Background:Disorders affecting the spinal cord (myelopathies) can cause severe disability. Despite diagnostic advances, approximately 12-18% of myelopathy cases continue to elude an etiological diagnosis, hampering effective treatment. Methods:This retrospective, multicenter, tertiary care cohort study conducted from 2014 to 2025 evaluated archived biofluids from patients with IM, known autoimmune myelitis, or other neurological diseases (ONDs). Proteome-wide phage display was used to discover novel autoantibodies. Targeted immunoassays were used to screen for a candidate autoantibody. Downstream metabolites were measured in the cerebrospinal fluid (CSF). Results:Autoantibodies targeting the transcobalamin receptor (CD320) responsible for cellular transport of vitamin B12 were identified in 18 out of 32 IM patients (56%) in a discovery cohort. Bioactive B12 concentration was decreased in the CSF of anti-CD320 positive patients compared to OND controls ( P = 0.0273), indicative of autoimmune B12 central deficiency (ABCD). Compared to anti-CD320 negative IM cases, anti-CD320 positive IM cases demonstrated a higher frequency of subacute time course (56% vs 7%, P = 0.008), normal CSF profile (83% vs 50%, P = 0.044), and dorsolateral spinal cord abnormalities on magnetic resonance imaging (MRI) (61% vs 7%, P = 0.003). In two independent validation cohorts comprising 94 and 25 patients with IM, anti-CD320 was detected in 43 (46%) and 12 (48%) patients, respectively. Comorbid anti-CD320 was detected in a smaller proportion of patients with other known autoimmune etiologies of myelopathy. Five anti-CD320 positive IM patients received B12 supplementation with or without concurrent immunosuppression, and four out of five clinically improved. Conclusions:ABCD is associated with a substantial proportion of IM. Screening for anti-CD320 followed by metabolic confirmation of a CNS-restricted B12 deficiency may be considered in the diagnostic evaluation of myelopathy.

Due to shared ß-hexosamindase A deficiencies and significant clinical overlap, the predominating subtypes of late-onset GM2 gangliosidosis, late-onset Tay-Sachs (LOTS) and late-onset Sandhoff disease (LOSD) have been considered essentially indistinguishable. However, growing evidence supports several distinctions between the two entities. We highlight these distinctions through the cross-sectional evaluation of 27 (21 LOTS and 6 LOSD) late-onset GM2 gangliosidosis participants. Study protocol included physical examinations, assessments of gait, balance, muscle strength, ataxia, and nerve conduction velocities, and brain magnetic resonance imaging. Lower limb weakness and later development of upper limb weakness was highly prevalent in both diseases. Accompanying gait disturbances, balance issues, and dysmetria were also prevalent in both cohorts. Strength evaluations showed weakness in both the LOTS and LOSD cohorts compared to controls primarily impacting extensor muscles. In contrast, BARS scores for dysarthria and oculomotor dysfunction were present and heterogenous in LOTS participants and absent in LOSD participants. Twenty-four percent of LOTS participants and none of the LOSD participants had a history of neuropsychiatric symptoms. Cerebellar volume including lobules V and VI were lower in LOTS compared to LOSD and normative data. However, severe length-dependent sensory neuropathy was present in all LOSD participants but not in LOTS participants. The finding of lower cerebellar volume in LOTS suggests the distinctive features of the LOTS phenotype are related to cerebellar dysfunction. However, the cause of the phenotypic differences between LOTS and LOSD remains a mystery, and the molecular and biochemical basis for the dichotomy requires further investigation.

The hereditary cerebellar ataxias are a clinically and genetically heterogeneous group of disorders characterized by progressive cerebellar degeneration leading to incoordination of gait, speech, limb, and eye movements. Hundreds of genes encoding diverse proteins underlie this family of degenerative disorders that may exhibit autosomal dominant, recessive, mitochondrial, or X-linked inheritance. Variations in clinical presentation, such as age of onset and severity, are typical of these disorders and are attributed to other genetic effects, notably repeat expansion instability. In this observational study, we evaluated 45 individuals in a 5-generation kindred exhibiting features of progressive ataxia and cognitive impairment with wide-ranging ages of onset, intergenerational anticipation, diverse clinical features, and male infertility. The variant (m.9035 T > C) in the gene MT-ATP6 was detected in all affected individuals, and the age of onset from early childhood to the 8th decade was inversely correlated with heteroplasmy levels. Neuropsychological evaluation of affected individuals demonstrated low average/borderline overall intellectual ability and weaknesses in working memory, executive function, memory, and fine motor skills. Affected males had testicular atrophy and azoospermia. Postmortem examination revealed widespread cerebellar Purkinje cell loss. Testicular biopsy from one sterile male demonstrated a complete absence of germ cells and progenitors. This study expands the phenotypic spectrum of MT-ATP6 to include azoospermia in affected males with cerebellar ataxia. Those with low levels of heteroplasmy had mild adult-onset ataxia reminiscent of many forms of SCA. Those with high levels of heteroplasmy had early onset and suffered from the full complement of ataxia, mild cognitive impairment, and in males’ azoospermia.

Objectives:Cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), the most common inherited cerebral small vessel disease (cSVD), involves NOTCH3-mediated microvascular pathology. As retinal health remains underexplored, serial ultra-widefield fluorescein angiography (UW-FA) was used to characterize dynamic vessel dysfunction. Methods:UW-FA was performed at baseline and after 13.9 ± 4.5 months. Retinal vessel permeability, blood flow, and perfusion across macular, mid-peripheral, and far-peripheral zones were quantified. Aberrant pixels exceeded healthy volunteer (HV) thresholds. Group differences, longitudinal changes, NOTCH3 variant loci, and stroke-age associations were analyzed. Results:Nineteen patients with genetically confirmed CADASIL (mean age 48.4 years; 52.6% female) and 9 matched HVs (mean age 44.3 years, 55.6% female) were included. Baseline far-peripheral permeability was higher in the CADASIL group vs HVs (p = 0.03; r = 0.41). At follow-up, mid-peripheral permeability increased (p = 0.003; r = 0.56) and far-peripheral permeability remained elevated (p = 0.0007; r = 0.64) in patients with CADASIL. Longitudinal analysis showed reduced blood flow and perfusion in the macula and mid-periphery and increased midperipheral permeability (all statistically significant with substantial effect sizes). Neither genotype nor stroke-onset age predicted alterations. Discussion:Serial UW-FA scans detect progressive, region-specific retinal vessel dysfunction in a modest-sized cohort with CADASIL, potentially serving as a surrogate marker for cSVD progression.

The vast majority of individuals with autosomal recessive (AR) conditions demonstrate biparental inheritance of the disease-causing alleles; however, de novo variants also contribute to AR disease. This report represents the largest cohort to-date of rare AR conditions in which one of the disease-causing alleles was inherited and one occurred de novo. Clinical and research staff at Stanford University, clinical sites of the Undiagnosed Diseases Network (UDN) and Genomics Research to Elucidate the Genetics of Rare diseases (GREGoR) Consortium, and a large clinical genetic testing laboratory were contacted to identify cases of an AR diagnosis resulting from an inherited and de novo disease-causing variant in trans. Fifteen cases of AR conditions caused by one inherited and one de novo variant in a gene consistent with the clinical phenotype were identified; all had undergone trio exome or genome sequencing with genetic confirmation of reported relationships. Variants were confirmed to be in trans in eight of the 15 cases. The de novo variant was confirmed (n = 7) or presumed (n = 7) to have arisen on the paternal allele in 14/15 (93%) of cases. Phenotypic and/or molecular evidence of an AR condition should prompt parental segregation analysis to inform diagnosis, recurrence risks, and variant classification. Additional studies are needed to determine the incidence of this phenomenon given the implications for the interpretation of genetic testing and counseling for AR conditions.

OBJECTIVE:Despite functional mobility losses being the primary complaint in late-onset Tay-Sachs and Sandhoff disease (LOTS-SD), a quantitative understanding of neuromuscular degeneration is lacking. Our aim is to quantitatively characterize muscle degeneration using ultrasound measures of muscle thickness, echogenicity, and stiffness. Additionally, we investigate if elbow and knee extensors are preferentially affected in LOTS-SD. METHODS:Twenty patients diagnosed with LOTS-SD and 20 matched controls (age, sex, BMI) participated. Muscle thickness, echogenicity, and stiffness were quantified and compared across cohorts in the triceps, biceps, rectus femoris (RF) and semimembranosus (SM). For each measurement, the extensor-to-flexor and lower-to-upper-limb muscle ratios (triceps-to-biceps, RF-to-SM, and RF-to-triceps) were also compared. RESULTS:Patients with LOTS-SD demonstrated triceps, RF, and SM atrophy (24-47%), increased RF and triceps echogenicity (21-36%), and increased RF stiffness (10%). The triceps-to-biceps and RF-to-SM thickness ratios were decreased (-42%, -25%) and increased for echogenicity (32%, 35%). Notably, for the RF-to-triceps ratio, only the stiffness ratio was elevated (18%) in patients. CONCLUSION:Neuromuscular ultrasound confirmed patterns of preferential elbow/knee extensors degeneration in LOTS-SD. While lower (RF) and upper limb (triceps) atrophy appeared proportionate, elevated RF stiffness indicates potentially varied degeneration pathways for these two muscles. SIGNIFICANCE:These findings highlight neuromuscular ultrasound's potential role in disease monitoring and differential diagnosis.

Purpose:To explore the phenotypic spectrum and genetic etiologies of Moebius Syndrome (MBS), a rare neurological disorder defined by congenital, nonprogressive facial weakness and limitations in ocular abduction. Methods:We applied strict diagnostic criteria and conducted clinical phenotyping of 149 individuals with MBS. Subsequently, we performed exome and/or genome sequencing on 67 of these individuals and 117 unaffected family members. Results:All 149 individuals had sporadic MBS, with no recurrence within or across generations. Common co-occurring phenotypes included tongue hypoplasia (81.9%), micrognathia (66.4%), congenital talipes equinovarus (42.3%), major limb anomalies (31.5%), intellectual disability (30.9%), sleep difficulties (22.8%), and Poland anomaly (14.1%). Filtering for rare de novo or autosomal recessive single-nucleotide, insertion/deletion, and structural variants in the sequenced cohort yielded 173 single-nucleotide variant/indels in 113 genes. Although we prioritized 7 candidate genes with de novo variants and 5 with biallelic variants, no compelling recurrently mutated genes were identified. Similarly, we found no convincing variants in 2 putative genes previously implicated in MBS: PLXND1 (HGNC:9107) and REV3L (HGNC:9968). Conclusion:We did not identify a strong or unifying germline genetic etiology for MBS. Future studies may explore alternative causes, including environmental exposures, somatic variants, and/or complex inheritance patterns affecting brainstem and organ embryogenesis.

BACKGROUND:Primary brain calcifications are observed in several inherited diseases due to different pathogenic mechanisms, including the disruption of the neurovascular unit, mitochondrial dysfunction, and impaired nucleic acid metabolism. OBJECTIVE:The aim of the study was to identify a novel genetic cause of brain calcifications in genetically unresolved cases. METHODS:Exome sequencing data from two unrelated Pakistani patients with generalized dystonia and primary brain calcifications were analyzed. The best candidate gene (ie, RRP12) was then investigated in two large cohorts of patients with brain calcifications from France (n = 111) and China (n = 543). RRP12 loss-of-function phenotype was explored through Western blot and immunocytofluorescence studies on patient-derived fibroblasts and in a knockdown zebrafish model. RESULTS:A combined approach of exome sequencing and homozygosity mapping allowed the prioritization of a rare homozygous variant in RRP12 (c.1558C>T, p.R520C) in two apparently unrelated Pakistani patients from consanguineous families, presenting with infantile-onset generalized dystonia, spasticity, and widespread brain calcifications. Screening of two large cohorts of patients with unresolved brain calcifications revealed two affected French siblings and one unrelated Chinese individual, each carrying rare, biallelic, missense variants in the RRP12 gene (c.1429G>A, p.E477K and c.2634T>G, p.F878L, respectively). Molecular studies revealed a significant reduction in RRP12 protein and abnormal nucleolar morphology in patient'derived fibroblasts. Consistent with its essential role in RNA metabolism, rrp12 knockdown in zebrafish caused severe developmental delay, crimping, and early lethality. CONCLUSIONS:RRP12 is a novel candidate gene for autosomal recessive brain calcifications, possibly associated with a wide clinical spectrum ranging from early-onset severe forms to adult-onset paucisymptomatic presentations. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Seventy-five unique variants in the KCNMA1 gene have been identified from individuals with neurological disorders. However, variant pathogenicity and evidence for disease causality are lacking in most cases. In this study, the KCNMA1 variants N999S and E656A (rs886039469 and rs149000684, respectively) were investigated from two individuals presenting with neurological disorders. N999S was previously shown to produce strong gain-of-function (GOF) changes in homomeric BK channel properties in vitro and is found as a heterozygous allele associated with epilepsy and paroxysmal dyskinesia in humans. Although its pathogenicity has been demonstrated in heterozygous animal models, the GOF classification for N999S has not been validated in a heterozygous patient-derived tissue. Conversely, the GOF pathogenicity for E656A is based solely on homomeric channels expressed in vitro and is inconclusive. For either variant, the properties of single heterozygous channels and allele expression is unknown. In this study, we profiled the wild-type and mutant KCNMA1 transcripts from primary human skin fibroblasts of heterozygous patients and unaffected controls and performed patch-clamp electrophysiology to characterize endogenous BK channel current properties. GOF gating was observed in single BK channel recordings from both channel types. Fibroblasts from the individual harboring the E656A variant showed decreases in the number of BK channels detected and E656A-containing transcripts compared to controls. These results show that single BK channels can be reliably detected in primary fibroblasts obtained from human skin biopsies, suggesting their utility for establishing variant pathogenicity, and reveal the BK channel expression and functional changes associated with two heterozygous patient genotypes.

Leukoencephalopathy with brain calcifications and cysts (LCC), also known as Labrune Syndrome, is a rare cerebral microangiopathy caused by biallelic variants in the SNORD118 gene, which encodes the small nucleolar RNA (snoRNA) U8, a critical component of ribosome biogenesis. We present LCC cases with unusually protracted diagnostic trajectories. Case 1 had symptom onset in adolescence but remained undiagnosed until adulthood, while Case 2 had a transient occurrence of seizures in childhood and developed disabling motor symptoms in adulthood. Both were initially misdiagnosed—one with neurocysticercosis, the other with Fahr’s disease and multiple sclerosis—leading to inappropriate treatments. On evaluation, both probands exhibited asymmetrical spasticity with upper motor neuron weakness and pseudobulbar features. Genetic analyses confirmed compound heterozygous SNORD118 variants, including a rare upstream non-coding change (n.–6G>A). Neuroimaging revealed extensive leukoencephalopathy and calcifications, with cysts present in only one case. Notably, the severity of neuroimaging abnormalities contrasted with the milder or delayed clinical manifestations, underscoring phenotypic variability and the insidious nature of the disease process. These cases expand the clinical and imaging spectrum of SNORD118-related LCC, highlight diagnostic pitfalls and demonstrate challenges in variant detection due to incomplete coverage or reporting of non-coding regions in exome and genome sequencing. Greater awareness of LCC and improved interrogation of non-coding RNAs through clinical sequencing are essential for timely and accurate diagnosis.

GM2 gangliosidosis is lysosomal storage disorder caused by deficiency of the heterodimeric enzyme β-hexosaminidase A. Tay–Sachs disease is caused by variants in HEXA encoding the α-subunit and Sandhoff disease is caused by variants in HEXB encoding the β-subunit. Due to shared clinical and biochemical findings, the two have been considered indistinguishable. We applied T1-weighted volumetric analysis, diffusion tensor imaging (DTI), and correlational fiber tractography to assess phenotypic differences in these two diseases. 51 T1-weighted and 40 DTI scans from 19 Late-Onset GM2 patients with either late-onset Sandhoff disease (LOSD), or late-onset Tay–Sachs (LOTS) were included and compared to 1033 neurotypical control volumetric MRI scans. LOTS patients had significantly smaller cerebellum volume compared to neurotypical controls (p < 0.0001) and LOSD patients (p < 0.0001). There was no statistical difference for the volume of any structure between LOSD and neurotypical controls. DTI analysis showed LOTS patients had higher mean diffusivity (MD) in the left cerebellum (p = 0.003703), right cerebellum (p = 0.003435), superior cerebellar peduncle (p = 0.007332), and vermis (p = 0.01007) compared to LOSD. LOTS patients had lower fractional anisotropy (FA) in the left cerebellum (p = 0.005537), right cerebellum (p = 0.01905), SCP (p = 0.02844), and vermis (p = 0.02469) when compared to LOSD. Correlational fiber tractography identified fiber tracts in cerebellar pathways with higher FA and lower MD in LOSD patients compared to LOTS patients. Our study shows neurobiologic differences between these two related disorders. To our knowledge, this is the first study using correlational tractography in a lysosomal storage disorder. This result indicates a greater burden of cerebellar pathology in LOTS patients compared with LOSD patients.

The National Institute of Health (NIH) Undiagnosed Diseases Program (UDP) is an NIH project with the goal of providing both a comprehensive diagnosis and a better understanding of the many mechanisms of disease for patients with rare and undiagnosed conditions. Patients accepted to the program receive a careful review of their medical records and a tailored inpatient evaluation at the NIH Clinical Center in Bethesda, MD. For the pediatric population, systematic neurodevelopmental phenotypic evaluations are included. Here we report neurodevelopmental phenotyping data on pediatric participants enrolled in the NIH UDP from 2009 to 2019, with genetic findings reported through 2025. Results for 219 pediatric participants included a high rate of intellectual disability, with 27% of the sample in the severe-to-profound range. The phenotype often included multisystemic involvement, with motor impairments as well as vision and hearing concerns. For the 46% for whom a genetic diagnosis was made, there was greater impairment, including more severe intellectual disability and more frequent motor impairments as well as minimal verbal status. This study documented that severe neurodevelopmental impairments are frequently present in the unique pediatric undiagnosed patients enrolled in NIH UDP; the diagnosis of a genetic condition was associated with greater impairment.

RAB3A encodes a small GTP-binding protein that is abundant in brain synaptic vesicles and crucial for the release of neurotransmitters and synaptic plasticity. Here, we identified RAB3A as a candidate gene for autosomal dominant cerebellar ataxia by two independent approaches: linkage in a large dominant ataxia family and, in parallel, an untargeted computational genetic association approach, analysing the 100 000 Genomes Project datasets. To validate the role of RAB3A in ataxia, we next screened large rare disease databases for rare heterozygous RAB3A variants in probands with ataxia features. In total, we identified 18 individuals from 10 unrelated families all sharing a cerebellar ataxia phenotype. Notably, 9 of the 10 families carried a recurrent variant in RAB3A, p.Arg83Trp, including one de novo occurrence. In addition, our screening revealed three families with a neurodevelopmental phenotype and three unique RAB3A variants, which were either de novo or loss-of-function variants. In line with the different RAB3A variant types, protein domains and predicted functional consequences, a comprehensive set of complementary methods was used to characterize the identified variants functionally. As expected, GTPase-activating protein (GAP)-dependent GTP hydrolysis was reduced for those two missense variants located in the GAP-binding domain of RAB3A (Arg83Trp and Tyr91Cys). In a Drosophila Rab3 loss-of-function model, these two missense variants also failed to rescue a synaptic phenotype. Overexpression of Rab3 variants in Drosophila wild-type background did not cause an obvious phenotype, making a dominant negative effect of these variants unlikely. Lastly, exploring interactors of RAB3A variants by using co-immunoprecipitation and mass spectrometry showed differential changes in variant-specific interactions with known RAB3A key regulatory and effector proteins. In sum, our results establish RAB3A as a neurological disease gene. It represents an autosomal dominant gene for cerebellar ataxia with different variants associated with disease, including the frequent reoccurring variant p.Arg83Trp. Our study sheds light on the variant-specific interactome of RAB3A. Finally, we suggest an association of RAB3A with a neurodevelopmental phenotype, as reported for variants in several RAB3A interaction partners and as seen in Rab3A-deficent mice, although this possible association warrants further investigation by future studies.

INTRODUCTION:The clinical, radiological, and pathological features have not been well documented for the recently discovered autosomal-dominant vacuolar tauopathy (VT) harboring the Valosin-containing protein (VCP) p.Asp395Gly variant. METHODS:We investigated the clinical, neuropsychological, physiological, laboratory, and radiological data and neuropathological findings in five symptomatic VT cases who met the diagnostic criteria for frontotemporal dementia (FTD). Radiological data were also collected from two pre-symptomatic carriers. RESULTS:All participants had heterozygous c.1184A > G, p.Asp395Gly in VCP. All symptomatic cases exhibited cognitive, behavioral, and/or language dysfunction indicative of FTD in their 30s to 50s. Neuroimaging studies revealed marked bilateral frontal neurodegeneration and occipital lobar diffusion abnormalities. Post mortem examination of three cases and brain biopsy of one case revealed abundant three- and four-repeat tau deposition and neocortical microvacuolization. Radiological changes were not evident in two pre-symptomatic carriers in their 20s. DISCUSSION:This study reveals distinct clinical-radiological-pathological correlations in VT, expanding the spectrum of early-onset frontotemporal lobar degeneration (FTLD). HIGHLIGHTS:We characterized the clinical, radiological, and pathological features of vacuolar tauopathy (VT). Five VT cases exhibited a behavioral syndrome, often with aphasic features, with marked frontal lobar atrophy and hypometabolism. Magnetic resonance imaging (MRI) of VT cases revealed occipital lobar diffusion abnormalities. Diffuse neurofibrillary tangles (NFTs) and microvacuolization were observed in the neocortex, with an inverse distribution.