Choline transporter-like 1 deficiency causes a new type of childhood-onset neurodegeneration.

Cerebral choline metabolism is crucial for normal brain function, and its homoeostasis depends on carrier-mediated transport. Here, we report on four individuals from three families with neurodegenerative disease and homozygous frameshift mutations (Asp517Metfs*19, Ser126Metfs*8, and Lys90Metfs*18) in the SLC44A1 gene encoding choline transporter-like protein 1. Clinical features included progressive ataxia, tremor, cognitive decline, dysphagia, optic atrophy, dysarthria, as well as urinary and bowel incontinence. Brain MRI demonstrated cerebellar atrophy and leukoencephalopathy. Moreover, low signal intensity in globus pallidus with hyperintensive streaking and low signal intensity in substantia nigra were seen in two individuals. The Asp517Metfs*19 and Ser126Metfs*8 fibroblasts were structurally and functionally indistinguishable. The most prominent ultrastructural changes of the mutant fibroblasts were reduced presence of free ribosomes, the appearance of elongated endoplasmic reticulum and strikingly increased number of mitochondria and small vesicles. When chronically treated with choline, those characteristics disappeared and mutant ultrastructure resembled healthy control cells. Functional analysis revealed diminished choline transport yet the membrane phosphatidylcholine content remained unchanged. As part of the mechanism to preserve choline and phosphatidylcholine, choline transporter deficiency was implicated in impaired membrane homeostasis of other phospholipids. Choline treatments could restore the membrane lipids, repair cellular organelles and protect mutant cells from acute iron overload. In conclusion, we describe a novel childhood-onset neurometabolic disease caused by choline transporter deficiency with autosomal recessive inheritance.

MPV17 mutations in juvenile- and adult-onset axonal sensorimotor polyneuropathy.

MPV17 encodes a putative channel-forming protein of the inner mitochondrial membrane and is involved in mitochondrial deoxynucleotide homeostasis. MPV17 mutations were first reported in patients with Navajo neurohepatopathy, an autosomal recessive mitochondrial DNA depletion syndrome, characterized by early-onset liver failure, failure to thrive as well as central and peripheral neurological involvement. Recently, two patients with juvenile-onset peripheral sensorimotor neuropathy associated with an MVP17 c.122G>A (p.Arg41Gln) variant have been reported. Here, we describe five additional patients from two unrelated families with sensorimotor axonal neuropathy without hepatocerebral affection caused by homozygous MPV17 variants. Patients of the first family carried the known c.122G>A variant and affected individuals of the second family had a novel c.376-9T>G near-splice variant, which was shown to result in an in-frame deletion of 11 amino acids. This report provides further evidence that MPV17 mutations should be considered in patients with pure, non-syndromic axonal neuropathy.

SYNE1 ataxia is a common recessive ataxia with major non-cerebellar features: a large multi-centre study.

Mutations in the synaptic nuclear envelope protein 1 (SYNE1) gene have been reported to cause a relatively pure, slowly progressive cerebellar recessive ataxia mostly identified in Quebec, Canada. Combining next-generation sequencing techniques and deep-phenotyping (clinics, magnetic resonance imaging, positron emission tomography, muscle histology), we here established the frequency, phenotypic spectrum and genetic spectrum of SYNE1 in a screening of 434 non-Canadian index patients from seven centres across Europe. Patients were screened by whole-exome sequencing or targeted panel sequencing, yielding 23 unrelated families with recessive truncating SYNE1 mutations (23/434 = 5.3%). In these families, 35 different mutations were identified, 34 of them not previously linked to human disease. While only 5/26 patients (19%) showed the classical SYNE1 phenotype of mildly progressive pure cerebellar ataxia, 21/26 (81%) exhibited additional complicating features, including motor neuron features in 15/26 (58%). In three patients, respiratory dysfunction was part of an early-onset multisystemic neuromuscular phenotype with mental retardation, leading to premature death at age 36 years in one of them. Positron emission tomography imaging confirmed hypometabolism in extra-cerebellar regions such as the brainstem. Muscle biopsy reliably showed severely reduced or absent SYNE1 staining, indicating its potential use as a non-genetic indicator for underlying SYNE1 mutations. Our findings, which present the largest systematic series of SYNE1 patients and mutations outside Canada, revise the view that SYNE1 ataxia causes mainly a relatively pure cerebellar recessive ataxia and that it is largely limited to Quebec. Instead, complex phenotypes with a wide range of extra-cerebellar neurological and non-neurological dysfunctions are frequent, including in particular motor neuron and brainstem dysfunction. The disease course in this multisystemic neurodegenerative disease can be fatal, including premature death due to respiratory dysfunction. With a relative frequency of ∼5%, SYNE1 is one of the more common recessive ataxias worldwide.

Pantethine treatment is effective in recovering the disease phenotype induced by ketogenic diet in a pantothenate kinase-associated neurodegeneration mouse model.

Pantothenate kinase-associated neurodegeneration, caused by mutations in the PANK2 gene, is an autosomal recessive disorder characterized by dystonia, dysarthria, rigidity, pigmentary retinal degeneration and brain iron accumulation. PANK2 encodes the mitochondrial enzyme pantothenate kinase type 2, responsible for the phosphorylation of pantothenate or vitamin B5 in the biosynthesis of co-enzyme A. A Pank2 knockout (Pank2(-/-)) mouse model did not recapitulate the human disease but showed azoospermia and mitochondrial dysfunctions. We challenged this mouse model with a low glucose and high lipid content diet (ketogenic diet) to stimulate lipid use by mitochondrial beta-oxidation. In the presence of a shortage of co-enzyme A, this diet could evoke a general impairment of bioenergetic metabolism. Only Pank2(-/-) mice fed with a ketogenic diet developed a pantothenate kinase-associated neurodegeneration-like syndrome characterized by severe motor dysfunction, neurodegeneration and severely altered mitochondria in the central and peripheral nervous systems. These mice also showed structural alteration of muscle morphology, which was comparable with that observed in a patient with pantothenate kinase-associated neurodegeneration. We here demonstrate that pantethine administration can prevent the onset of the neuromuscular phenotype in mice suggesting the possibility of experimental treatment in patients with pantothenate kinase-associated neurodegeneration.

PNPLA6 mutations cause Boucher-Neuhauser and Gordon Holmes syndromes as part of a broad neurodegenerative spectrum.

Boucher-Neuhäuser and Gordon Holmes syndromes are clinical syndromes defined by early-onset ataxia and hypogonadism plus chorioretinal dystrophy (Boucher-Neuhäuser syndrome) or brisk reflexes (Gordon Holmes syndrome). Here we uncover the genetic basis of these two syndromes, demonstrating that both clinically distinct entities are allelic for recessive mutations in the gene PNPLA6. In five of seven Boucher-Neuhäuser syndrome/Gordon Holmes syndrome families, we identified nine rare conserved and damaging mutations by applying whole exome sequencing. Further, by dissecting the complex clinical presentation of Boucher-Neuhäuser syndrome and Gordon Holmes syndrome into its neurological system components, we set out to analyse an additional 538 exomes from families with ataxia (with and without hypogonadism), pure and complex hereditary spastic paraplegia, and Charcot-Marie-Tooth disease type 2. We identified four additional PNPLA6 mutations in spastic ataxia and hereditary spastic paraplegia families, revealing that Boucher-Neuhäuser and Gordon Holmes syndromes in fact represent phenotypic clusters on a spectrum of neurodegenerative diseases caused by mutations in PNPLA6. Structural analysis indicates that the majority of mutations falls in the C-terminal phospholipid esterase domain and likely inhibits the catalytic activity of PNPLA6, which provides the precursor for biosynthesis of the neurotransmitter acetylcholine. Our findings show that PNPLA6 influences a manifold of neuronal systems, from the retina to the cerebellum, upper and lower motor neurons and the neuroendocrine system, with damage of this protein causing an extraordinarily broad continuous spectrum of associated neurodegenerative disease.

Long-Term Observations in an Affected Family with Neurogenic Scapuloperoneal Syndrome Caused by Mutation R269C in the TRPV4 Gene.

Mutations in the TRPV4 gene, encoding a polymodal Ca(2+) permeable channel, are causative for several human diseases, affecting the skeletal and the peripheral nervous system with highly variable phenotypes. We report on a family with two affected individuals. The father clinically suffered from a classical scapuloperoneal syndrome, while the son presented with a severe neonatal onset with congenital respiratory distress, feeding problems and arthrogryposis multiplex. Multi-Gene Panel sequencing by next generation sequencing revealed the heterozygous mutation c.805C>T (p.R269C) in the TRPV4 gene. Long-term observation over two decades showed no relevant disease progression in the father and, after a dramatic neonatal period, a significant improvement in the son who became ambulant with orthoses at the age of 5 years, suggesting a reasonably good prognosis even in cases with severe neonatal onset. Long-term findings in muscle ultrasound correlated with the clinical course, showing stable or even slightly improved findings. Neurography revealed a late-onset sensory neuropathy in the father, which was so far not described in TRPV4 neuropathies.

Nerve conduction studies in spastic paraplegia, optic atrophy, and neuropathy (SPOAN) syndrome.

INTRODUCTION: SPOAN (spastic paraplegia, optic atrophy, and neuropathy) syndrome is an autosomal recessive neurodegenerative disorder identified in a large consanguineous Brazilian family. METHODS: Twenty-seven patients with SPOAN syndrome (20 women), aged 4-58 years, underwent nerve conduction studies (NCS) of the median, ulnar, tibial, and fibular nerves, and sensory NCS of the median, ulnar, radial, sural, and superficial fibular nerves. RESULTS: Sensory nerve action potentials were absent in the lower limbs and absent in >80% of upper limbs. Motor NCS had reduced amplitudes and borderline velocities in the upper limbs and absent compound muscle action potentials (CMAPs) in the lower limbs. CONCLUSIONS: The neuropathy in SPOAN syndrome is a severe, early-onset sensory-motor axonal polyneuropathy. Normal NCS seem to rule-out this condition.

Mitochondrial protein associated neurodegeneration - case report.

Neurodegeneration with brain iron accumulation (NBIA) is a group of genetic disorders with a progressive extrapyramidal syndrome and excessive iron deposition in the brain, particularly in the globus pallidus and substantia nigra. We present the case of a 31-year-old woman with mitochondrial protein associated neurodegeneration (MPAN). MPAN is a new identified subtype of NBIA, caused by mutations in C19orf12 gene. The typical features are speech and gait disturbances, dystonia, parkinsonism and pyramidal signs. Common are psychiatric symptoms such as impulsive or compulsive behavior, depression and emotional lability. In almost all cases, the optic atrophy has been noted and about 50% of cases have had a motor axonal neuropathy. In the MRI on T2- and T2*-weighted images, there are hypointense lesions in the globus palidus and substantia nigra corresponding to iron accumulation.

Huntington's disease and Huntington's disease-like syndromes: an overview.

PURPOSE OF REVIEW: The differential diagnosis of chorea syndromes may be complex and includes various genetic disorders such as Huntington's disease and mimicking disorders called Huntington's disease-like (HDL) phenotypes. To familiarize clinicians with these (in some cases very rare) conditions we will summarize the main characteristics. RECENT FINDINGS: HDL disorders are rare and account for about 1% of cases presenting with a Huntington's disease phenotype. They share overlapping clinical features, so making the diagnosis purely on clinical grounds may be challenging, however presence of certain characteristics may be a clue (e.g. prominent orofacial involvement in neuroferritinopathy etc.), Information of ethnic descent will also guide genetic work-up [HDL2 in Black Africans; dentatorubral-pallidoluysian atrophy (DRPLA) in Japanese etc.], Huntington's disease, the classical HDL disorders (except HDL3) and DRPLA are repeat disorders with anticipation effect and age-dependent phenotype in some, but genetic underpinnings may be more complicated in the other chorea syndromes. SUMMARY: With advances in genetics more and more rare diseases are disentangled, allowing molecular diagnoses in a growing number of choreic patients. Hopefully, with better understanding of their pathophysiology we are moving towards mechanistic therapies.

Disruption of Cnp1 uncouples oligodendroglial functions in axonal support and myelination.

Myelination of axons by oligodendrocytes enables rapid impulse propagation in the central nervous system. But long-term interactions between axons and their myelin sheaths are poorly understood. Here we show that Cnp1, which encodes 2',3'-cyclic nucleotide phosphodiesterase in oligodendrocytes, is essential for axonal survival but not for myelin assembly. In the absence of glial cyclic nucleotide phosphodiesterase, mice developed axonal swellings and neurodegeneration throughout the brain, leading to hydrocephalus and premature death. But, in contrast to previously studied myelin mutants, the ultrastructure, periodicity and physical stability of myelin were not altered in these mice. Genetically, the chief function of glia in supporting axonal integrity can thus be completely uncoupled from its function in maintaining compact myelin. Oligodendrocyte dysfunction, such as that in multiple sclerosis lesions, may suffice to cause secondary axonal loss.

RNA-mediated neurodegeneration in repeat expansion disorders.

Most neurodegenerative disorders are thought to result primarily from the accumulation of misfolded proteins, which interfere with protein homeostasis in neurons. For a subset of diseases, however, noncoding regions of RNAs assume a primary toxic gain-of-function, leading to degeneration in many tissues, including the nervous system. Here we review a series of proposed mechanisms by which noncoding repeat expansions give rise to nervous system degeneration and dysfunction. These mechanisms include transcriptional alterations and the generation of antisense transcripts, sequestration of mRNA-associated protein complexes that lead to aberrant mRNA splicing and processing, and alterations in cellular processes, including activation of abnormal signaling cascades and failure of protein quality control pathways. We place these potential mechanisms in the context of known RNA-mediated disorders, including the myotonic dystrophies and fragile X tremor ataxia syndrome, and discuss recent results suggesting that mRNA toxicity may also play a role in some presumably protein-mediated neurodegenerative disorders. Lastly, we comment on recent progress in therapeutic development for these RNA-dominant diseases.

CAG repeat RNA as an auxiliary toxic agent in polyglutamine disorders.

Over 20 genetic loci with abnormal expansions of short tandem repeats have been associated with human hereditary neurological diseases. Of these, specific trinucleotide repeats located in non-coding and coding regions of individual genes implicated in these disorders are strongly overrepresented. Expansions of CTG, CGG and CAG repeats are linked to, respectively, myotonic dystrophy type 1 (DM1), fragile X-associated tremor/ataxia syndrome (FXTAS), as well as Huntington's disease (HD) and a number of spinocerebellar ataxias (SCAs). Expanded CAG repeats in translated exons trigger the most disorders for which a protein gain-of-function mechanism has been proposed to explain neurodegeneration by polyglutamine-rich (poly-Q) proteins. However, the results of last years showed that RNA composed of mutated CAG repeats can also be toxic and contribute to pathogenesis of polyglutamine disorders through an RNA-mediated gain-of-function mechanism. This mechanism has been best characterized in the non-coding repeat disorder DM1 and is also implicated in several other diseases, such as FXTAS, spinocerebellar ataxia type 8 (SCA8), Huntington's disease-like 2 (HDL2), as well as in myotonic dystrophy type 2 (DM2), spinocerebellar ataxia type 10 (SCA10) and type 31 (SCA31). In this review, we summarize recent findings that emphasize the participation of coding mutant CAG repeat RNA in the pathogenesis of polyglutamine disorders, and we discuss the basis of an RNA gain-of-function model in non-coding diseases such as DM1, FXTAS and SCA8.

Involuntary moaning in a Hispanic family with eight affected members.

Involuntary moaning has been reported in sporadic cases of neurodegenerative diseases. A five-generation Hispanic family with eight members exhibiting involuntary moaning, most of whom with isolated moaning in the absence of any additional neurological disorder carried a missense variant in the NEFH gene segregating in the family.

Epigenetic changes and non-coding expanded repeats.

Many neurogenetic disorders are caused by unstable expansions of tandem repeats. Some of the causal mutations are located in non-protein-coding regions of genes. When pathologically expanded, these repeats can trigger focal epigenetic changes that repress the expression of the mutant allele. When the mutant gene is not repressed, the transcripts containing the expanded repeat can give rise to a toxic gain-of-function by the mutant RNA. These two mechanisms, heterochromatin-mediated gene repression and RNA dominance, produce a wide range of neurodevelopmental and neurodegenerative abnormalities. Here we review the mechanisms of gene dysregulation induced by non-coding repeat expansions, and early indications that some of these disorders may prove to be responsive to therapeutic intervention.

Mitochondrial complex I deficiency: from organelle dysfunction to clinical disease.

Mitochondria are essential for cellular bioenergetics by way of energy production in the form of ATP through the process of oxidative phosphorylation. This crucial task is executed by five multi-protein complexes of which mitochondrial NADH:ubiquinone oxidoreductase or complex I is the largest and most complicated one. During recent years, mutations in nuclear genes encoding structural subunits of complex I have been identified as a cause of devastating neurodegenerative disorders with onset in early childhood. Here, we present a comprehensive overview of clinical, biochemical and cell physiological information of 15 children with isolated, nuclear-encoded complex I deficiency, which was generated in a joint effort of clinical and fundamental research. Our findings point to a rather homogeneous clinical picture in these children and drastically illustrate the severity of the disease. In extensive live cell studies with patient-derived skin fibroblasts we uncovered important cell physiological aspects of complex I deficiency, which point to a central regulatory role of cellular reactive oxygen species production and altered mitochondrial membrane potential in the pathogenesis of the disorder. Moreover, we critically discuss possible interconnections between clinical signs and cellular pathology. Finally, our results indicate apparent differences to drug therapy on the cellular level, depending on the severity of the catalytic defect and identify modulators of cellular Ca(2+) homeostasis as new candidates in the therapy of complex I deficiency.

[Neurodegenerative polyglutamine expansion diseases: physiopathology and therapeutic strategies]. / Les maladies neurodégénératives par expansion de polyglutamine: physiopathologie et stratégies thérapeutiques.

Polyglutamine expansion diseases are adult-onset inherited neurodegenerative disorders that lead to death 10 to 20 years after the first symptoms. Currently, there is no therapy to fight against these diseases. They include Huntington's disease, spinobulbar muscular atrophy, dentatorubral-pallido-luysian atrophy and six types of spino-cerebellar ataxia. The diseases are caused by a unique mutational mechanism: an expansion of the CAG trinucleotide in the corresponding genes coding for an expanded tract of glutamine in the mutated proteins. Polyglutamine expansion confers to the mutant proteins toxic properties that cause neuronal cell death in brain regions specific to each disease. Thanks to cellular and animal models (fly, fish, mouse and rat) of these diseases, we have considerably improved our understanding of the toxic nature of polyglutamine expansion and the physiopathology, and we are now in position to design and test therapeutic strategies to prevent or delay the disease process.

The neuropsychological deficits and dissociations in Huntington Disease-Like 2: A series of case-control studies.

OBJECTIVES: Huntington's Disease Like-2 (HDL2) is a rare autosomal dominant genetic disease caused by a mutation in the JPH3 gene. The Huntington's Disease (HD) phenocopy has the greatest clinical resemblance to HD, but its neurocognitive characterisation is poorly researched. This study reports on the neurocognitive profile of seven HDL2 patients including preserved functions, deficits and dissociations (classical and strong) and provides a general characterisation of the cognitive dysfunction of HDL2 in relation to the progression of the disease. METHODS: The neuropsychological performance of seven HDL2 patients were compared to one of four control groups, matched by age and level of education using a Single Case-Control design. All patients were polyglots and with public education (primary and secondary). Deficits, as well as classical and strong dissociations within each case profile, were identified by implementing Crawford and Howell's (1998) t-test and the Revised Standardized Difference Test (Crawford and Garthwaite, 2005), respectively. RESULTS: The HDL2 neurocognitive syndrome is heterogeneous with a variable rate of progression, with the psychomotor and dexterity domain consistently and severely impaired. CONCLUSION: HDL2 has a heterogeneous impact on cognitive functions from early stages in the disease, which evolve to dementia in a non-uniform manner, in keeping with preferential damage in the cerebrocortical-basal ganglia-thalamus-cerebrocortical circuit.

The Neuropsychiatry of Huntington Disease-Like 2: A Comparison with Huntington's Disease.

BACKGROUND: Huntington Disease-Like 2 (HDL2) is a rare autosomal dominant disorder caused by an abnormal CAG/CTG triplet repeat expansion on chromosome 16q24. The symptoms of progressive decline in motor, cognitive and psychiatric functioning are similar to those of Huntington's disease (HD). The psychiatric features of the HDL2 have been poorly characterized. OBJECTIVE: To describe the neuropsychiatric features of HDL2 and compare them with those of HD. METHODS: A blinded cross-sectional design was used to compare the behavioural component of the Unified Huntington's Disease Rating Scale (UHDRS) in participants with HDL2 (n = 15) and HD (n = 13) with African ancestry. RESULTS: HDL2 patients presented with psychiatric symptoms involving mood disturbances and behavioural changes that were not significantly different from those in the HD group. Duration of disease and motor performance correlated (p < 0.001) with the Functional Capacity score and the Independence score of the UHDRS. HD patients reported movement dysfunction as the first symptom more frequently than HDL2 Patients (p < 0.001). CONCLUSION: The psychiatric phenotype of HDL2 is similar to that of HD and linked to motor decline and disease duration. Psychiatric symptoms seem more severe for HDL2 patients in the early stages of the disease.

Blended phenotype of AP4E1 deficiency and Angelman syndrome caused by paternal isodisomy of chromosome 15.

Atypical phenotype of an imprinting disease can develop with a recessive homozygous variant due to uniparental isodisomy. We present a girl with severe intellectual disability, developmental delay, distinctive facial features, and other neuropsychiatric features. Trio whole exome sequencing revealed a novel homozygous frameshift variant in AP4E1 [NM_007347.5:c.2412dupT:p.(Gly805Trpfs*8)] and uniparental isodisomy of chromosome 15 [iUPD(15)]. Single nucleotide polymorphism mapping analysis of exome data showed that the homozygous AP4E1 variant was derived from her heterozygous carrier father and unmasked by paternal iUPD(15). Brain magnetic resonance imaging confirmed the brain abnormalities characteristic of AP4 deficiency including the dilated ventricles and hypointensity in the globus pallidus in susceptibility-weighted imaging. This is the first case report of a combination of AP4E1 deficiency and Angelman syndrome. Our patient indicates that whole exome sequencing could uncover an atypical phenotype caused by multiple genetic factors including the uniparental isodisomy.

Charcot-Marie-Tooth Disease and Other Hereditary Neuropathies.

PURPOSE OF REVIEW: This article provides an overview of Charcot-Marie-Tooth disease (CMT) and other inherited neuropathies. These disorders encompass a broad spectrum with variable motor, sensory, autonomic, and other organ system involvement. Considerable overlap exists, both phenotypically and genetically, among these separate categories, all eventually exhibiting axonal injury and neurologic impairment. Depending on the specific neural and non-neural localizations, patients experience varying morbidity and mortality. Neurologic evaluations, including neurophysiologic testing, can help diagnose and predict patient disabilities. Diagnosis is often complex, especially when genetic and acquired components overlap. RECENT FINDINGS: Next-generation sequencing has greatly improved genetic diagnosis, with many third-party reimbursement parties now embracing phenotype-based panel evaluations. Through the advent of comprehensive gene panels, symptoms previously labeled as idiopathic or atypical now have a better chance to receive a specific diagnosis. A definitive molecular diagnosis affords patients improved care and counsel. The new classification scheme for inherited neuropathies emphasizes the causal gene names. A specific genetic diagnosis is important as considerable advances are being made in gene-specific therapeutics. Emerging therapeutic approaches include small molecule chaperones, antisense oligonucleotides, RNA interference, and viral gene delivery therapies. New therapies for hereditary transthyretin amyloidosis and Fabry disease are discussed. SUMMARY: Comprehensive genetic testing through a next-generation sequencing approach is simplifying diagnostic algorithms and affords significantly improved decision-making processes in neuropathy care. Genetic diagnosis is essential for pathogenic understanding and for gene therapy development. Gene-targeted therapies have begun entering the clinic. Currently, for most inherited neuropathy categories, specific symptomatic management and family counseling remain the mainstays of therapy.