Mutations in KCNK4 that Affect Gating Cause a Recognizable Neurodevelopmental Syndrome

Aberrant activation or inhibition of potassium (K+) currents across the plasma membrane of cells has been causally linked to altered neurotransmission, cardiac arrhythmias, endocrine dysfunction, and (more rarely) perturbed developmental processes. The K+ channel subfamily K member 4 (KCNK4), also known as TRAAK (TWIK-related arachidonic acid-stimulated K+ channel), belongs to the mechano-gated ion channels of the TRAAK/TREK subfamily of two-pore-domain (K2P) K+ channels. While K2P channels are well known to contribute to the resting membrane potential and cellular excitability, their involvement in pathophysiological processes remains largely uncharacterized. We report that de novo missense mutations in KCNK4 cause a recognizable syndrome with a distinctive facial gestalt, for which we propose the acronym FHEIG (facial dysmorphism, hypertrichosis, epilepsy, intellectual disability/developmental delay, and gingival overgrowth). Patch-clamp analyses documented a significant gain of function of the identified KCNK4 channel mutants basally and impaired sensitivity to mechanical stimulation and arachidonic acid. Co-expression experiments indicated a dominant behavior of the disease-causing mutations. Molecular dynamics simulations consistently indicated that mutations favor sealing of the lateral intramembrane fenestration that has been proposed to negatively control K+ flow by allowing lipid access to the central cavity of the channel. Overall, our findings illustrate the pleiotropic effect of dysregulated KCNK4 function and provide support to the hypothesis of a gating mechanism based on the lateral fenestrations of K2P channels

Paediatric-type diffuse high-grade gliomas in the 5th CNS WHO Classification

As a relevant element of novelty, the fifth CNS WHO Classification highlights the distinctive pathobiology underlying gliomas arising primarily in children by recognizing for the first time the families of paediatric-type diffuse gliomas, both high-grade and low-grade. This review will focus on the family of paediatric-type diffuse high-grade gliomas, which includes four tumour types: 1) Diffuse midline glioma H3 K27-altered; 2) Diffuse hemispheric glioma H3 G34-mutant; 3) Diffuse paediatric-type high-grade glioma H3-wildtype and IDH-wildtype; and 4) Infant-type hemispheric glioma. The essential and desirable diagnostic criteria as well as the entities entering in the differential will be discussed for each tumour type. A special focus will be given on the issues encountered in the daily practice, especially regarding the diagnosis of the diffuse paediatric-type high-grade glioma H3-wildtype and IDH-wildtype. The advantages and the limits of the multiple molecular tests which may be utilised to define the entities of this tumour family will be evaluated in each diagnostic context

TBCE Mutations Cause Early-Onset Progressive Encephalopathy with Distal Spinal Muscular Atrophy

Tubulinopathies constitute a family of neurodevelopmental/neurodegenerative disorders caused by mutations in several genes encoding tubulin isoforms. Loss-of-function mutations in TBCE, encoding one of the five tubulin-specific chaperones involved in tubulin folding and polymerization, cause two rare neurodevelopmental syndromes, hypoparathyroidism-retardation-dysmorphism and Kenny-Caffey syndrome. Although a missense mutation in Tbce has been associated with progressive distal motor neuronopathy in the pmn/pmn mice, no similar degenerative phenotype has been recognized in humans. We report on the identification of an early-onset and progressive neurodegenerative encephalopathy with distal spinal muscular atrophy resembling the phenotype of pmn/pmn mice and caused by biallelic TBCE mutations, with the c.464T>A (p.Ile155Asn) change occurring at the heterozygous/homozygous state in six affected subjects from four unrelated families originated from the same geographical area in Southern Italy. Western blot analysis of patient fibroblasts documented a reduced amount of TBCE, suggestive of rapid degradation of the mutant protein, similarly to what was observed in pmn/pmn fibroblasts. The impact of TBCE mutations on microtubule polymerization was determined using biochemical fractionation and analyzing the nucleation and growth of microtubules at the centrosome and extracentrosomal sites after treatment with nocodazole. Primary fibroblasts obtained from affected subjects displayed a reduced level of polymerized α-tubulin, similarly to tail fibroblasts of pmn/pmn mice. Moreover, markedly delayed microtubule re-polymerization and abnormal mitotic spindles with disorganized microtubule arrangement were also documented. Although loss of function of TBCE has been documented to impact multiple developmental processes, the present findings provide evidence that hypomorphic TBCE mutations primarily drive neurodegeneration

The Interplay between CD27dull and CD27bright B Cells Ensures the Flexibility, Stability, and Resilience of Human B Cell Memory

Summary: Memory B cells (MBCs) epitomize the adaptation of the immune system to the environment. We identify two MBC subsets in peripheral blood, CD27dull and CD27bright MBCs, whose frequency changes with age. Heavy chain variable region (VH) usage, somatic mutation frequency replacement-to-silent ratio, and CDR3 property changes, reflecting consecutive selection of highly antigen-specific, low cross-reactive antibody variants, all demonstrate that CD27dull and CD27bright MBCs represent sequential MBC developmental stages, and stringent antigen-driven pressure selects CD27dull into the CD27bright MBC pool. Dynamics of human MBCs are exploited in pregnancy, when 50% of maternal MBCs are lost and CD27dull MBCs transit to the more differentiated CD27bright stage. In the postpartum period, the maternal MBC pool is replenished by the expansion of persistent CD27dull clones. Thus, the stability and flexibility of human B cell memory is ensured by CD27dull MBCs that expand and differentiate in response to change. : Grimsholm et al. show that CD27dull and CD27bright represent sequential MBC developmental stages. T cell- and germinal center (GC)-independent CD27dull MBCs are the plastic source of strongly selected and GC-dependent CD27bright MBCs. CD27dull MBCs, able to expand and differentiate in response to change, ensure stability and flexibility of human B cell memory. Keywords: memory B cells, pregnancy, immunological memory, CD27, VH repertoire, immunodeficiency, aging, spleen, vaccine, germinal cente

Loss-of-function mutations in UDP-Glucose 6-Dehydrogenase cause recessive developmental epileptic encephalopathy

AbstractDevelopmental epileptic encephalopathies are devastating disorders characterized by intractable epileptic seizures and developmental delay. Here, we report an allelic series of germline recessive mutations in UGDH in 36 cases from 25 families presenting with epileptic encephalopathy with developmental delay and hypotonia. UGDH encodes an oxidoreductase that converts UDP-glucose to UDP-glucuronic acid, a key component of specific proteoglycans and glycolipids. Consistent with being loss-of-function alleles, we show using patients’ primary fibroblasts and biochemical assays, that these mutations either impair UGDH stability, oligomerization, or enzymatic activity. In vitro, patient-derived cerebral organoids are smaller with a reduced number of proliferating neuronal progenitors while mutant ugdh zebrafish do not phenocopy the human disease. Our study defines UGDH as a key player for the production of extracellular matrix components that are essential for human brain development. Based on the incidence of variants observed, UGDH mutations are likely to be a frequent cause of recessive epileptic encephalopathy.</jats:p

Loss-of-function mutations in UDP-Glucose 6-Dehydrogenase cause recessive developmental epileptic encephalopathy

Developmental epileptic encephalopathies are devastating disorders characterized by intractable epileptic seizures and developmental delay. Here, we report an allelic series of germline recessive mutations in UGDH in 36 cases from 25 families presenting with epileptic encephalopathy with developmental delay and hypotonia. UGDH encodes an oxidoreductase that converts UDP-glucose to UDP-glucuronic acid, a key component of specific proteoglycans and glycolipids. Consistent with being loss-of-function alleles, we show using patients’ primary fibroblasts and biochemical assays, that these mutations either impair UGDH stability, oligomerization, or enzymatic activity. In vitro, patient-derived cerebral organoids are smaller with a reduced number of proliferating neuronal progenitors while mutant ugdh zebrafish do not phenocopy the human disease. Our study defines UGDH as a key player for the production of extracellular matrix components that are essential for human brain development. Based on the incidence of variants observed, UGDH mutations are likely to be a frequent cause of recessive epileptic encephalopathy

Histone H3.3 beyond cancer: Germline mutations in Histone 3 Family 3A and 3B cause a previously unidentified neurodegenerative disorder in 46 patients

Although somatic mutations in Histone 3.3 (H3.3) are well-studied drivers of oncogenesis, the role of germline mutations remains unreported. We analyze 46 patients bearing de novo germline mutations in histone 3 family 3A (H3F3A) or H3F3B with progressive neurologic dysfunction and congenital anomalies without malignancies. Molecular modeling of all 37 variants demonstrated clear disruptions in interactions with DNA, other histones, and histone chaperone proteins. Patient histone posttranslational modifications (PTMs) analysis revealed notably aberrant local PTM patterns distinct from the somatic lysine mutations that cause global PTM dysregulation. RNA sequencing on patient cells demonstrated up-regulated gene expression related to mitosis and cell division, and cellular assays confirmed an increased proliferative capacity. A zebrafish model showed craniofacial anomalies and a defect in Foxd3-derived glia. These data suggest that the mechanism of germline mutations are distinct from cancer-associated somatic histone mutations but may converge on control of cell proliferation

CNS tumor with CREBBP::BCORL1 Fusion and pathogenic mutations in BCOR and CREBBP: expanding the spectrum of BCOR-altered tumors

: The fifth edition of the World Health Organization (WHO) classification of central nervous system (CNS) tumors introduced the new tumor type CNS tumor with BCOR internal tandem duplication (ITD), characterized by a distinct DNA methylation profile and peculiar histopathological features, including a circumscribed growth pattern, ependymoma-like perivascular pseudorosettes, microcystic pattern, absent or focal GFAP immunostaining, OLIG2 positivity, and BCOR immunoreactivity. We describe a rare case of a CNS tumor in a 45-year-old man with histopathological and immunohistochemical features overlapping the CNS tumor with BCOR internal tandem duplication (ITD) but lacking BCOR immunostaining and BCOR ITD. Instead, the tumor showed CREBBP::BCORL1 fusion and pathogenic mutations in BCOR and CREBBP, along with a DNA methylation profile matching the "CNS tumor with EP300:BCOR(L1) fusion" methylation class. Two CNS tumors with fusions between CREBBP, or its paralog EP300, and BCORL1, and approximately twenty CNS tumors with CREBBP/EP300::BCOR fusions have been reported to date. They exhibited similar ependymoma-like features or a microcystic pattern, along with focal or absent GFAP immunostaining, and shared the same DNA methylation profile. Given their morphological and epigenetic similarities, circumscribed CNS tumors with EP300/CREBBP::BCOR(L1) fusions and CNS tumors with BCOR ITD may represent variants of the same tumor type. The ependymoma-like aspect coupled with the lack of diffuse GFAP immunostaining and the presence of OLIG2 positivity are useful clues for recognizing these tumors in histopathological practice. The diagnosis should be confirmed after testing for BCOR(L1) gene fusions and BCOR ITD

Angioimmunoblastic T-Cell Lymphoma with Exuberant CD30-Positive Follicular Dendritic Cell Proliferation in a SARS-CoV-2 Patient: The Role of Mutational Analysis to Exclude an Associated Follicular Dendritic Cell Sarcoma

Follicular dendritic cell (FDC) proliferation in angioimmunoblastic T-cell lymphoma (AITL) is still not well defined, challenging the accurate differential diagnosis between the AITL with expanded follicular dendritic cell meshwork and the combined AITL and follicular dendritic cell sarcoma (FDCS). Herein, we reported the case of a 58-year-old male with coexisting SARS-CoV-2 infection and AITL with an exuberant CD30-positive FDC proliferation, in which genetic analysis identified mutations of genes commonly involved in AITL but not in FDC sarcoma (i.e., RHOA, TET2, DNMT3A, and IDH2), thus supporting the reactive nature of the CD30-positive FDC expansion

Oligophrenin-1 (OPHN1), a gene involved in X-linked intellectual disability, undergoes RNA editing and alternative splicing during human brain development.

Oligophrenin-1 (OPHN1) encodes for a Rho-GTPase-activating protein, important for dendritic morphogenesis and synaptic function. Mutations in this gene have been identified in patients with X-linked intellectual disability associated with cerebellar hypoplasia. ADAR enzymes are responsible for A-to-I RNA editing, an essential post-transcriptional RNA modification contributing to transcriptome and proteome diversification. Specifically, ADAR2 activity is essential for brain development and function. Herein, we show that the OPHN1 transcript undergoes post-transcriptional modifications such as A-to-I RNA editing and alternative splicing in human brain and other tissues. We found that OPHN1 editing is detectable already at the 18th week of gestation in human brain with a boost of editing at weeks 20 to 33, concomitantly with OPHN1 expression increase and the appearance of a novel OPHN1 splicing isoform. Our results demonstrate that multiple post-transcriptional events occur on OPHN1, a gene playing an important role in brain function and development