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Auditory brainstem response in the identification of cochlear synaptopathy in aged rodents: a systematic review with meta-analysis.

PURPOSE: This systematic review and meta-analysis evaluated the diagnostic performance of auditory brainstem response (ABR) for identifying age-related cochlear synaptopathies in rodents. METHOD: Following PRISMA guidelines, searches were conducted in PubMed/MEDLINE, Cochrane Library, Scopus, Embase, Web of Science, SciELO, LILACS, and gray literature. Studies evaluating CS in naturally aged rodents using short-latency auditory evoked potentials (AEPs) were included. Study selection, data extraction, risk-of-bias (JBI Critical Appraisal Checklist for Analytical Cross-Sectional Studies), and certainty of the evidence (GRADE® system) assessment were conducted independently by two reviewers. Meta-analyses were performed using a random-effects model, with standardized mean differences and 95% confidence intervals. ABR wave I amplitudes were analyzed for click (80 and 90 dB SPL) and tone-burst stimuli stratified by frequency. RESULTS: Among 3,008 identified records, 12 studies were included in the review and five in the meta-analysis. All included studies used ABR measures to investigate CS, with wave I amplitude being the most frequently evaluated biomarker. Meta-analysis demonstrated a significant reduction in ABR wave I amplitude in aged rodents compared with young controls for both click- and tone-burst-evoked responses. Tone-burst ABR showed no significant differences among the evaluated frequencies. These findings should be interpreted with caution due to the limited number of studies and the methodological heterogeneity, which may have reduced statistical power and comparability. CONCLUSIONS: The evidence supports ABR wave I amplitude as a sensitive electrophysiological marker of age-related CS in rodents. Nevertheless, further studies with standardized protocols are needed to strengthen its diagnostic utility and improve comparability across studies.

Animals

AAV-mediated CBLN1 replacement rescues hereditary ataxia caused by bi-allelic CBLN1 variants.

Cbln1 is a secreted synaptic organizer required for parallel fiber-Purkinje cell (PF-PC) synapse integrity, climbing fiber (CF) refinement, and cerebellar motor learning but has not previously been implicated in human disease. We identified bi-allelic CBLN1 missense variants (A63P and Y112C) in two unrelated families with early-onset cerebellar ataxia accompanied by oculomotor abnormalities, cerebellar atrophy, and variable cognitive delay. In heterologous cells, both variants showed reduced steady-state protein abundance, impaired maturation through the early secretory pathway, and little or no detectable secretion, resulting in markedly reduced extracellular CBLN1 availability. Consistently, cerebellar granule cells expressing CBLN1-Y112C failed to induce excitatory synapses onto glutamate receptor δ2 (GluD2)-expressing cells in vitro. A knockin mouse harboring Y112C lacked synaptic Cbln1 and recapitulated key features of Cbln1 deficiency, including disrupted PF-PC synapse organization, persistent CF multi-innervation, impaired PF-PC transmission, and long-term depression, and deficits in motor coordination and oculomotor learning. Notably, systemic delivery of an astrocyte-targeted adeno-associated virus expressing wild-type CBLN1 in adult mutant mice restored synaptic CBLN1 localization, cerebellar synaptic function, plasticity, and behavior. These findings establish CBLN1 deficiency as a cause of hereditary ataxia and identify extracellular CBLN1 replacement as a therapeutic strategy for a reversible cerebellar synaptopathy.

CBLN1

Intellectual disability, neuroregression and adult-onset progressive dystonia due to a DLG4 pathogenic variant.

We report a 34-year-old male with childhood developmental delay, severe intellectual disability in adulthood, episodes of agitation with a previous diagnosis of schizoaffective disorder and adult-onset cognitive regression who developed progressive generalised dystonia due to a de novo DLG4 pathogenic loss-of-function variant. This case expands the phenotypic spectrum of recognised movement disorder manifestations associated with DLG4-related synaptopathy.

Humans

Unraveling the complex genetic landscape of OTOF-related hearing loss: a deep dive into cryptic variants and haplotype phasing.

BACKGROUND: Pathogenic variants in OTOF are a major cause of auditory synaptopathy. However, challenges remain in interpreting OTOF variants, including difficulties in confirming haplotype phasing using traditional short-read sequencing (SRS) due to the large gene size, the potential incomplete penetrance of certain variants, and difficulties in assessing variants at non-canonical splice sites. This study aims to revisit the genetic landscape of OTOF variants in a Taiwanese non-syndromic auditory neuropathy spectrum disorder (ANSD) cohort using a combination of sequencing technologies, predictive tools, and experimental validations. METHODS: We performed SRS to analyze OTOF variants in 65 unrelated Taiwanese patients diagnosed with non-syndromic ANSD, complemented by long-read sequencing (LRS) for haplotype phasing. A prediction-to-validation pipeline was implemented to assess the pathogenicity of cryptic variants using SpliceAI software and minigene assays. RESULTS: Biallelic pathogenic OTOF variants were identified in 33 patients (50.8%), while monoallelic variants were found in five patients. Three novel variants, c.3864G > A (p.Ala1288 =), c.4501G > A (p.Ala1501Thr), and c.5813 + 2T > C, were detected. The pathogenicity of two non-canonical mis-splicing variants, c.3894 + 5G > C and c.3864G > A (p.Ala1288 =), was confirmed by minigene assays. LRS-based haplotype phasing revealed that the common missense variant c.5098G > C (p.Glu1700Gln) and the novel variant c.5975A > G (p.Lys1992Arg) are in cis and form a founder pathogenic allele in the Taiwanese population. CONCLUSIONS: Our study highlights the genetic heterogeneity of DFNB9 and emphasizes the importance of population-specific variant interpretation. The integration of advanced sequencing technologies, predictive algorithms, and functional validation assays will improve the accuracy of molecular diagnosis and inform personalized treatment strategies for individuals with DFNB9.

Humans