Heterozygous MAP3K20 variants cause ectodermal dysplasia, craniosynostosis, sensorineural hearing loss, and limb anomalies.

Biallelic pathogenic variants in MAP3K20, which encodes a mitogen-activated protein kinase, are a rare cause of split-hand foot malformation (SHFM), hearing loss, and nail abnormalities or congenital myopathy. However, heterozygous variants in this gene have not been definitively associated with a phenotype. Here, we describe the phenotypic spectrum associated with heterozygous de novo variants in the linker region between the kinase domain and leucine zipper domain of MAP3K20. We report five individuals with diverse clinical features, including craniosynostosis, limb anomalies, sensorineural hearing loss, and ectodermal dysplasia-like phenotypes who have heterozygous de novo variants in this specific region of the gene. These individuals exhibit both shared and unique clinical manifestations, highlighting the complexity and variability of the disorder. We propose that the involvement of MAP3K20 in endothelial-mesenchymal transition provides a plausible etiology of these features. Together, these findings characterize a disorder that both expands the phenotypic spectrum associated with MAP3K20 and highlights the need for further studies on its role in early human development.

Inheritance of c.628-6G>A GNB5 hypomorphic allele uncovers another challenge in the pathogenic prediction of genomic variants.

We studied a patient with a severe phenotype carrying two GNB5 variants: c.514delT from the unaffected heterozygous mother and c.628-6G>A from the unaffected homozygous father. Functional genomics studies showed that parents express 50% (nonsense-mediated decay, NMD) of the RNA/protein while the patient does not produce enough protein for normal development.

Mitochondria-lysosome membrane contacts are defective in GDAP1-related Charcot-Marie-Tooth disease.

Mutations in the GDAP1 gene cause Charcot-Marie-Tooth (CMT) neuropathy. GDAP1 is an atypical glutathione S-transferase (GST) of the outer mitochondrial membrane and the mitochondrial membrane contacts with the endoplasmic reticulum (MAMs). Here, we investigate the role of this GST in the autophagic flux and the membrane contact sites (MCSs) between mitochondria and lysosomes in the cellular pathophysiology of GDAP1 deficiency. We demonstrate that GDAP1 participates in basal autophagy and that its depletion affects LC3 and PI3P biology in autophagosome biogenesis and membrane trafficking from MAMs. GDAP1 also contributes to the maturation of lysosome by interacting with PYKfyve kinase, a pH-dependent master lysosomal regulator. GDAP1 deficiency causes giant lysosomes with hydrolytic activity, a delay in the autophagic lysosome reformation, and TFEB activation. Notably, we found that GDAP1 interacts with LAMP-1, which supports that GDAP1-LAMP-1 is a new tethering pair of mitochondria and lysosome membrane contacts. We observed mitochondria-lysosome MCSs in soma and axons of cultured mouse embryonic motor neurons and human neuroblastoma cells. GDAP1 deficiency reduces the MCSs between these organelles, causes mitochondrial network abnormalities, and decreases levels of cellular glutathione (GSH). The supply of GSH-MEE suffices to rescue the lysosome membranes and the defects of the mitochondrial network, but not the interorganelle MCSs nor early autophagic events. Overall, we show that GDAP1 enables the proper function of mitochondrial MCSs in both degradative and nondegradative pathways, which could explain primary insults in GDAP1-related CMT pathophysiology, and highlights new redox-sensitive targets in axonopathies where mitochondria and lysosomes are involved.

Effective therapeutic strategies in a preclinical mouse model of Charcot-Marie-Tooth disease.

Charcot-Marie-Tooth (CMT) disease is a neuropathy that lacks effective therapy. CMT patients show degeneration of peripheral nerves, leading to muscle weakness and loss of proprioception. Loss of mitochondrial oxidative phosphorylation proteins and enzymes of the antioxidant response accompany degeneration of nerves in skin biopsies of CMT patients. Herein, we followed a drug-repurposing approach to find drugs in a Food and Drug Administration-approved library that could prevent development of CMT disease in the Gdap1-null mouse model. We found that the antibiotic florfenicol is a mitochondrial uncoupler that prevents the production of reactive oxygen species and activates respiration in human GDAP1-knockdown neuroblastoma cells and in dorsal root ganglion neurons of Gdap1-null mice. Treatment of CMT-affected Gdap1-null mice with florfenicol has no beneficial effect in the course of the disease. However, administration of florfenicol, or the antioxidant MitoQ, to pre-symptomatic GDAP1-null mice prevented weight gain and ameliorated the motor coordination deficiencies that developed in the Gdap1-null mice. Interestingly, both florfenicol and MitoQ halted the decay in mitochondrial and redox proteins in sciatic nerves of Gdap1-null mice, supporting that oxidative damage is implicated in the etiology of the neuropathy. These findings support the development of clinical trials for translation of these drugs for treatment of CMT patients.

Variants in DTNA cause a mild, dominantly inherited muscular dystrophy.

DTNA encodes α-dystrobrevin, a component of the macromolecular dystrophin-glycoprotein complex (DGC) that binds to dystrophin/utrophin and α-syntrophin. Mice lacking α-dystrobrevin have a muscular dystrophy phenotype, but variants in DTNA have not previously been associated with human skeletal muscle disease. We present 12 individuals from four unrelated families with two different monoallelic DTNA variants affecting the coiled-coil domain of α-dystrobrevin. The five affected individuals from family A harbor a c.1585G > A; p.Glu529Lys variant, while the recurrent c.1567_1587del; p.Gln523_Glu529del DTNA variant was identified in the other three families (family B: four affected individuals, family C: one affected individual, and family D: two affected individuals). Myalgia and exercise intolerance, with variable ages of onset, were reported in 10 of 12 affected individuals. Proximal lower limb weakness with onset in the first decade of life was noted in three individuals. Persistent elevations of serum creatine kinase (CK) levels were detected in 11 of 12 affected individuals, 1 of whom had an episode of rhabdomyolysis at 20 years of age. Autism spectrum disorder or learning disabilities were reported in four individuals with the c.1567_1587 deletion. Muscle biopsies in eight affected individuals showed mixed myopathic and dystrophic findings, characterized by fiber size variability, internalized nuclei, and slightly increased extracellular connective tissue and inflammation. Immunofluorescence analysis of biopsies from five affected individuals showed reduced α-dystrobrevin immunoreactivity and variably reduced immunoreactivity of other DGC proteins: dystrophin, α, ß, δ and γ-sarcoglycans, and α and ß-dystroglycans. The DTNA deletion disrupted an interaction between α-dystrobrevin and syntrophin. Specific variants in the coiled-coil domain of DTNA cause skeletal muscle disease with variable penetrance. Affected individuals show a spectrum of clinical manifestations, with severity ranging from hyperCKemia, myalgias, and exercise intolerance to childhood-onset proximal muscle weakness. Our findings expand the molecular etiologies of both muscular dystrophy and paucisymptomatic hyperCKemia, to now include monoallelic DTNA variants as a novel cause of skeletal muscle disease in humans.

CIBERER: Spanish national network for research on rare diseases: A highly productive collaborative initiative.

CIBER (Center for Biomedical Network Research; Centro de Investigación Biomédica En Red) is a public national consortium created in 2006 under the umbrella of the Spanish National Institute of Health Carlos III (ISCIII). This innovative research structure comprises 11 different specific areas dedicated to the main public health priorities in the National Health System. CIBERER, the thematic area of CIBER focused on rare diseases (RDs) currently consists of 75 research groups belonging to universities, research centers, and hospitals of the entire country. CIBERER's mission is to be a center prioritizing and favoring collaboration and cooperation between biomedical and clinical research groups, with special emphasis on the aspects of genetic, molecular, biochemical, and cellular research of RDs. This research is the basis for providing new tools for the diagnosis and therapy of low-prevalence diseases, in line with the International Rare Diseases Research Consortium (IRDiRC) objectives, thus favoring translational research between the scientific environment of the laboratory and the clinical setting of health centers. In this article, we intend to review CIBERER's 15-year journey and summarize the main results obtained in terms of internationalization, scientific production, contributions toward the discovery of new therapies and novel genes associated to diseases, cooperation with patients' associations and many other topics related to RD research.

Heterozygous variants in ZBTB7A cause a neurodevelopmental disorder associated with symptomatic overgrowth of pharyngeal lymphoid tissue, macrocephaly, and elevated fetal hemoglobin.

By clinical whole exome sequencing, we identified 12 individuals with ages 3 to 37 years, including three individuals from the same family, with a consistent phenotype of intellectual disability (ID), macrocephaly, and overgrowth of adenoid tissue. All 12 individuals harbored a rare heterozygous variant in ZBTB7A which encodes the transcription factor Zinc finger and BTB-domain containing protein 7A, known to play a role in lympho- and hematopoiesis. ID was generally mild. Fetal hemoglobin (HbF) fraction was elevated 2.2%-11.2% (reference value <2% in individuals > 6 months) in four of the five individuals for whom results were available. Ten of twelve individuals had undergone surgery at least once for lymphoid hypertrophy limited to the pharynx. In the most severely affected individual (individual 1), airway obstruction resulted in 17 surgical procedures before the age of 13 years. Sleep apnea was present in 8 of 10 individuals. In the nine unrelated individuals, ZBTB7A variants were novel and de novo. The six frameshift/nonsense and four missense variants were spread throughout the gene. This is the first report of a cohort of individuals with this novel syndromic neurodevelopmental disorder.

Molecular Modelling Hurdle in the Next-Generation Sequencing Era.

There are challenges in the genetic diagnosis of rare diseases, and pursuing an optimal strategy to identify the cause of the disease is one of the main objectives of any clinical genomics unit. A range of techniques are currently used to characterize the genomic variability within the human genome to detect causative variants of specific disorders. With the introduction of next-generation sequencing (NGS) in the clinical setting, geneticists can study single-nucleotide variants (SNVs) throughout the entire exome/genome. In turn, the number of variants to be evaluated per patient has increased significantly, and more information has to be processed and analyzed to determine a proper diagnosis. Roughly 50% of patients with a Mendelian genetic disorder are diagnosed using NGS, but a fair number of patients still suffer a diagnostic odyssey. Due to the inherent diversity of the human population, as more exomes or genomes are sequenced, variants of uncertain significance (VUSs) will increase exponentially. Thus, assigning relevance to a VUS (non-synonymous as well as synonymous) in an undiagnosed patient becomes crucial to assess the proper diagnosis. Multiple algorithms have been used to predict how a specific mutation might affect the protein's function, but they are far from accurate enough to be conclusive. In this work, we highlight the difficulties of genomic variability determined by NGS that have arisen in diagnosing rare genetic diseases, and how molecular modelling has to be a key component to elucidate the relevance of a specific mutation in the protein's loss of function or malfunction. We suggest that the creation of a multi-omics data model should improve the classification of pathogenicity for a significant amount of the detected genomic variability. Moreover, we argue how it should be incorporated systematically in the process of variant evaluation to be useful in the clinical setting and the diagnostic pipeline.

Mitochondria and calcium defects correlate with axonal dysfunction in GDAP1-related Charcot-Marie-Tooth mouse model.

Ganglioside-induced differentiation associated protein 1 (GDAP1) gene encodes a protein of the mitochondrial outer membrane and of the mitochondrial membrane contacts with the endoplasmic reticulum (MAMs) and lysosomes. Since mutations in GDAP1 cause Charcot-Marie-Tooth, an inherited motor and sensory neuropathy, its function is essential for peripheral nerve physiology. Our previous studies showed structural and functional defects in mitochondria and their contacts when GDAP1 is depleted. Nevertheless, the underlying axonal pathophysiological events remain unclear. Here, we have used embryonic motor neurons (eMNs) cultures from Gdap1 knockout (Gdap1-/-) mice to investigate in vivo mitochondria and calcium homeostasis in the axons. We imaged mitochondrial axonal transport and we found a defective pattern in the Gdap1-/- eMNs. We also detected pathological and functional mitochondria membrane abnormalities with a drop in ATP production and a deteriorated bioenergetic status. Another consequence of the loss of GDAP1 in the soma and axons of eMNs was the in vivo increase calcium levels in both basal conditions and during recovery after neuronal stimulation with glutamate. Further, we found that glutamate-stimulation of respiration was lower in Gdap1-/- eMNs showing that the basal bioenergetics failure jeopardizes a full respiratory response and prevents a rapid return of calcium to basal levels. Together, our results demonstrate that the loss of GDAP1 critically compromises the morphology and function of mitochondria and its relationship with calcium homeostasis in the soma and axons, offering important insight into the cellular mechanisms associated with axonal degeneration of GDAP1-related CMT neuropathies and the relevance that axon length may have.

Ethical questions concerning newborn genetic screening.

Newborn screening is a public health strategy used to identify certain diseases in the first days of life and, therefore, facilitate early treatment before the onset of symptoms. The decision of which diseases should be included in a screening goes beyond the medical perspective, including reasons for public health and health economics. There are a number of characteristics to include a disease in the screening, such as that the disorder must be a significant health problem, the natural history of the disease must be well known, a feasible and accurate test must be available, there must be a treatment that is most effective when applied before the onset of clinical symptoms and a health system must be in place that is capable of performing the procedure and subsequent monitoring. Currently, newborn screening programs are currently based on the use of biochemical markers that detect metabolites, hormones or proteins, but recently, the availability of new technology has allowed the possibility of a genetic screening. In addition to technical problems, the possibility of neonatal screening also presents a number of ethical problems. We identified and discussed six areas of particular concern: type of illness, overdiagnosis or overtreatment, information management and informed consent, data confidentiality and protection, justice and legal regulation.

The Increasing Impact of Translational Research in the Molecular Diagnostics of Neuromuscular Diseases.

The diagnosis of neuromuscular diseases (NMDs) has been progressively evolving from the grouping of clinical symptoms and signs towards the molecular definition. Optimal clinical, biochemical, electrophysiological, electrophysiological, and histopathological characterization is very helpful to achieve molecular diagnosis, which is essential for establishing prognosis, treatment and genetic counselling. Currently, the genetic approach includes both the gene-targeted analysis in specific clinically recognizable diseases, as well as genomic analysis based on next-generation sequencing, analyzing either the clinical exome/genome or the whole exome or genome. However, as of today, there are still many patients in whom the causative genetic variant cannot be definitely established and variants of uncertain significance are often found. In this review, we address these drawbacks by incorporating two additional biological omics approaches into the molecular diagnostic process of NMDs. First, functional genomics by introducing experimental cell and molecular biology to analyze and validate the variant for its biological effect in an in-house translational diagnostic program, and second, incorporating a multi-omics approach including RNA-seq, metabolomics, and proteomics in the molecular diagnosis of neuromuscular disease. Both translational diagnostics programs and omics are being implemented as part of the diagnostic process in academic centers and referral hospitals and, therefore, an increase in the proportion of neuromuscular patients with a molecular diagnosis is expected. This improvement in the process and diagnostic performance of patients will allow solving aspects of their health problems in a precise way and will allow them and their families to take a step forward in their lives.

Okur-Chung neurodevelopmental syndrome in a patient from Spain.

Okur-Chung neurodevelopmental syndrome (OCNS, MIM#617062) is a rare autosomal dominant syndrome related to CSNK2A1 mutations. It is characterized by intellectual disability, hypotonia, feeding and speech difficulties, dysmorphic features, and multisystem involvement. To date, less than 30 patients with OCNS have been described in detail in the literature, primarily in Asian populations. Here, we report a 5-year-old Spanish female with OCNS arising from a novel CSNK2A1 mutation c.149A>G, p.Tyr50Cys. Although her clinical features were compatible with OCNS syndrome, magnetic resonance imaging unexpectedly showed a duplication of the pituitary gland, a clinical finding not previously related to any known genetic condition. Other novel signs were an absence of the olfactory bulbs and multiple duplications of cervical vertebrae. We suggest that the midline abnormalities may be a significant part of this condition and lead to diagnostic suspicion. However, further descriptions are needed.

Epilepsy in LAMA2-related muscular dystrophy: An electro-clinico-radiological characterization.

OBJECTIVE: To delineate the epileptic phenotype of LAMA2-related muscular dystrophy (MD) and correlate it with the neuroradiological and muscle biopsy findings, as well as the functional motor phenotype. METHODS: Clinical, electrophysiological, neuroradiological, and histopathological data of 25 patients with diagnosis of LAMA2-related MD were analyzed. RESULTS: Epilepsy occurred in 36% of patients with LAMA2-related MD. Mean age at first seizure was 8 years. The most common presenting seizure type was focal-onset seizures with or without impaired awareness. Visual aura and autonomic signs, including vomiting, were frequently reported. Despite a certain degree of variability, bilateral occipital or temporo-occipital epileptiform abnormalities were by far the most commonly observed. Refractory epilepsy was found in 75% of these patients. Epilepsy in LAMA2-related MD was significantly more prevalent in those patients in whom the cortical malformations were more extensive. In contrast, the occurrence of epilepsy was not found to be associated with the patients' motor ability, the size of their white matter abnormalities, or the amount of residual merosin expressed on muscle. SIGNIFICANCE: The epileptic phenotype of LAMA2-related MD is characterized by focal seizures with prominent visual and autonomic features associated with EEG abnormalities that predominate in the posterior quadrants. A consistent correlation between epileptic phenotype and neuroimaging was identified, suggesting that the extension of the polymicrogyria may serve as a predictor of epilepsy occurrence.

Loss of CLTRN function produces a neuropsychiatric disorder and a biochemical phenotype that mimics Hartnup disease.

Hartnup disease is an autosomal recessive condition characterized by neutral aminoaciduria and behavioral problems. It is caused by a loss of B0 AT1, a neutral amino acid transporter in the kidney and intestine. CLTRN encodes the protein collectrin that functions in the transportation and activation of B0 AT1 in the renal apical brush bordered epithelium. Collectrin deficient mice have severe aminoaciduria. However, the phenotype associated with collectrin deficiency in humans has not been reported. Here we report two patients, an 11-year-old male who is hemizygous for a small, interstitial deletion on Xp22.2 that encompasses CLTRN and a 22-year-old male with a deletion spanning exons 1 to 3 of CLTRN. Both of them present with neuropsychiatric phenotypes including autistic features, anxiety, depression, compulsions, and motor tics, as well as neutral aminoaciduria leading to a clinical diagnosis of Hartnup disease and treatment with niacin supplementation. Plasma amino acids were normal in both patients. One patient had low 5-hydroxyindoleacetic acid levels, a serotoninergic metabolite. We explored the expression of collectrin in the murine brain and found it to be particularly abundant in the hippocampus, brainstem, and cerebellum. We propose that collectrin deficiency in humans can be associated with aminoaciduria and a clinical picture similar to that seen in Hartnup disease. Further studies are needed to explore the role of collectrin deficiency in the neurological phenotypes.

CHRNG-related nonlethal multiple pterygium syndrome: Muscle imaging pattern and clinical, histopathological, and molecular genetic findings.

Mutations in the CHRNG gene cause autosomal recessive multiple pterygium syndrome (MPS). Herein we present a long-term follow-up of seven patients with CHRNG-related nonlethal MPS and we compare them with the 57 previously published patients. The objective is defining not only the clinical, histopathological, and molecular genetic characteristics, but also the type and degree of muscle involvement on whole-body magnetic resonance imaging (WBMRI). CHRNG mutations lead to a distinctive phenotype characterized by multiple congenital contractures, pterygium, and facial dysmorphism, with a stable clinical course over the years. Postnatal abnormalities at the neuromuscular junction were observed in the muscle biopsy of these patients. WBMRI showed distinctive features different from other arthrogryposis multiple congenita. A marked muscle bulk reduction is the predominant finding, mostly affecting the spinal erector muscles and gluteus maximus. Fatty infiltration was only observed in deep paravertebral muscles and distal lower limbs. Mutations in CHRNG are mainly located at the extracellular domain of the protein. Our study contributes to further define the phenotypic spectrum of CHRNG-related nonlethal MPS, including muscle imaging features, which may be useful in distinguishing it from other diffuse arthrogryposis entities.

Calcium Deregulation and Mitochondrial Bioenergetics in GDAP1-Related CMT Disease.

The pathology of Charcot-Marie-Tooth (CMT), a disease arising from mutations in different genes, has been associated with an impairment of mitochondrial dynamics and axonal biology of mitochondria. Mutations in ganglioside-induced differentiation-associated protein 1 (GDAP1) cause several forms of CMT neuropathy, but the pathogenic mechanisms involved remain unclear. GDAP1 is an outer mitochondrial membrane protein highly expressed in neurons. It has been proposed to play a role in different aspects of mitochondrial physiology, including mitochondrial dynamics, oxidative stress processes, and mitochondrial transport along the axons. Disruption of the mitochondrial network in a neuroblastoma model of GDAP1-related CMT has been shown to decrease Ca2+ entry through the store-operated calcium entry (SOCE), which caused a failure in stimulation of mitochondrial respiration. In this review, we summarize the different functions proposed for GDAP1 and focus on the consequences for Ca2+ homeostasis and mitochondrial energy production linked to CMT disease caused by different GDAP1 mutations.

Hyaline fibromatosis syndrome: Clinical update and phenotype-genotype correlations.

Hyaline fibromatosis syndrome (HFS) is the unifying term for infantile systemic hyalinosis and juvenile hyaline fibromatosis. HFS is a rare autosomal recessive disorder of the connective tissue caused by mutations in the gene for anthrax toxin receptor-2 (ANTXR2). It is characterized by abnormal growth of hyalinized fibrous tissue with cutaneous, mucosal, osteoarticular, and systemic involvement. We reviewed the 84 published cases and their molecular findings, aiming to gain insight into the clinical features, prognostic factors, and phenotype-genotype correlations. Extreme pain at minimal handling in a newborn is the presentation pattern most frequently seen in grade 4 patients (life-limiting disease). Gingival hypertrophy and subcutaneous nodules are some of the disease hallmarks. Though painful joint stiffness and contractures are almost universal, weakness and hypotonia may also be present. Causes of death are intractable diarrhea, recurrent infections, and organ failure. Median age of death of grade 4 cases is 15.0 months (p25-p75: 9.5-24.0). This review provides evidence to reinforce the previous hypothesis that missense mutations in exons 1-12 and mutations leading to a premature stop codon lead to the severe form of the disease, while missense pathogenic variants in exons 13-17 lead to the mild form of the disease. Multidisciplinary team approach is recommended.

Cerebrospinal fluid monoamines, pterins, and folate in patients with mitochondrial diseases: systematic review and hospital experience.

Mitochondrial diseases are a group of genetic disorders leading to the dysfunction of mitochondrial energy metabolism pathways. We aimed to assess the clinical phenotype and the biochemical cerebrospinal fluid (CSF) biogenic amine profiles of patients with different diagnoses of genetic mitochondrial diseases. We recruited 29 patients with genetically confirmed mitochondrial diseases harboring mutations in either nuclear or mitochondrial DNA (mtDNA) genes. Signs and symptoms of impaired neurotransmission and neuroradiological data were recorded. CSF monoamines, pterins, and 5-methyltetrahydrofolate (5MTHF) concentrations were analyzed using high-performance liquid chromatography with electrochemical and fluorescence detection procedures. The mtDNA mutations were studied by Sanger sequencing, Southern blot, and real-time PCR, and nuclear DNA was assessed either by Sanger or next-generation sequencing. Five out of 29 cases showed predominant dopaminergic signs not attributable to basal ganglia involvement, harboring mutations in different nuclear genes. A chi-square test showed a statistically significant association between high homovanillic acid (HVA) values and low CSF 5-MTHF values (chi-square = 10.916; p = 0.001). Seven out of the eight patients with high CSF HVA values showed cerebral folate deficiency. Five of them harbored mtDNA deletions associated with Kearns-Sayre syndrome (KSS), one had a mitochondrial point mutation at the mtDNA ATPase6 gene, and one had a POLG mutation. In conclusion, dopamine deficiency clinical signs were present in some patients with mitochondrial diseases with different genetic backgrounds. High CSF HVA values, together with a severe cerebral folate deficiency, were observed in KSS patients and in other mtDNA mutation syndromes.

Lack of GDAP1 induces neuronal calcium and mitochondrial defects in a knockout mouse model of charcot-marie-tooth neuropathy.

Mutations in GDAP1, which encodes protein located in the mitochondrial outer membrane, cause axonal recessive (AR-CMT2), axonal dominant (CMT2K) and demyelinating recessive (CMT4A) forms of Charcot-Marie-Tooth (CMT) neuropathy. Loss of function recessive mutations in GDAP1 are associated with decreased mitochondrial fission activity, while dominant mutations result in impairment of mitochondrial fusion with increased production of reactive oxygen species and susceptibility to apoptotic stimuli. GDAP1 silencing in vitro reduces Ca2+ inflow through store-operated Ca2+ entry (SOCE) upon mobilization of endoplasmic reticulum (ER) Ca2+, likely in association with an abnormal distribution of the mitochondrial network. To investigate the functional consequences of lack of GDAP1 in vivo, we generated a Gdap1 knockout mouse. The affected animals presented abnormal motor behavior starting at the age of 3 months. Electrophysiological and biochemical studies confirmed the axonal nature of the neuropathy whereas histopathological studies over time showed progressive loss of motor neurons (MNs) in the anterior horn of the spinal cord and defects in neuromuscular junctions. Analyses of cultured embryonic MNs and adult dorsal root ganglia neurons from affected animals demonstrated large and defective mitochondria, changes in the ER cisternae, reduced acetylation of cytoskeletal α-tubulin and increased autophagy vesicles. Importantly, MNs showed reduced cytosolic calcium and SOCE response. The development and characterization of the GDAP1 neuropathy mice model thus revealed that some of the pathophysiological changes present in axonal recessive form of the GDAP1-related CMT might be the consequence of changes in the mitochondrial network biology and mitochondria-endoplasmic reticulum interaction leading to abnormalities in calcium homeostasis.