P/Q-type channels are the principal presynaptic calcium channels in brain functioning in neurotransmitter release. They are composed of the pore-forming Ca_V2.1 α₁ subunit and the auxiliary α2δ-2 and β₄ subunits. β₄ is encoded by CACNB4, and its multiple splice variants serve isoform-specific functions as channel subunits and transcriptional regulators in the nucleus. In two siblings with intellectual disability, psychomotor retardation, blindness, epilepsy, movement disorder and cerebellar atrophy we identified rare homozygous variants in the genes LTBP1, EMILIN1, CACNB4, MINAR1, DHX38 and MYO15 by whole-exome sequencing. In silico tools, animal model, clinical, and genetic data suggest the p.(Leu126Pro) CACNB4 variant to be likely pathogenic. To investigate the functional consequences of the CACNB4 variant, we introduced the corresponding mutation L125P into rat β_4b cDNA. Heterologously expressed wild-type β_4b associated with GFP-Ca_V1.2 and accumulated in presynaptic boutons of cultured hippocampal neurons. In contrast, the β_4b-L125P mutant failed to incorporate into calcium channel complexes and to cluster presynaptically. When co-expressed with Ca_V2.1 in tsA201 cells, β_4b and β_4b-L125P augmented the calcium current amplitudes, however, β_4b-L125P failed to stably complex with α₁ subunits. These results indicate that p.Leu125Pro disrupts the stable association of β_4b with native calcium channel complexes, whereas membrane incorporation, modulation of current density and activation properties of heterologously expressed channels remained intact. Wildtype β_4b was specifically targeted to the nuclei of quiescent excitatory cells. Importantly, the p.Leu125Pro mutation abolished nuclear targeting of β_4b in cultured myotubes and hippocampal neurons. While binding of β_4b to the known interaction partner PPP2R5D (B56δ) was not affected, complex formation between β_4b-L125P and the neuronal TRAF2 and NCK interacting kinase (TNIK) seemed to be disturbed. In summary, our data suggest that the homozygous CACNB4 p.(Leu126Pro) variant underlies the severe neurological phenotype in the two siblings, most likely by impairing both channel and non-channel functions of β_4b. Neurodevelopmental disorders encompass a broad spectrum of neurological and psychiatric conditions and are caused by mutations in many different genes. For example, mutations in genes encoding voltage-gated calcium channels have been linked to various diseases of the nervous system in humans and mice. Voltage-gated calcium channels are critical regulators of the synaptic communication between neurons, of processes involved in learning and memory, and of activity-dependent gene expression. Here we report a disease-associated mutation on both copies of the CACNB4 gene encoding an auxiliary β₄ subunit of the chief presynaptic calcium channel in the brain. Two siblings with a severe neurodevelopmental disorder carry the homozygous CACNB4 mutation causing an amino acid substitution known to disrupt the folding of the calcium channel β₄ subunit. We demonstrate that this amino acid change abolished the incorporation of the β₄ subunit into channel complexes in the synapse, as well as β₄’s ability to translocate into the cell nucleus, and to complex with α₁ channel subunits and a neuronal scaffolding protein. The combined evidence from our genetic and functional analysis suggests that dysfunction of both β₄ subunit channel and non-channel functions underlies the severe neurological phenotype in the two siblings. We therefore identified CACNB4 as a neurodevelopmental disease gene.

To assess uni- and multisensory development in humans, uni- and crossmodal event-related potential (ERP) refractory period effects were investigated. Forty-one children from 4 to 12 years of age and 15 young adults performed a bimodal oddball task with frequent and rare visual and auditory stimuli presented with two different interstimulus intervals (ISI). Amplitudes of the visual and auditory ERPs were modulated as a function of the age of the participants, the modality of the preceding stimulus (same vs. different) and the preceding interstimulus interval (1000 or 2000 ms). While unimodal refractory period effects were observed in all age groups, crossmodal refractory period effects differed among age groups. Early crossmodal interactions (150 ms) emerged with a parietal topography in older children and adults. Our results are compatible with the intersensory differentiation and the multisensory perceptual narrowing approach of multisensory development. Moreover, our data suggest that uni- and multisensory development run in parallel with unimodal development leading.

Background: Life extension by medical interventions and health-related quality of life (HRQOL) are sometimes conflicting aspects of medical care. Long-term ventilation in children with neuromuscular disease is a well-established life-extending procedure and often at the center of this conflict. HRQOL and the mental health of affected children and their families become even more important in respect to emerging therapies in neuromuscular diseases with longer life-expectancy of treated patients and considerable costs of medical treatment. Methods: We performed a questionnaire survey in a total of forty-three families of children with neuromuscular disease treated in the University Medical Center Hamburg-Eppendorf and the Children’s Hospital Altona. We evaluated self- and proxy-reported HRQOL and mental health outcomes of affected children and their parents using validated and age-appropriate instruments. Results: Compared to normative data, children with neuromuscular diseases and their families experienced a lower HRQOL and mental health. However, there was no additional negative influence on the overall HRQOL by ventilator use. Conclusions: As ventilator use was not responsible for the reduction of HRQOL and mental health our data contributes an important aspect to the discussion about life-prolonging procedures, in particular mechanical ventilation, in severly disabled patients.

Spinal muscular atrophy (SMA) is a genetic neurodegenerative disorder leading to immobilization and premature death. Currently, three alternative therapeutic options are available. Therefore, biomarkers that might reflect or predict the clinical course of the individual patient with treatment are of great potential use. Currently, the antisense oligonucleotide nusinersen is the prevalent and longest validated therapy for SMA. We analysed CSF candidate biomarkers for degenerative CNS processes (namely phosphorylated heavy chain (pNf‐H), light‐chain neurofilaments (NfL), total tau protein (T‐Tau), neurogranin, β‐secretase BACE‐1 and alpha‐synuclein) in 193 CSF samples of 44 paediatric SMA types 1, 2 and 3 patients before and under nusinersen treatment and related them to standardized clinical outcome scores in a single‐centre pilot study. pNf‐H and NfL correlated with disease severity and activity, emphasizing their relevance as marker of neuronal loss and clinical outcome. T‐Tau was significantly correlated with motor function scores in SMA type 1 making it an interesting marker for treatment response. Additionally, baseline T‐Tau levels were elevated in most SMA patients possibly reflecting the extension of neuronal degeneration in paediatric‐onset SMA. Further investigations of these CSF proteins might be beneficial for paediatric SMA subtypes and treatment modalities as an indicator for clinical outcome and should be analysed in larger cohorts.

Neuronal ceroid lipofuscinosis type 2 (CLN2 disease, OMIM 204500) is a rare autosomal-recessive lysosomal storage disorder. It is one of the most common neurodegenerative disorders in childhood. Symptoms include epilepsy, rapid motor and language regression, dementia, visual loss, and a complex movement disorder in later stages of the disease. We report on two children with genetically confirmed late-infantile CLN2 disease who developed a severe exacerbation of their complex movement disorder leading to hyperthermia, hyper-CK-emia and decreased level of consciousness over several weeks despite different therapeutic approaches. Both patients were on long-term antiepileptic treatment with valproate and only after the withdrawal of valproate, the movement disorder disappeared and level of consciousness improved. These observations emphasize that valproate has to be considered as a possible risk factor in patients in later stages of late-infantile CLN2 disease who develop a rapidly progressive complex movement disorder. ^* The authors Jessika Johannsen and Miriam Nickel contributed equally to the article.