Biallelic loss-of-function variants in NRROS (Negative regulator of reactive oxygen species, previously LRRC33) cause a progressive neurodegenerative disorder characterized by early-onset seizures with brain calcifications. To date, 16 affected individuals from 13 unrelated families have been reported for this condition. We describe two siblings from a consanguineous family with this disorder, carrying a homozygous NRROS missense variant (c.1222A>C, p.(Asn408His), NM_198565.3). The mutational spectrum of NRROS disorder is characterized primarily by loss-of-function variants, with only four missense variants identified in affected individuals to date p.(Leu10Pro), p.(Leu62Pro), p.(Leu86Pro), and p.(Asn408His). We characterized these missense variants using silico predictions, molecular modelling and in-vitro cellular localization studies. In silico tools predict that p.(Leu10Pro) alters signal peptide cleavage, while p.(Asn408His) impedes N-linked glycosylation. Molecular modelling suggests that p.(Leu62Pro) and p.(Leu86Pro) variants may destabilize NRROS structure, while p.(Asn408His) interferes with NRROS glycosylation. In-vitro studies overexpressing HA-tagged NRROS wild type and missense variants in HEK293 cells showed altered subcellular distribution patterns for the variant proteins. In summary, we report a homozygous missense variant in NRROS associated with severe infantile epilepsy syndrome with intracranial calcifications, and neurodegeneration.

Biallelic loss-of-function variants in NRROS cause SENEBAC. Here, we report two affected siblings from a consanguineous family with a homozygous missense variant in NRROS. Preliminary functional assays in HEK293 cells for all the pathogenic NRROS missense variants, including the newly identified one, showed cellular mislocalization compared to the wild-type protein.

Rare genetic variants in the glycine receptor (GlyR) α2 subunit gene ( GLRA2 ) are associated with autism spectrum disorder, developmental delay, and intellectual disability, often accompanied by microcephaly, language delay or epilepsy. We report detailed structure-function analyses of nine previously uncharacterised GlyR α2 missense variants, including a novel de novo change (p.S285P) linked to epileptic encephalopathy. Using molecular modelling/dynamics simulations, electrophysiology, and immunocytochemistry, we assessed effects of GlyR α2 variants on agonist potency, efficacy, channel gating, and cell-surface trafficking. Five missense variants caused a partial loss-of-function via reduced glycine potency (p.F20S, p.A261T, p.R418Q), reduced glycine efficacy (p.F20S), or faster channel deactivation (p.R323C, p.P369T). By contrast, p.R225C abolished cell-surface expression resulting in a complete loss-of-function . The p.A261T variant also significantly reduced picrotoxin binding, resolving ambiguity in GlyR-PTX interaction models. Additional variants showed an alteration-of-function (p.I232M) or a gain-of-function (p.S285P), combining reduced glycine efficacy with increased potency and spontaneous leak currents. Two variants within the intracellular M3-M4 domain (p.R323C and p.P369T) had enhanced channel deactivation consistent with a loss-of-function , while p.P373L showed no detectable functional deficit. These findings expand the clinical and mechanistic spectrum of GlyR α2 variants, identify a key determinant of picrotoxin binding, and highlight unresolved roles of intracellular protein-protein interaction motifs in GlyR α2 function.

Pentameric glycine receptors (GlyRs) are key modulators of inhibitory neurotransmission, yet visualization of their activity across neuronal compartments has remained a challenge. Current methods that employ intracellularly tagged genetically encoded fluorescent proteins are prone to artefacts, as the tags can disrupt protein interactions that regulate receptor trafficking and positioning within the cell. We developed a novel, genetically encoded GlyRα2 activity reporter by fusing a chloride-sensitive fluorescent protein, mClYFP, to the extracellular N-terminus of GlyRα2. This chimeric receptor allows real-time nanoscopic visualization of the receptor and glycine-induced chloride concentration changes using total internal reflection fluorescence microscopy and ratio image analysis. Simultaneous electrophysiological and fluorescence measurements validated the functionality of both the ion channel and mClYFP components of our GlyRα2 activity reporter. The GlyRα2 ion channel characteristics are preserved, and the extracellular mClYFP tag reports chloride concentration changes in the physiological range. Therefore, mClYFP-GlyRα2 allowed us to detect receptor activity of chloride-permeable ionotropic receptors. In addition, we demonstrate that mClYFP-GlyRα2 can be effectively expressed in physiologically relevant striatal neurons. We present an extracellularly located, receptor-specific sensor that enables surface-accessible tracking of chloride ion dynamics in live cells. Our approach enables spatially resolved, non-invasive monitoring of chloride permeable receptor signaling, offering a powerful tool to investigate pentameric receptor function at the nanoscale.

The honeybee mite, Varroa destructor, finally breached Australia’s biosecurity defences four years ago, and is here to stay. Even more concerning, our standard treatments – such as specialised pesticides – are already failing.

What does this mean for Australians, and what can we do about it?

Roughly the size of a pinhead, the parasitic mite is regarded as the most destructive pest of honeybees worldwide. It feeds on bees, weakening colonies and causing their collapse.

For decades, Australia was the only continent free of the mite. That changed in 2022, when Varroa was detected in sentinel hives at the Port of Newcastle, New South Wales.

An ambitious eradication campaign was launched, but abandoned by 2023. Today, Varroa is established across much of Australia’s eastern and southern states. The focus has shifted from eradication to management, and we now face a new threat – treatment-resistant mites.

Objective

Landau–Kleffner syndrome (LKS), is a rare, poorly-understood epileptic encephalopathy with spike–wave activation in sleep associated with mutations in GRIN2A, encoding the N-Methyl-D-Aspartate receptor (NMDAR) GluN2A subunit. Physicians rely on empirical treatments, with scarce information on treatment efficacy and outcomes. This study aims to improve the understanding and clinical management of LKS.

Methods

Fifty-two patients with LKS were recruited via one quaternary referral center. Case-notes review delineated clinical features, long-term outcomes, and prognostic factors. Generalized estimating equations were used to determine the longitudinal association among electroencephalogram abnormalities, steroid therapy, and neuropsychological findings. After genetic screening, the impact of identified GRIN2A missense variants on NMDAR function was assessed using homology modeling, cell-surface trafficking assays, and electrophysiology in artificial synapses. Whole exome/genome sequencing was performed on GRIN2A-negative patients to identify novel gene associations.

Results

LKS is complex with significant clinical and genetic heterogeneity. Besides speech and language impairment, many patients had other co-morbidities and almost half have long-term disability. Early age at disease onset was associated with worse outcomes. There was no reliable correlation between electroencephalogram findings and developmental scores. Steroid therapy improved language outcomes independently of electroencephalogram findings. GRIN2A mutations were identified in 15.5% of the cohort. Likely pathogenic variants in GABBR2, SCN1A, TRPC1, ERRFI1, CTXN3, IRX6, and IQCA1 were identified in 7 GRIN2A-negative individuals.

Interpretation

For LKS, early intervention is important for long-term outcomes. Furthermore, management should not be based solely on electroencephalogram findings. Genetic and functional investigations offer insights into disease pathophysiology and facilitate development of future targeted therapies. ANN NEUROL 2025