BackgroundPontocerebellar hypoplasia (PCH) is a heterogeneous group of diseases characterized by lack of development and/or early neurodegeneration of cerebellum and brainstem. According to clinical features, seven subtypes of PCH have been described, PCH type 2 related to TSEN54 mutations being the most frequent. PCH is most often autosomal recessive though de novo anomalies in the X-linked gene CASK have recently been identified in patients, mostly females, presenting with intellectual disability, microcephaly and PCH (MICPCH).MethodsFourteen patients (12 females and two males; aged 16 months-14 years) presenting with PCH at neuroimaging and with clinical characteristics unsuggestive of PCH1 or PCH2 were included. The CASK gene screening was performed using Array-CGH and sequencing. Clinical and neuroradiological features were collected.ResultsWe observed a high frequency of patients with a CASK mutation (13/14). Ten patients (8 girls and 2 boys) had intragenic mutations and three female patients had a Xp11.4 submicroscopic deletion including the CASK gene. All were de novo mutations. Phenotype was variable in severity but highly similar among the 11 girls and was characterized by psychomotor retardation, severe intellectual disability, progressive microcephaly, dystonia, mild dysmorphism, and scoliosis. Other signs were frequently associated, such as growth retardation, ophthalmologic anomalies (glaucoma, megalocornea and optic atrophy), deafness and epilepsy. As expected in an X-linked disease manifesting mainly in females, the boy hemizygous for a splice mutation had a very severe phenotype with nearly no development and refractory epilepsy. We described a mild phenotype in a boy with a mosaic truncating mutation. We found some degree of correlation between severity of the vermis hypoplasia and clinical phenotype.ConclusionThis study describes a new series of PCH female patients with CASK inactivating mutations and confirms that these patients have a recognizable although variable phenotype consisting of a specific form of pontocerebellar hypoplasia. In addition, we report the second male patient to present with a severe MICPCH phenotype and a de novo CASK mutation and describe for the first time a mildly affected male patient harboring a mosaic mutation. In our reference centre, CASK related PCH is the second most frequent cause of PCH. The identification of a de novo mutation in these patients enables accurate and reassuring genetic counselling.

Aberrant activation or inhibition of potassium (K þ ) 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 þ channel subfamily K member 4 (KCNK4), also known as TRAAK (TWIK-related arachidonic acid-stimulated K þ channel), belongs to the mechano-gated ion channels of the TRAAK/TREK subfamily of two-pore-domain (K2P) K þ 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 þ 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.

Highlights d CD27 dull and CD27 bright MBCs share their VH repertoire but have different functions d CD27 dull MBCs are the long-lived substrate of selected and specific CD27 bright MBCs d The interplay between CD27 dull and CD27 bright MBCs preserves B cell memory d In pregnancy, MBCs decline, but persisting CD27 dull MBCs re-expand after delivery

Ca 2+ in neurons is vital to processes such as neurotransmission, neurotoxicity, synaptic development, and gene expression. Disruption of Ca 2+ homeostasis occurs in brain aging and in neurodegenerative disorders. Membrane transporters, among them the calmodulin (CaM)-activated plasma membrane Ca 2+ ATPases (PMCAs) that extrude Ca 2+ from the cell, play a key role in neuronal Ca 2+ homeostasis. Using X-exome sequencing we have identified a missense mutation (G1107D) in the CaM-binding domain of isoform 3 of the PMCAs in a family with X-linked congenital cerebellar ataxia. PMCA3 is highly expressed in the cerebellum, particularly in the presynaptic terminals of parallel fibers-Purkinje neurons. To study the effects of the mutation on Ca 2+ extrusion by the pump, model cells (HeLa) were cotransfected with expression plasmids encoding its mutant or wild-type (wt) variants and with the Ca 2+ -sensing probe aequorin. The mutation reduced the ability of the PMCA3 pump to control the cellular homeostasis of Ca 2+ . It significantly slowed the return to baseline of the Ca 2+ transient induced by an inositol-trisphosphate (InsP 3 )-linked plasma membrane agonist. It also compromised the ability of the pump to oppose the influx of Ca 2+ through the plasma membrane capacitative channels.calcium dysregulation | plasma membrane calcium pumps | isoforms | X-linked ataxia | cerebellar atrophy T he tight regulation of cell Ca 2+ is crucial for neuronal development, function, and survival. The free Ca 2+ level of neurons at rest is four orders of magnitude lower than in the external medium. Ca 2+ coming from outside or from cellular stores regulates neuronal processes like excitability, neurotransmitter release, synaptic efficacy, and gene expression. The plasma membrane Ca 2+ ATPases (PMCAs) cooperate with the Na + /Ca 2+ exchangers of the plasma membrane (NCX), the endoplasmic reticulum (ER) Ca 2+ -ATPases (SERCA pumps), and the mitochondrial Ca 2+ uptake system in counteracting the transient Ca 2+ increases produced by neuronal stimulation by the influx of Ca 2+ through voltage-and ligand-gated plasma membrane channels, the ER inositol-trisphosphate receptor (InsP 3 R), and the ryanodine receptor (RyR) channels, and through the mitochondrial Ca 2+ release system(s) (1). PMCA isoforms in mammals are the products of 4 separate genes, and the number of variants is increased to over 30 by alternative splicing of mRNAs, which affects the first cytosolic loop of the pump (site A) and its C-terminal tail (site C). The splicing variants are cell-specific and undergo regulation during cell development and differentiation. PMCAs consist of 10 transmembrane domains, 2 large intracellular loops, and N-and C-terminal cytoplasmic tails. The C-terminal tail contains the regulatory calmodulin (CaM)-binding domain, which interacts with two sites in the two cytosolic loops of the pump autoinhibiting the pump at rest: CaM displaces the domain from the two sites restoring full pump activity (2, 3). PMCA1 and PMCA4 are expressed in most tissues, ...