Structural interhemispheric connectivity defects in mouse models of BBSOAS: Insights from high spatial resolution 3D white matter tractography.

White matter (WM) tract formation and axonal pathfinding are major processes in brain development allowing to establish precise connections between targeted structures. Disruptions in axon pathfinding and connectivity impairments will lead to neural circuitry abnormalities, often associated with various neurodevelopmental disorders (NDDs). Among several neuroimaging methodologies, Diffusion Tensor Imaging (DTI) is a magnetic resonance imaging (MRI) technique that has the advantage of visualizing in 3D the WM tractography of the whole brain non-invasively. DTI is particularly valuable in unpinning structural tract connectivity defects of neural networks in NDDs. In this study, we used 3D DTI to unveil brain-specific tract defects in two mouse models lacking the Nr2f1 gene, which mutations in patients have been proven to cause an emerging NDD, called Bosch-Boonstra-Schaaf Optic Atrophy (BBSOAS). We aimed to investigate the impact of the lack of cortical Nr2f1 function on WM morphometry and tract microstructure quantifications. We found in both mutant mice partial loss of fibers and severe misrouting of the two major cortical commissural tracts, the corpus callosum, and the anterior commissure, as well as the two major hippocampal efferent tracts, the post-commissural fornix, and the ventral hippocampal commissure. DTI tract malformations were supported by 2D histology, 3D fluorescent imaging, and behavioral analyses. We propose that these interhemispheric connectivity impairments are consistent in explaining some cognitive defects described in BBSOAS patients, particularly altered information processing between the two brain hemispheres. Finally, our results highlight 3DDTI as a relevant neuroimaging modality that can provide appropriate morphometric biomarkers for further diagnosis of BBSOAS patients.

Variants in the WDR45 Gene Within the OPA-2 Locus Associate With Isolated X-Linked Optic Atrophy.

Purpose: To describe clinical and molecular findings of two families with X-linked optic atrophy and present two new pathogenic variants in the WDR45 gene. Methods: Case series and molecular analysis of two families of Jewish Ashkenazi descent with early onset bilateral optic atrophy. Whole-exome sequencing (WES) and bioinformatic analysis were performed, followed by Sanger sequencing and segregation analysis. Results: In both families, male siblings (three in family 1, two in family 2) had early-onset isolated bilateral optic atrophy. The sibling's healthy mother (and in the second family also one healthy sister) had a mild presentation, suggesting a carrier state and an X-linked inheritance pattern. All participants were otherwise healthy, apart from mild learning disabilities and autism spectrum disorder in two siblings of the second family. Variants in known optic atrophy genes were excluded. Analysis revealed a point variant in the WDR45 gene-a missense variant in the first family, NM_001029896.2:c.107C>A; NP_001025067.1:p.Pro36His (variant ID: 1704205), and a splice site variant in the second family, NM_001029896.2:c.236-1G>T; NP_009006.2:p.Val80Leu (variant ID: 1704204), located on Xp11.23 (OPA2 locus). Both variants are novel and predicted as pathogenic. In both families, the variant was seen with full segregation with the disease, occurring in all affected male participants and in one allele of the carrier females, as well as none of the healthy participants. Conclusions: Among two families with isolated X-linked optic atrophy, molecular analysis revealed novel variants in the WDR45 gene in full segregation with the disease. This gene resides within the OPA2 locus, previously described to associate with X-linked optic atrophy. Taken together, these findings suggest that certain pathogenic variants in the WDR45 gene are associated with isolated X-linked optic atrophy.

Infantile onset encephalomyopathy, retinopathy, optic atrophy, and mitochondrial DNA depletion associated with a novel pathogenic DHX16 variant.

We studied a patient with mitochondrial DNA depletion in skeletal muscle and a multiorgan phenotype, including fatal encephalomyopathy, retinopathy, optic atrophy, and sensorineural hearing loss. Instead of pathogenic variants in the mitochondrial maintenance genes, we identified previously unpublished variant in DHX16 gene, a de novo heterozygous c.1360C>T (p. Arg454Trp). Variants in DHX16 encoding for DEAH-box RNA helicase have previously been reported only in five patients with a phenotype called as neuromuscular oculoauditory syndrome including developmental delay, neuromuscular symptoms, and ocular or auditory defects with or without seizures. We performed functional studies on patient-derived fibroblasts and skeletal muscle revealing, that the DHX16 expression was decreased. Clinical features together with functional data suggest, that our patient's disease is associated with a novel pathogenic DHX16 variant, and mtDNA depletion could be a secondary manifestation of the disease.

Aldose reductase inhibition decelerates optic nerve degeneration by alleviating retinal microglia activation.

As part of the central nervous system (CNS), retinal ganglion cells (RGCs) and their axons are the only neurons in the retina that transmit visual signals from the eye to the brain via the optic nerve (ON). Unfortunately, they do not regenerate upon injury in mammals. In ON trauma, retinal microglia (RMG) become activated, inducing inflammatory responses and resulting in axon degeneration and RGC loss. Since aldose reductase (AR) is an inflammatory response mediator highly expressed in RMG, we investigated if pharmacological inhibition of AR can attenuate ocular inflammation and thereby promote RGC survival and axon regeneration after ON crush (ONC). In vitro, we discovered that Sorbinil, an AR inhibitor, attenuates BV2 microglia activation and migration in the lipopolysaccharide (LPS) and monocyte chemoattractant protein-1 (MCP-1) treatments. In vivo, Sorbinil suppressed ONC-induced Iba1 + microglia/macrophage infiltration in the retina and ON and promoted RGC survival. Moreover, Sorbinil restored RGC function and delayed axon degeneration one week after ONC. RNA sequencing data revealed that Sorbinil protects the retina from ONC-induced degeneration by suppressing inflammatory signaling. In summary, we report the first study demonstrating that AR inhibition transiently protects RGC and axon from degeneration, providing a potential therapeutic strategy for optic neuropathies.

GLP-1R agonists demonstrate potential to treat Wolfram syndrome in human preclinical models.

AIMS/HYPOTHESIS: Wolfram syndrome is a rare autosomal recessive disorder caused by pathogenic variants in the WFS1 gene. It is characterised by insulin-dependent diabetes mellitus, optic nerve atrophy, diabetes insipidus, hearing loss and neurodegeneration. Considering the unmet treatment need for this orphan disease, this study aimed to evaluate the therapeutic potential of glucagon-like peptide 1 receptor (GLP-1R) agonists under wolframin (WFS1) deficiency with a particular focus on human beta cells and neurons. METHODS: The effect of the GLP-1R agonists dulaglutide and exenatide was examined in Wfs1 knockout mice and in an array of human preclinical models of Wolfram syndrome, including WFS1-deficient human beta cells, human induced pluripotent stem cell (iPSC)-derived beta-like cells and neurons from control individuals and individuals affected by Wolfram syndrome, and humanised mice. RESULTS: Our study shows that the long-lasting GLP-1R agonist dulaglutide reverses impaired glucose tolerance in WFS1-deficient mice, and that exenatide and dulaglutide improve beta cell function and prevent apoptosis in different human WFS1-deficient models including iPSC-derived beta cells from people with Wolfram syndrome. Exenatide improved mitochondrial function, reduced oxidative stress and prevented apoptosis in Wolfram syndrome iPSC-derived neural precursors and cerebellar neurons. CONCLUSIONS/INTERPRETATION: Our study provides novel evidence for the beneficial effect of GLP-1R agonists on WFS1-deficient human pancreatic beta cells and neurons, suggesting that these drugs may be considered as a treatment for individuals with Wolfram syndrome.

Expanding SPG7 dominant optic atrophy phenotype: Infantile nystagmus and optic atrophy without spastic paraplegia.

Spastic paraplegia is a neurodegenerative disorder characterized by progressive leg weakness and spasticity due to degeneration of corticospinal axons. SPG7 encodes paraplegin, and pathogenic variants in the gene cause hereditary spastic paraplegia as an autosomal recessive trait. Various ophthalmological findings including optic atrophy, ophthalmoplegia, or nystagmus have been reported in patients with spastic paraplegia type 7. We report a 15-year-old male patient with a novel heterozygous variant, c.1224T>G:p.(Asp408Glu) in SPG7 (NM_003119.3) causing early onset isolated optic atrophy and infantile nystagmus prior to the onset of neurological symptoms. Therefore, SPG7 should be considered a cause of infantile nystagmus with optic atrophy.

Multidimensional analysis and therapeutic development using patient iPSC-derived disease models of Wolfram syndrome.

Wolfram syndrome is a rare genetic disorder largely caused by pathogenic variants in the WFS1 gene and manifested by diabetes mellitus, optic nerve atrophy, and progressive neurodegeneration. Recent genetic and clinical findings have revealed Wolfram syndrome as a spectrum disorder. Therefore, a genotype-phenotype correlation analysis is needed for diagnosis and therapeutic development. Here, we focus on the WFS1 c.1672C>T, p.R558C variant, which is highly prevalent in the Ashkenazi Jewish population. Clinical investigation indicated that patients carrying the homozygous WFS1 c.1672C>T, p.R558C variant showed mild forms of Wolfram syndrome phenotypes. Expression of WFS1 p.R558C was more stable compared with the other known recessive pathogenic variants associated with Wolfram syndrome. Human induced pluripotent stem cell-derived (iPSC-derived) islets (SC-islets) homozygous for WFS1 c.1672C>T variant recapitulated genotype-related Wolfram syndrome phenotypes. Enhancing residual WFS1 function through a combination treatment of chemical chaperones mitigated detrimental effects caused by the WFS1 c.1672C>T, p.R558C variant and increased insulin secretion in SC-islets. Thus, the WFS1 c.1672C>T, p.R558C variant causes a mild form of Wolfram syndrome phenotypes, which can be remitted with a combination treatment of chemical chaperones. We demonstrate that our patient iPSC-derived disease model provides a valuable platform for further genotype-phenotype analysis and therapeutic development for Wolfram syndrome.

Comprehensive Genetic Analysis Unraveled the Missing Heritability in a Chinese Cohort With Wolfram Syndrome 1: Clinical and Genetic Findings.

Purpose: To identify the missing heritability of patients with Wolfram syndrome 1 (WFS1) in a Chinese cohort and to report their clinical and genetic features. Methods: We recruited 24 unrelated patients with suspected WFS1 who carried at least one variant in WFS1. All patients underwent ophthalmic examinations and comprehensive molecular genetic analyses, including Sanger-DNA sequencing of WFS1 and next-generation sequencing of the whole WFS1 sequence. Results: We identified 38 distinct pathogenic variants of WFS1 in the 24 probands, comprising 23 patients with biallelic variants and one patient with a monoallelic variant. Sanger-DNA sequencing of WFS1 initially detected 35 variants, and subsequent whole genome sequencing revealed three missing variants: one novel deep intronic variant (DIV), one copy number variant (CNV), and one variant in the promoter region. Minigene assays showed that the DIV activated cryptic splice sites, leading to the insertion of pseudoexons. Optic atrophy was observed in all patients, and diabetes mellitus (DM) was revealed in 21 patients (91.3%), hearing loss in nine patients (39.1%), renal tract abnormalities in nine patients (39.1%), and diabetes insipidus in five patients (21.7%). The mean onset age for DM was significantly younger in the patients with biallelic null variants than in the patients with biallelic missense variants. Conclusions: Our results extend the pathogenic variant spectrum of WFS1. DIVs and CNVs explained rare unresolved Chinese cases with WFS1. The patients showed a wide and variable clinical spectrum, supporting the importance of genetic analysis for patients with atypical WFS1.

First Description of Inheritance of a Postzygotic OPA1 Mosaic Variant.

Optic atrophy 1 (MIM #165500) is caused by pathogenic variants in the gene OPA1 (OPA1 MITOCHONDRIAL DYNAMIN-LIKE GTPase, MIM *605290) and is inherited in an autosomal dominant manner. We describe a 6-year-old male patient with severe early onset manifestation of optic atrophy, whose parents are subjectively asymptomatic. OPA1-sequence analysis revealed the heterozygous missense variant NM_015560.3:c.806C>T, p.(Ser269Phe) in the patient. Segregation analysis of the parents showed that the mother carried a low-grade postzygotic mosaic of this variant, which apparently also involves germline cells. In line with this, ophthalmological investigation of the mother showed subclinical manifestation of optic atrophy 1. This is the first report of an OPA1 postzygotic mosaic that was inherited to offspring.

Neuroglobin effectively halts vision loss in Harlequin mice at an advanced stage of optic nerve degeneration.

Mitochondrial diseases are among the most prevalent groups of inherited neurological disorders, affecting up to 1 in 5000 adults. Despite the progress achieved on the identification of gene mutations causing mitochondrial pathologies, they cannot be cured so far. Harlequin mice, a relevant model of mitochondrial pathology due to apoptosis inducing factor depletion, suffer from progressive disappearance of retinal ganglion cells leading to optic neuropathy. In our previous work, we showed that administering adeno-associated virus encompassing the coding sequences for neuroglobin, (a neuroprotective molecule belonging to the globin family) or apoptosis-inducing factor, before neurodegeneration onset, prevented retinal ganglion cell loss and preserved visual function. One of the challenges to develop an effective treatment for optic neuropathies is to consider that by the time patients become aware of their handicap, a large amount of nerve fibers has already disappeared. Gene therapy was performed in Harlequin mice aged between 4 and 5 months with either a neuroglobin or an apoptosis-inducing factor vector to determine whether the increased abundance of either one of these proteins in retinas could preserve visual function at this advanced stage of the disease. We demonstrated that gene therapy, by preserving the connectivity of transduced retinal ganglion cells and optic nerve bioenergetics, results in the enhancement of visual cortex activity, ultimately rescuing visual impairment. This study demonstrates that: (a) An increased abundance of neuroglobin functionally overcomes apoptosis-inducing factor absence in Harlequin mouse retinas at a late stage of neuronal degeneration; (b) The beneficial effect for visual function could be mediated by neuroglobin localization to the mitochondria, thus contributing to the maintenance of the organelle homeostasis.

[A novel frameshift NDUFV1 mutation in a child with the phenotype of optic nerve atrophy].

OBJECTIVE: To investigate the pathogenic gene in a child with optic atrophy and analyze the influence of this gene mutation on protein structure. OBJECTIVE: We collected the clinical record of the 13-year-old girl and her relatives. The child received examinations of the visual acuity, visual field, fundus, OCT, visual-evoked potential (VEP) and the nerve system, underwent brain MRI and was followed up for 1 year. Genomic DNA was extracted from the peripheral blood of the child and her parents for next-generation sequencing of the whole exon. The pathogenic gene mutation was identified and the resultant changes in the protein structure was analyzed. OBJECTIVE: The patient presented with impaired vision and optic nerve atrophy in both eyes with low amplitude of VEP, but did not show dystonia or pyramidal tract symptom. Brain MRI detected no leukodystrophy. Genetic analysis suggested a heterozygous c.53_54delTG mutation in exon 1 in the NDUFV1 gene of complex I, which caused a frameshift starting with the codon valine 18, thus changing the amino acid to an Alanine residue and creating a premature stop codon at position 20 of the new reading frame (p.Val18AlafsX20). A heterozygous for c.1162+4A>C: IVS8 + 4A>C in intron 8 was also found. Protein structure analysis showed the missing of important structure of NDUFV1 subunit in complex I. OBJECTIVE: We identified a novel NDUFV1 mutation in a child with optic nerve atrophy. This finding may provide further insight into the genotype-phenotype correlations for NDUFV1 gene.

Focal dystonia in a case of SYNE1 spastic-ataxia: Expanding the phenotypic spectrum.

Synaptic nuclear envelope protein-1 (SYNE1) related cerebellar ataxia also called ARCA1 or SCAR8, manifests as a relatively pure cerebellar ataxia or with additional neurological involvement. Dystonia is rarely seen in SYNE1 ataxia and to the best of our knowledge, there are only three reports of dystonia in patients with SYNE1 ataxia. This report describes a 22-year-old woman with chronic progressive spastic-ataxia of 3-year duration with additional focal dystonia of the right upper limb. Patient had cerebellar atrophy on MRI brain and a novel pathogenic homozygous variant in exon 74 of the SYNE1 gene (p.Gln4047Ter).

NDUFS3 depletion permits complex I maturation and reveals TMEM126A/OPA7 as an assembly factor binding the ND4-module intermediate.

Complex I (CI) is the largest enzyme of the mitochondrial respiratory chain, and its defects are the main cause of mitochondrial disease. To understand the mechanisms regulating the extremely intricate biogenesis of this fundamental bioenergetic machine, we analyze the structural and functional consequences of the ablation of NDUFS3, a non-catalytic core subunit. We show that, in diverse mammalian cell types, a small amount of functional CI can still be detected in the complete absence of NDUFS3. In addition, we determine the dynamics of CI disassembly when the amount of NDUFS3 is gradually decreased. The process of degradation of the complex occurs in a hierarchical and modular fashion in which the ND4 module remains stable and bound to TMEM126A. We, thus, uncover the function of TMEM126A, the product of a disease gene causing recessive optic atrophy as a factor necessary for the correct assembly and function of CI.

Wolfram-like syndrome with bicuspid aortic valve due to a homozygous missense variant in CDK13.

BACKGROUND: Wolfram syndrome (WFS) is characterized by deafness, diabetes mellitus, and diabetes insipidus along with optic atrophy. WFS has an autosomal recessive mode of inheritance and is due to variants in WFS1 and CISD2. METHODS: We evaluated the underlying molecular etiology of three affected members of a consanguineous family with hearing impairment, bicuspid aortic valve, diabetes mellitus and insipidus, clinodactyly, and gastrointestinal tract abnormalities via exome sequencing approach. We correlated clinical and imaging data with the genetic findings and their associated phenotypes. RESULTS: We identified a homozygous missense variant p.(Asn1097Lys) in CDK13, a gene previously associated with autosomal dominant congenital heart defects, dysmorphic facial features, clinodactyly, gastrointestinal tract abnormalities, intellectual developmental disorder, and seizures with variable phenotypic features. CONCLUSION: We report a homozygous variant in CDK13 and suggest that this gene causes an autosomal recessive disorder with hearing impairment, bicuspid aortic valve, diabetes mellitus and insipidus, clinodactyly, and gastrointestinal tract abnormalities.

Optic Atrophy and Inner Retinal Thinning in CACNA1F-related Congenital Stationary Night Blindness.

Hemizygous pathogenic variants in CACNA1F lead to defective signal transmission from retinal photoreceptors to bipolar cells and cause incomplete congenital stationary night blindness in humans. Although the primary defect is at the terminal end of first-order neurons (photoreceptors), there is limited knowledge of higher-order neuronal changes (inner retinal) in this disorder. This study aimed to investigate inner retinal changes in CACNA1F-retinopathy by analyzing macular ganglion cell layer-inner plexiform layer (GCL-IPL) thickness and optic disc pallor in 22 subjects with molecularly confirmed CACNA1F-retinopathy. Detailed ocular phenotypic data including distance and color vision, refraction and electroretinogram (ERG) were collected. Distance vision was universally reduced (mean: 0.42 LogMAR), six had abnormal color vision and myopia was common (n = 15; mean: -6.32 diopters). Mean GCL-IPL thickness was significantly lower in patients (55.00 µm) compared to age-matched controls (n = 87; 84.57 µm; p << 0.001). The GCL-IPL thickness correlated with scotopic standard (p = 0.04) and bright-flash (p = 0.014) ERG b/a ratios and photopic b-wave amplitudes (p = 0.05). Twenty-one patients had some degree of disc pallor (bilateral in 19). Fifteen putative disease-causing, including five novel variants were identified. This study establishes macular inner retinal thinning and optic atrophy as characteristic features of CACNA1F-retinopathy, which are independent of myopia and could impact potential future treatment strategies.

Homozygous TFG gene variants expanding the mutational and clinical spectrum of hereditary spastic paraplegia 57 and a review of literature.

In recent years, the tropomyosin-receptor kinase fused gene (TFG) has been linked to diverse hereditary neurodegenerative disorders, including a very rare complex hereditary spastic paraplegia, named spastic paraplegia type 57 (SPG57). Until now, four pathogenic homozygous variants of the TFG gene have been reported associated with SPG57. Two consanguineous Iranian families (1 and 2), the first one with two affected members and the second one with one, all with an early-onset progressive muscle weakness, spasticity, and several neurological symptoms were examined via the whole-exome sequencing. Two homozygous missense variants including c.41A>G (p.Lys14Arg) and c.316C>T (p.Arg106Cys) have been found in the related families. The candidate variants were confirmed by Sanger sequencing and found to co-segregate with the disease in families. The bioinformatics analysis showed the deleterious effects of these nucleotide changes and the variants were classified as pathogenic according to ACMG guidelines. A comparison of the clinical presentation of the patients harboring c.41A>G (p.Lys14Arg) with previously reported SPG57 revealed variability in the severity state and unreported clinical presentation, including, facial atrophy, nystagmus, hyperelastic skin, cryptorchidism, hirsutism, kyphoscoliosis, and pectus excavatum. The affected member of the second family carried a previously reported homozygous c.316C>T (p.Arg106Cys) variant and displayed a complex HSP including optic atrophy. Remarkable clinical differences were observed between the family 1 and 2 harboring the c.41A>G (p.Lys14Arg) and c.316C>T (p.Arg106Cys) variants, which could be attributed to the distinct affected domains (PB1 domains and coiled-coil domains), and therefore, SPG57 might have been representing phenotype vs. variant position correlation.

Exome sequencing identifies novel missense and deletion variants in RTN4IP1 associated with optic atrophy, global developmental delay, epilepsy, ataxia, and choreoathetosis.

Inherited optic neuropathies (IONs) are neurodegenerative disorders characterized by optic atrophy with or without extraocular manifestations. Optic atrophy-10 (OPA10) is an autosomal recessive ION recently reported to be caused by mutations in RTN4IP1, which encodes reticulon 4 interacting protein 1 (RTN4IP1), a mitochondrial ubiquinol oxydo-reductase. Here we report novel compound heterozygous mutations in RTN4IP1 in a male proband with developmental delay, epilepsy, optic atrophy, ataxia, and choreoathetosis. Workup was notable for transiently elevated lactate and lactate-to-pyruvate ratio, brain magnetic resonance imaging with optic atrophy and T2 signal abnormalities, and a nondiagnostic initial genetic workup, including chromosomal microarray and mitochondrial panel testing. Exome sequencing identified a paternally inherited missense variant (c.263T>G, p.Val88Gly) predicted to be deleterious and a maternally inherited deletion encompassing RTN4IP1. To our knowledge, this is the first report of a non-single nucleotide pathogenic variant associated with OPA10. This case highlights the expanding phenotypic spectrum of OPA10, the association between "syndromic" cases and severe RTN4IP1 mutations, and the importance of nonbiased genetic testing, such as ES, to analyze multiple genes and variants types, in patients suspected of having genetic disease.

The Warburg Micro Syndrome-associated Rab3GAP-Rab18 module promotes autolysosome maturation through the Vps34 Complex I.

Warburg micro syndrome (WMS) is a hereditary autosomal neuromuscular disorder in humans caused by mutations in Rab18, Rab3GAP1, or Rab3GAP2 genes. Rab3GAP1/2 forms a heterodimeric complex, which acts as a guanosine nucleotide exchange factor and activates Rab18. Although the genetic causes of WMS are known, it is still unclear whether loss of the Rab3GAP-Rab18 module affects neuronal or muscle cell physiology or both, and how. In this work, we characterize a Rab3GAP2 mutant Drosophila line to establish a novel animal model for WMS. Similarly to symptoms of WMS, loss of Rab3GAP2 leads to highly decreased motility in Drosophila that becomes more serious with age. We demonstrate that these mutant flies are defective for autophagic degradation in multiple tissues including fat cells and muscles. Loss of Rab3GAP-Rab18 module members leads to perturbed autolysosome morphology due to destabilization of Rab7-positive autophagosomal and late endosomal compartments and perturbation of lysosomal biosynthetic transport. Importantly, overexpression of UVRAG or loss of Atg14, two alternative subunits of the Vps34/PI3K (vacuole protein sorting 34/phosphatidylinositol 3-kinase) complexes in fat cells, mimics the autophagic phenotype of Rab3GAP-Rab18 module loss. We find that GTP-bound Rab18 binds to Atg6/Beclin1, a permanent subunit of Vps34 complexes. Finally, we show that Rab3GAP2 and Rab18 are present on autophagosomal and autolysosomal membranes and colocalize with Vps34 Complex I subunits. Our data suggest that the Rab3GAP-Rab18 module regulates autolysosomal maturation through its interaction with the Vps34 Complex I, and perturbed autophagy due to loss of the Rab3GAP-Rab18 module may contribute to the development of WMS.