, reported once before in a patient with a GNB1 variant, was observed in three additional patients, providing further evidence for an association to GNB1. We will review clinical and molecular data of these new cases and all previously reported cases to further define the phenotype and establish possible genotype-phenotype correlations.