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Activity-dependent specification of neuronal architecture during early postnatal life is essential for refining the precision of communication between neurons. In the spinal cord under normal circumstances, the AMPA receptor subunit GluR1 is expressed at high levels by motor neurons and surrounding interneurons during this critical developmental period, although the role it plays in circuit formation and locomotor behavior is unknown. Here, we show that GluR1 promotes dendrite growth in a non-cell-autonomous manner in vitro and in vivo. The mal-development of motor neuron dendrites is associated with changes in the pattern of interneuronal connectivity within the segmental spinal cord and defects in strength and endurance. Transgenic expression of GluR1 in adult motor neurons leads to dendrite remodeling and supernormal locomotor function. GluR1 expression by neurons within the segmental spinal cord plays an essential role in formation of the neural network that underlies normal motor behavior. [ABSTRACT FROM AUTHOR]

During the past decade, outstanding progress in the areas of congenital and limb-girdle muscular dystrophies has led to staggering clinical and genetic complexity. With the identification of an increasing number of genetic defects, individual entities have come into sharper focus and new pathogenic mechanisms for muscular dystrophies, like defects of posttranslational O-linked glycosylation, have been discovered. At the same time, this progress blurs the traditional boundaries between the categories of congenital and limb-girdle muscular dystrophies, as well as between limb-girdle muscular dystrophies and other clinical entities, as mutations in genes such as fukutin-related protein, dysferlin, caveolin-3 and lamin A/C can cause a striking variety of phenotypes. We reviewed the different groups of proteins currently recognized as being involved in congenital and limb-girdle muscular dystrophies, associated them with the clinical phenotypes, and determined some clinical and molecular clues that are helpful in the diagnostic approach to these patients. [ABSTRACT FROM AUTHOR]

Examines the function and organization of sarcoglycan complex in cultured mouse myotubes. Localization of sarcoglycans to membrane function of differentiated mouse myotubes; Association between beta- and delta-sarcoglycan; Crosslinking of sarcoglycans in vivo.

Collagen VI-related muscular dystrophies (COL6-RD) comprise a continuous spectrum of clinical severity, ranging from the most severe phenotype Ullrich congenital muscular dystrophy (UCMD), through intermediate phenotypes, to a milder Bethlem myopathy (BM) (1). These inherited diseases are caused by autosomal dominant or recessive mutations in the genes COL6A1, COL6A2 and COL6A3, which encode the main 3 α-chains of collagen VI, a component of the extracellular matrix (ECM) that is present in the vast majority of connective tissues and is implicated in its organization (2). The prevalence of COL6-RD is estimated as 0.77:100,000 in BM and 0.13:100,000 in UCMD (3). Clinical features are secondary to the dysfunction of the collagen VI in the ECM of muscle and connective tissues of tendons, subcutaneous and dermal layers of the skin (1, 2). BM is characterized by slow progressive weakness of the proximal muscles and contractures that characteristically involve multiple joints. Although the course of the disease is slowly progressive, many patients exhibit a marked decrease in muscle strength between the 4th and 5th decades, with approximately half of them becoming wheelchair-dependant after the 5th decade (1, 2). Cutaneous manifestations include: presence of keratosis pilaris, mostly in the extensor surfaces of proximal legs and arms; formation of abnormal scars, especially keloids, either spontaneous or after minor trauma; rough or dry skin; striae rubrae; cigarette paper scars; and, in younger patients with UCMD, soft velvety skin on the palms and soles (4-7). Preclinical studies have observed decreased tensile strength of the skin and altered collagen fibril and basement membrane architecture in Col6a1 null mice (8). We report here a case of spontaneous formation of keloids in a previously non-diagnosed BM patient who had 3 daughters also displaying features of BM. [ABSTRACT FROM AUTHOR]

Analyzes muscle biopsies from a Duchenne muscular dystrophy (DMD) patient who received bone marrow transplantation for X-linked severe combined immune deficiency. Analysis of skin, marrow and peripheral blood DNA samples; Clinical history of the patient; Molecular diagnosis of DMD-BMT1.

Background: Neurogenetic disorders caused by pathogenic variants in four genes encoding non-erythrocytic spectrins ( SPTAN1, SPTBN1, SPTBN2, SPTBN4) range from peripheral and central nervous system involvement to complex syndromic presentations. Heterozygous pathogenic variants in SPTAN1 are exemplary for this diversity with phenotypes spanning almost the entire spectrum., Methods: Through international collaboration we identified 14 families with genetically unsolved distal weakness and unreported heterozygous SPTAN1 loss-of-function variants including frameshift, nonsense and splice-acceptor variants. Clinical data, electrophysiology, muscle CT or MRI and muscle biopsy findings were collected and standardized. SPTAN1 protein, mRNA expression analysis and cDNA sequencing was performed on muscle tissue from two patients., Results: All 20 patients presented with early childhood onset distal weakness. The severity varied both within families and between different families. Foot abnormalities ranged from hammer toes and pes cavus to distal arthrogryposis. Electrophysiology showed mixed myogenic and neurogenic features. Muscle MRI or CT in 10 patients showed fatty infiltration of the distal lower limb anterior compartment and/or selective involvement of the extensor hallucis longus muscle. Muscle biopsy revealed myopathic changes with mild dystrophic and chronic neurogenic changes in 7 patients. Finally, we provide proof for nonsense mediated decay in tissues derived from two patients., Conclusions: We provide evidence for the association of SPTAN1 loss-of-function variants with childhood onset distal myopathy in 14 families. This finding extends the phenotypic spectrum of SPTAN1 loss-of-function variants ranging from intellectual disability to distal weakness with a predominant myogenic cause., Key Messages: SPTAN1 loss-of-function variants, including frameshift, nonsense and splice site variants cause a novel childhood onset distal weakness syndrome with primarily skeletal muscle involvement. Hereditary motor neuropathies and distal myopathic disorders present a well-known diagnostic challenge as they demonstrate substantial clinical and genetic overlap. The emergence of SPTAN1 loss-of-function variants serves as a noteworthy example, highlighting a growing convergence in the spectrum of genotypes linked to both hereditary motor neuropathies and distal myopathies.

There are more than 10,000 individual rare diseases and most are without therapy. Personalized genetic therapy represents one promising approach for their treatment. We present a road map for individualized treatment of an ultra-rare disease by establishing a gene replacement therapy developed for a single patient with hereditary spastic paraplegia type 50 (SPG50). Through a multicenter collaboration, an adeno-associated virus-based gene therapy product carrying the AP4M1 gene was created and successfully administered intrathecally to a 4-year-old patient within 3 years of diagnosis as part of a single-patient phase 1 trial. Primary endpoints were safety and tolerability, and secondary endpoints evaluated efficacy. At 12 months after dosing, the therapy was well tolerated. No serious adverse events were observed, with minor events, including transient neutropenia and Clostridioides difficile gastroenteritis, experienced but resolved. Preliminary efficacy measures suggest a stabilization of the disease course. Longer follow-up is needed to confirm the safety and provide additional insights on the efficacy of the therapy. Overall, this report supports the safety of gene therapy for SPG50 and provides insights into precision therapy development for rare diseases. Clinical trial registration: NCT06069687 ., (© 2024. The Author(s).)

A host of medical conditions, including amputations, diabetes, stroke, and genetic disease, result in loss of touch sensation. Because most types of sensory loss have no pharmacological treatment or rehabilitative therapy, we propose a haptic sensory prosthesis that provides substitutive feedback. The wrist and forearm are compelling locations for feedback due to available skin area and not occluding the hands, but have reduced mechanoreceptor density compared to the fingertips. Focusing on localized pressure as the feedback modality, we hypothesize that we can improve on prior devices by invoking a wider range of stimulus intensity using multiple points of pressure to evoke spatial summation, which is the cumulative perceptual experience from multiple points of stimuli. We conducted a preliminary perceptual test to investigate this idea and found that just noticeable difference is reduced with two points of pressure compared to one, motivating future work using spatial summation in sensory prostheses.

Giant Axonal Neuropathy (GAN) is a pediatric neurodegenerative disease caused by KLHL16 mutations. KLHL16 encodes gigaxonin, which regulates intermediate filament (IF) turnover. Previous neuropathological studies and examination of postmortem brain tissue in the current study revealed involvement of astrocytes in GAN. To develop a clinically-relevant model, we reprogrammed skin fibroblasts from seven GAN patients to pluripotent stem cells (iPSCs), which were used to generate neural progenitor cells (NPCs), astrocytes, and brain organoids. Multiple isogenic control clones were derived via CRISPR/Cas9 gene editing of one patient line carrying the G332R gigaxonin mutation. All GAN iPSCs were deficient for gigaxonin and displayed patient-specific increased vimentin expression. GAN NPCs had lower nestin expression and fewer nestin-positive cells compared to isogenic controls, but nestin morphology was unaffected. GAN brain organoids were marked by the presence of neurofilament and GFAP aggregates. GAN iPSC-astrocytes displayed striking dense perinuclear vimentin and GFAP accumulations and abnormal nuclear morphology. In over-expression systems, GFAP oligomerization and perinuclear aggregation were augmented in the presence of vimentin. GAN patient cells with large perinuclear vimentin aggregates accumulated significantly more nuclear KLHL16 mRNA compared to cells without vimentin aggregates. As an early effector of KLHL16 mutations, vimentin may be a potential target in GAN.

X-linked myotubular myopathy (XLMTM) is a fatal neuromuscular disorder caused by loss of function mutations in MTM1. At present, there are no directed therapies for XLMTM, and incomplete understanding of disease pathomechanisms. To address these knowledge gaps, we performed a drug screen in mtm1 mutant zebrafish and identified four positive hits, including valproic acid, which functions as a potent suppressor of the mtm1 zebrafish phenotype via HDAC inhibition. We translated these findings to a mouse XLMTM model, and showed that valproic acid ameliorates the murine phenotype. These observations led us to interrogate the epigenome in Mtm1 knockout mice; we found increased DNA methylation, which is normalized with valproic acid, and likely mediated through aberrant 1-carbon metabolism. Finally, we made the unexpected observation that XLMTM patients share a distinct DNA methylation signature, suggesting that epigenetic alteration is a conserved disease feature amenable to therapeutic intervention., (© 2022. The Author(s).)

Background and Objectives: Facioscapulohumeral muscular dystrophy type 2 (FSHD2) and arhinia are 2 distinct disorders caused by pathogenic variants in the same gene: SMCHD1 . The mechanism underlying this phenotypic divergence remains unclear. In this study, we characterize the neuromuscular phenotype of individuals with arhinia caused by SMCHD1 variants and analyze their complex genetic and epigenetic criteria to assess their risk for FSHD2., Methods: Eleven individuals with congenital nasal anomalies, including arhinia, nasal hypoplasia, or anosmia, underwent a neuromuscular examination, genetic testing, muscle ultrasound, and muscle MRI. Risk for FSHD2 was determined by combined genetic and epigenetic analysis of 4q35 haplotype, D4Z4 repeat length, and methylation profile. We also compared expression levels of pathogenic DUX4 mRNA in primary myoblasts or dermal fibroblasts (upon myogenic differentiation or epigenetic transdifferentiation, respectively) in these individuals vs those with confirmed FSHD2., Results: Among the 11 individuals with rare, pathogenic, heterozygous missense variants in exons 3-11 of SMCHD1, only a subset (n = 3/11; 1 male, 2 female; age 25-51 years) met the strict genetic and epigenetic criteria for FSHD2 (D4Z4 repeat unit length <21 in cis with a 4qA haplotype and D4Z4 methylation <30%). None of the 3 individuals had typical clinical manifestations or muscle imaging findings consistent with FSHD2. However, the patients with arhinia meeting the permissive genetic and epigenetic criteria for FSHD2 displayed some DUX4 expression in dermal fibroblasts under the epigenetic de-repression by drug treatment and in the primary myoblasts undergoing myogenic differentiation., Discussion: In this cross-sectional study, we identified patients with arhinia who meet the full genetic and epigenetic criteria for FSHD2 and display the molecular hallmark of FSHD- DUX4 de-repression and expression in vitro-but who do not manifest with the typical clinicopathologic phenotype of FSHD2. The distinct dichotomy between FSHD2 and arhinia phenotypes despite an otherwise poised DUX4 locus implies the presence of novel disease-modifying factors that seem to operate as a switch, resulting in one phenotype and not the other. Identification and further understanding of these disease-modifying factors will provide valuable insight with therapeutic implications for both diseases., (Written work prepared by employees of the Federal Government as part of their official duties is, under the U.S. Copyright Act, a “work of the United States Government” for which copyright protection under Title 17 of the United States Code is not available. As such, copyright does not extend to the contributions of employees of the Federal Government.)

Transcriptome data can facilitate the interpretation of the effects of rare genetic variants. Here, we introduce ANEVA (analysis of expression variation) to quantify genetic variation in gene dosage from allelic expression (AE) data in a population. Application of ANEVA to the Genotype-Tissues Expression (GTEx) data showed that this variance estimate is robust and correlated with selective constraint in a gene. Using these variance estimates in a dosage outlier test (ANEVA-DOT) applied to AE data from 70 Mendelian muscular disease patients showed accuracy in detecting genes with pathogenic variants in previously resolved cases and led to one confirmed and several potential new diagnoses. Using our reference estimates from GTEx data, ANEVA-DOT can be incorporated in rare disease diagnostic pipelines to use RNA-sequencing data more effectively., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

Congenital muscular dystrophies are a group of rare neuromuscular disorders with a wide spectrum of clinical phenotypes. Recent advances in understanding the molecular pathogenesis of congenital muscular dystrophy have enabled better diagnosis. However, medical care for patients with congenital muscular dystrophy remains very diverse. Advances in many areas of medical technology have not been adopted in clinical practice. The International Standard of Care Committee for Congenital Muscular Dystrophy was established to identify current care issues, review literature for evidence-based practice, and achieve consensus on care recommendations in 7 areas: diagnosis, neurology, pulmonology, orthopedics/rehabilitation, gastroenterology/ nutrition/speech/oral care, cardiology, and palliative care. To achieve consensus on the care recommendations, 2 separate online surveys were conducted to poll opinions from experts in the field and from congenital muscular dystrophy families. The final consensus was achieved in a 3-day workshop conducted in Brussels, Belgium, in November 2009. This consensus statement describes the care recommendations from this committee., Competing Interests: Declaration of Conflicting Interests The authors declared no potential conflicts of interest with respect to the authorship and/or publication of this article.

Activity-dependent specification of neuronal architecture during early postnatal life is essential for refining the precision of communication between neurons. In the spinal cord under normal circumstances, the AMPA receptor subunit GluR1 is expressed at high levels by motor neurons and surrounding interneurons during this critical developmental period, although the role it plays in circuit formation and locomotor behavior is unknown. Here, we show that GluR1 promotes dendrite growth in a non-cell-autonomous manner in vitro and in vivo. The mal-development of motor neuron dendrites is associated with changes in the pattern of interneuronal connectivity within the segmental spinal cord and defects in strength and endurance. Transgenic expression of GluR1 in adult motor neurons leads to dendrite remodeling and supernormal locomotor function. GluR1 expression by neurons within the segmental spinal cord plays an essential role in formation of the neural network that underlies normal motor behavior.