Re-evaluation of missense variant classifications in NF2.

Missense variants in the NF2 gene result in variable NF2 disease presentation. Clinical classification of missense variants often represents a challenge, due to lack of evidence for pathogenicity and function. This study provides a summary of NF2 missense variants, with variant classifications based on currently available evidence. NF2 missense variants were collated from pathology-associated databases and existing literature. Association for Clinical Genomic Sciences Best Practice Guidelines (2020) were followed in the application of evidence for variant interpretation and classification. The majority of NF2 missense variants remain classified as variants of uncertain significance. However, NF2 missense variants identified in gnomAD occurred at a consistent rate across the gene, while variants compiled from pathology-associated databases displayed differing rates of variation by exon of NF2. The highest rate of NF2 disease-associated variants was observed in exon 7, while lower rates were observed toward the C-terminus of the NF2 protein, merlin. Further phenotypic information associated with variants, alongside variant-specific functional analysis, is necessary for more definitive variant interpretation. Our data identified differences in frequency of NF2 missense variants by exon between gnomAD population data and NF2 disease-associated variants, suggesting a potential genotype-phenotype correlation; further work is necessary to substantiate this.

The management of symptomatic hyperostotic bilateral spheno-orbital meningiomas: patient series.

BACKGROUND: The occurrence of hyperostotic bilateral spheno-orbital meningiomas (BSOMs) is very rare. Patients present with bilateral symptoms and require bilateral treatment. This series describes 6 patients presenting to 2 UK neurosurgical units and includes a literature review. To the best of the authors' knowledge, this is the largest series documented. OBSERVATIONS: This is a retrospective review of patients with BSOMs presenting between 2006 and 2023. Six females, whose mean age was 43 (range: 36-64) years, presented with features of visual disturbance. Bilateral sphen-oorbital meningiomas were identified. All patients underwent bilateral staged resections. The patients had an initial improvement in their symptoms. Extensive genetic testing was performed in 4 patients, with no variants in the NF2, LZTR1, SMARCB1, SMARCE1, and SMARCA4 genes or other variants detected. The mean follow-up was 100.3 (range: 64-186) months. Sixty-seven percent of patients had good long-term visual acuity. The progression rate was 75% and was particularly aggressive in 1 patient. Four patients required radiation therapy, and 2 needed further surgery. LESSONS: Hyperostotic BSOMs are extensive, challenging tumors causing significant disability. They can recur, with significant patient impact. Multidisciplinary management and indefinite long-term follow-up are essential. The biology of these tumors remains unclear. As molecular testing expands, the understanding of BSOM oncogenesis and potential therapeutic targets is likely to improve.

Identification of a human synaptotagmin-1 mutation that perturbs synaptic vesicle cycling.

Synaptotagmin-1 (SYT1) is a calcium-binding synaptic vesicle protein that is required for both exocytosis and endocytosis. Here, we describe a human condition associated with a rare variant in SYT1. The individual harboring this variant presented with an early onset dyskinetic movement disorder, severe motor delay, and profound cognitive impairment. Structural MRI was normal, but EEG showed extensive neurophysiological disturbances that included the unusual features of low-frequency oscillatory bursts and enhanced paired-pulse depression of visual evoked potentials. Trio analysis of whole-exome sequence identified a de novo SYT1 missense variant (I368T). Expression of rat SYT1 containing the equivalent human variant in WT mouse primary hippocampal cultures revealed that the mutant form of SYT1 correctly localizes to nerve terminals and is expressed at levels that are approximately equal to levels of endogenous WT protein. The presence of the mutant SYT1 slowed synaptic vesicle fusion kinetics, a finding that agrees with the previously demonstrated role for I368 in calcium-dependent membrane penetration. Expression of the I368T variant also altered the kinetics of synaptic vesicle endocytosis. Together, the clinical features, electrophysiological phenotype, and in vitro neuronal phenotype associated with this dominant negative SYT1 mutation highlight presynaptic mechanisms that mediate human motor control and cognitive development.

Loss-of-function mutations in MICU1 cause a brain and muscle disorder linked to primary alterations in mitochondrial calcium signaling.

Mitochondrial Ca(2+) uptake has key roles in cell life and death. Physiological Ca(2+) signaling regulates aerobic metabolism, whereas pathological Ca(2+) overload triggers cell death. Mitochondrial Ca(2+) uptake is mediated by the Ca(2+) uniporter complex in the inner mitochondrial membrane, which comprises MCU, a Ca(2+)-selective ion channel, and its regulator, MICU1. Here we report mutations of MICU1 in individuals with a disease phenotype characterized by proximal myopathy, learning difficulties and a progressive extrapyramidal movement disorder. In fibroblasts from subjects with MICU1 mutations, agonist-induced mitochondrial Ca(2+) uptake at low cytosolic Ca(2+) concentrations was increased, and cytosolic Ca(2+) signals were reduced. Although resting mitochondrial membrane potential was unchanged in MICU1-deficient cells, the mitochondrial network was severely fragmented. Whereas the pathophysiology of muscular dystrophy and the core myopathies involves abnormal mitochondrial Ca(2+) handling, the phenotype associated with MICU1 deficiency is caused by a primary defect in mitochondrial Ca(2+) signaling, demonstrating the crucial role of mitochondrial Ca(2+) uptake in humans.