RESUMEN
PURPOSE: We describe 3 families with Charcot-Marie-Tooth neuropathy (CMT), harboring a homozygous NDUFS6 NM_004553.6:c.309+5G>A variant previously linked to fatal Leigh syndrome. We aimed to characterize clinically and molecularly the newly identified patients and understand the mechanism underlying their milder phenotype. METHODS: The patients underwent extensive clinical examinations. Exome sequencing was done in 4 affected individuals. The functional effect of the c.309+5G>A variant was investigated in patient-derived EBV-transformed lymphoblasts at the complementary DNA, protein, and mitochondrial level. Alternative splicing was evaluated using complementary DNA long-read sequencing. RESULTS: All patients presented with early-onset, slowly progressive axonal CMT, and nystagmus; some exhibited additional central nervous system symptoms. The c.309+5G>A substitution caused the expression of aberrantly spliced transcripts and negligible levels of the canonical transcript. Immunoblotting showed reduced levels of mutant isoforms. No detectable defects in mitochondrial complex stability or bioenergetics were found. CONCLUSION: We expand the clinical spectrum of NDUFS6-related mitochondrial disorders to include axonal CMT, emphasizing the clinical and pathophysiologic overlap between these 2 clinical entities. This work demonstrates the critical role that alternative splicing may play in modulating the severity of a genetic disorder, emphasizing the need for careful consideration when interpreting splice variants and their implications on disease prognosis.
Asunto(s)
Empalme Alternativo , Enfermedad de Charcot-Marie-Tooth , Enfermedades Mitocondriales , Humanos , Empalme Alternativo/genética , Masculino , Femenino , Enfermedad de Charcot-Marie-Tooth/genética , Enfermedad de Charcot-Marie-Tooth/patología , Enfermedades Mitocondriales/genética , Enfermedades Mitocondriales/patología , Niño , NADH Deshidrogenasa/genética , Linaje , Mutación/genética , Fenotipo , Secuenciación del Exoma , Enfermedad de Leigh/genética , Enfermedad de Leigh/patología , Mitocondrias/genética , Mitocondrias/patología , Complejo I de Transporte de Electrón/genética , Adulto , Preescolar , AdolescenteRESUMEN
OBJECTIVE: To identify the unknown genetic cause in a large pedigree previously classified with a distinct form of axonal Charcot-Marie-Tooth disease type 2G (CMT2G) and to explore its transcriptional consequences. METHODS: Clinical reevaluation of the pedigree was performed, followed by linkage analysis with the redefined disease statuses, and whole genome and exome sequencing. The impact of the mutation was investigated by immunoblotting and transcriptome sequencing. RESULTS: Thirteen affected individuals over 3 generations displayed mild and quiescent lower-limb axonal sensorimotor neuropathy. Magnetic resonance imaging (MRI) of lower-limb musculature systematically showed fatty atrophy in clinical and subclinical mutation carriers. We redefined the disease-linked region to chr9q31.3-q34.2 and subsequently identified a novel missense variant in the E3 ubiquitin-protein ligase LRSAM1 (p.Cys694Tyr). Unlike previous reports, we demonstrated in patients' lymphoblasts that the mutation does not influence overall protein levels of LRSAM1, nor of its ubiquitylation target TSG101. The mutation is associated with several transcriptional changes, including a significant upregulation of another E3 ubiquitin-protein ligase, NEDD4L, and of TNFRSF21, a key regulator of axonal degeneration. INTERPRETATION: Our findings demonstrate that the isolated genetic entity CMT2G is caused by a missense mutation in LRSAM1 and should be reclassified as CMT2P. MRI of lower-limb musculature can be used to detect minimal signs of the disease. Transcriptome analysis of patients' cells highlights novel molecular players associated with LRSAM1 dysfunction, and reveals pathways and therapeutic targets shared with amyotrophic lateral sclerosis and Alzheimer disease. Ann Neurol 2016;80:823-833.
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Enfermedad de Charcot-Marie-Tooth/genética , Complejos de Clasificación Endosomal Requeridos para el Transporte/metabolismo , Receptores del Factor de Necrosis Tumoral/metabolismo , Ubiquitina-Proteína Ligasas/genética , Ubiquitina-Proteína Ligasas/metabolismo , Adulto , Anciano , Anciano de 80 o más Años , Femenino , Secuenciación de Nucleótidos de Alto Rendimiento , Humanos , Imagen por Resonancia Magnética , Masculino , Persona de Mediana Edad , Mutación Missense , Ubiquitina-Proteína Ligasas Nedd4 , Conducción Nerviosa/genética , Conducción Nerviosa/fisiología , Linaje , Regulación hacia ArribaRESUMEN
We performed whole exome sequencing on a patient with Charcot-Marie-Tooth disease type 1 and identified a de novo mutation in PMP2, the gene that encodes the myelin P2 protein. This mutation (p.Ile52Thr) was passed from the proband to his one affected son, and segregates with clinical and electrophysiological evidence of demyelinating neuropathy. We then screened a cohort of 136 European probands with uncharacterized genetic cause of Charcot-Marie-Tooth disease and identified another family with Charcot-Marie-Tooth disease type 1 that has a mutation affecting an adjacent amino acid (p.Thr51Pro), which segregates with disease. Our genetic and clinical findings in these kindred demonstrate that dominant PMP2 mutations cause Charcot-Marie-Tooth disease type 1.
Asunto(s)
Enfermedad de Charcot-Marie-Tooth/genética , Proteína P2 de Mielina/genética , Adolescente , Exoma/genética , Femenino , Predisposición Genética a la Enfermedad/genética , Haplotipos , Humanos , Masculino , Persona de Mediana Edad , Mutación , Conducción Nerviosa/genética , Linaje , Adulto JovenRESUMEN
The most common form of spinal muscular atrophy (SMA) is a recessive disorder caused by deleterious SMN1 mutations in 5q13, whereas the genetic etiologies of non-5q SMA are very heterogeneous and largely remain to be elucidated. In a Bulgarian family affected by autosomal-dominant proximal SMA, we performed genome-wide linkage analysis and whole-exome sequencing and found a heterozygous de novo c.320C>T (p.Ser107Leu) mutation in bicaudal D homolog 2 (Drosophila) (BICD2). Further analysis of BICD2 in a cohort of 119 individuals with non-5q SMA identified a second de novo BICD2 mutation, c.2321A>G (p.Glu774Gly), in a simplex case. Detailed clinical and electrophysiological investigations revealed that both families are affected by a very similar disease course, characterized by early childhood onset, predominant involvement of lower extremities, and very slow disease progression. The amino acid substitutions are located in two interaction domains of BICD2, an adaptor protein linking the dynein molecular motor with its cargo. Our immunoprecipitation and localization experiments in HeLa and SH-SY5Y cells and affected individuals' lymphoblasts demonstrated that p.Ser107Leu causes increased dynein binding and thus leads to accumulation of BICD2 at the microtubule-organizing complex and Golgi fragmentation. In addition, the altered protein had a reduced colocalization with RAB6A, a regulator of vesicle trafficking between the Golgi and the endoplasmic reticulum. The interaction between p.Glu744Gly altered BICD2 and RAB6A was impaired, which also led to their reduced colocalization. Our study identifies BICD2 mutations as a cause of non-5q linked SMA and highlights the importance of dynein-mediated motility in motor neuron function in humans.
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Proteínas Portadoras/genética , Genes Dominantes , Atrofia Muscular Espinal/genética , Mutación Missense , Adulto , Secuencia de Bases , Proteínas Portadoras/metabolismo , Niño , Preescolar , Femenino , Estudios de Asociación Genética , Células HeLa , Humanos , Masculino , Proteínas Asociadas a Microtúbulos , Persona de Mediana Edad , Atrofia Muscular Espinal/metabolismo , Linaje , Transporte de Proteínas , Análisis de Secuencia de ADN , Adulto Joven , Proteínas de Unión al GTP rab/metabolismoRESUMEN
The heavy chain 1 of cytoplasmic dynein (DYNC1H1) is responsible for movement of the motor complex along microtubules and recruitment of dynein components. Mutations in DYNC1H1 are associated with spinal muscular atrophy (SMA), hereditary motor and sensory neuropathy (HMSN), cortical malformations, or a combination of these. Combining linkage analysis and whole-exome sequencing, we identified a novel dominant defect in the DYNC1H1 tail domain (c.1792C>T, p.Arg598Cys) causing axonal HMSN. Mutation analysis of the tail region in 355 patients identified a de novo mutation (c.791G>T, p.Arg264Leu) in an isolated SMA patient. Her phenotype was more severe than previously described, characterized by multiple congenital contractures and delayed motor milestones, without brain malformations. The mutations in DYNC1H1 increase the interaction with its adaptor BICD2. This relates to previous studies on BICD2 mutations causing a highly similar phenotype. Our findings broaden the genetic heterogeneity and refine the clinical spectrum of DYNC1H1, and have implications for molecular diagnostics of motor neuron diseases.
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Enfermedad de Charcot-Marie-Tooth/genética , Dineínas Citoplasmáticas/genética , Dineínas/metabolismo , Atrofia Muscular Espinal/genética , Mutación , Enfermedad de Charcot-Marie-Tooth/fisiopatología , Dineínas Citoplasmáticas/metabolismo , Humanos , Proteínas Asociadas a Microtúbulos/metabolismo , Atrofia Muscular Espinal/fisiopatología , Estructura Terciaria de Proteína/genéticaRESUMEN
Autosomal recessive forms of Charcot-Marie-Tooth disease (ARCMT) are rare but severe disorders of the peripheral nervous system. Their molecular basis is poorly understood due to the extensive genetic and clinical heterogeneity, posing considerable challenges for patients, physicians, and researchers. We report on the genetic findings from a systematic study of a large collection of 174 independent ARCMT families. Initial sequencing of the three most common ARCMT genes (ganglioside-induced differentiation protein 1GDAP1, SH3 domain and tetratricopeptide repeats-containing protein 2SH3TC2, histidine-triad nucleotide binding protein 1HINT1) identified pathogenic mutations in 41 patients. Subsequently, 87 selected nuclear families underwent single nucleotide polymorphism (SNP) genotyping and homozygosity mapping, followed by targeted screening of known ARCMT genes. This strategy provided molecular diagnosis to 22% of the families. Altogether, our unbiased genetic approach identified pathogenic mutations in ten ARCMT genes in a total of 41.3% patients. Apart from a newly described founder mutation in GDAP1, the majority of variants constitute private molecular defects. Since the gene testing was independent of the clinical phenotype of the patients, we identified mutations in patients with unusual or additional clinical features, extending the phenotypic spectrum of the SH3TC2 gene. Our study provides an overview of the ARCMT genetic landscape and proposes guidelines for tackling the genetic heterogeneity of this group of hereditary neuropathies.
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Enfermedad de Charcot-Marie-Tooth/diagnóstico , Enfermedad de Charcot-Marie-Tooth/genética , Mutación , Mapeo Cromosómico , Análisis Mutacional de ADN , Femenino , Genes Recesivos , Homocigoto , Humanos , Péptidos y Proteínas de Señalización Intracelular , Masculino , Proteínas del Tejido Nervioso/genética , Fenotipo , Polimorfismo de Nucleótido Simple , Proteínas/genéticaRESUMEN
Inherited peripheral neuropathies are a heterogeneous group of disorders that can affect patients of all ages. Children with inherited neuropathy often develop severe disability, but the genetic causes of recessive early-onset axonal neuropathies are not fully known. We have taken a whole-exome sequencing approach to identify causative disease mutations in single patients with early-onset axonal neuropathy. Here, we report compound heterozygous mutations in the tripartite motif containing 2 (TRIM2) gene in a patient with childhood-onset axonal neuropathy, low weight and small muscle mass. We show that the patient fibroblasts are practically devoid of TRIM2, through mRNA and protein instability caused by the mutations. TRIM2 is an E3 ubiquitin ligase that ubiquitinates neurofilament light chain, a component of the intermediate filament in axons. Resembling the findings in our patient's sural nerve biopsy, Trim2-gene trap mice showed axonopathy with accumulations of neurofilaments inside axons. Our results suggest that loss-of-function mutations in TRIM2 are a cause of axonal neuropathy, which we propose to develop as a consequence of axonal accumulation of neurofilaments, secondary to lack of its ubiquitination by TRIM2.
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Axones/metabolismo , Enfermedad de Charcot-Marie-Tooth/genética , Proteínas Nucleares/deficiencia , Adolescente , Axones/patología , Biopsia , Enfermedad de Charcot-Marie-Tooth/diagnóstico , Exoma , Femenino , Fibroblastos/metabolismo , Humanos , Mutación , Proteínas de Neurofilamentos/metabolismo , Estabilidad del ARN , Análisis de Secuencia de ADN , Nervio Sural/metabolismo , Nervio Sural/patologíaRESUMEN
Charcot-Marie-Tooth (CMT) neuropathies are common disorders of the peripheral nervous system caused by demyelination or axonal degeneration, or a combination of both features. We previously assigned the locus for autosomal dominant intermediate CMT neuropathy type C (DI-CMTC) to chromosome 1p34-p35. Here we identify two heterozygous missense mutations (G41R and E196K) and one de novo deletion (153-156delVKQV) in tyrosyl-tRNA synthetase (YARS) in three unrelated families affected with DI-CMTC. Biochemical experiments and genetic complementation in yeast show partial loss of aminoacylation activity of the mutant proteins, and mutations in YARS, or in its yeast ortholog TYS1, reduce yeast growth. YARS localizes to axonal termini in differentiating primary motor neuron and neuroblastoma cultures. This specific distribution is significantly reduced in cells expressing mutant YARS proteins. YARS is the second aminoacyl-tRNA synthetase found to be involved in CMT, thereby linking protein-synthesizing complexes with neurodegeneration.
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Axones/enzimología , Enfermedad de Charcot-Marie-Tooth/enzimología , Enfermedad de Charcot-Marie-Tooth/genética , Genes Dominantes/genética , Mutación/genética , Tirosina-ARNt Ligasa/genética , Tirosina-ARNt Ligasa/metabolismo , Secuencia de Aminoácidos , Animales , Axones/metabolismo , Axones/patología , Bioensayo , Células COS , Línea Celular Tumoral , Células Cultivadas , Enfermedad de Charcot-Marie-Tooth/metabolismo , Chlorocebus aethiops , Prueba de Complementación Genética , Heterocigoto , Humanos , Ratones , Datos de Secuencia Molecular , Transporte de Proteínas , Proteínas Recombinantes , Saccharomyces cerevisiae/citología , Saccharomyces cerevisiae/crecimiento & desarrollo , Alineación de Secuencia , Tirosina-ARNt Ligasa/químicaRESUMEN
Hereditary neuralgic amyotrophy (HNA) is an autosomal dominant recurrent neuropathy affecting the brachial plexus. HNA is triggered by environmental factors such as infection or parturition. We report three mutations in the gene septin 9 (SEPT9) in six families with HNA linked to chromosome 17q25. HNA is the first monogenetic disease caused by mutations in a gene of the septin family. Septins are implicated in formation of the cytoskeleton, cell division and tumorigenesis.
Asunto(s)
Neuritis del Plexo Braquial/genética , Cromosomas Humanos Par 17/genética , GTP Fosfohidrolasas/genética , Mutación , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Perros , Humanos , Ratones , Datos de Secuencia Molecular , Ratas , SeptinasRESUMEN
Defects in mitochondrial dynamics are a common cause of Charcot-Marie-Tooth disease (CMT), while primary deficiencies in the mitochondrial respiratory chain (MRC) are rare and atypical for this etiology. This study aims to report COX18 as a novel CMT-causing gene. This gene encodes an assembly factor of mitochondrial Complex IV (CIV) that translocates the C-terminal tail of MTCO2 across the mitochondrial inner membrane. Exome sequencing was performed in four affected individuals. The patients and available family members underwent thorough neurological and electrophysiological assessment. The impact of one of the identified variants on splicing, protein levels, and mitochondrial bioenergetics was investigated in patient-derived lymphoblasts. The functionality of the mutant protein was assessed using a Proteinase K protection assay and immunoblotting. Neuronal relevance of COX18 was assessed in a Drosophila melanogaster knockdown model. Exome sequencing coupled with homozygosity mapping revealed a homozygous splice variant c.435-6A>G in COX18 in two siblings with early-onset progressive axonal sensory-motor peripheral neuropathy. By querying external databases, we identified two additional families with rare deleterious biallelic variants in COX18 . All affected individuals presented with axonal CMT and some patients also exhibited central nervous system symptoms, such as dystonia and spasticity. Functional characterization of the c.435-6A>G variant demonstrated that it leads to the expression of an alternative transcript that lacks exon 2, resulting in a stable but defective COX18 isoform. The mutant protein impairs CIV assembly and activity, leading to a reduction in mitochondrial membrane potential. Downregulation of the COX18 homolog in Drosophila melanogaster displayed signs of neurodegeneration, including locomotor deficit and progressive axonal degeneration of sensory neurons. Our study presents genetic and functional evidence that supports COX18 as a newly identified gene candidate for autosomal recessive axonal CMT with or without central nervous system involvement. These findings emphasize the significance of peripheral neuropathy within the spectrum of primary mitochondrial disorders and the role of mitochondrial CIV in the development of CMT. Our research has important implications for the diagnostic workup of CMT patients.
RESUMEN
Genomic rearrangements involving the peripheral myelin protein gene (PMP22) in human chromosome 17p12 are associated with neuropathy: duplications cause Charcot-Marie-Tooth disease type 1A (CMT1A), whereas deletions lead to hereditary neuropathy with liability to pressure palsies (HNPP). Our previous studies showed that >99% of these rearrangements are recurrent and mediated by nonallelic homologous recombination (NAHR). Rare copy number variations (CNVs) generated by nonrecurrent rearrangements also exist in 17p12, but their underlying mechanisms are not well understood. We investigated 21 subjects with rare CNVs associated with CMT1A or HNPP by oligonucleotide-based comparative genomic hybridization microarrays and breakpoint sequence analyses, and we identified 17 unique CNVs, including two genomic deletions, ten genomic duplications, two complex rearrangements, and three small exonic deletions. Each of these CNVs includes either the entire PMP22 gene, or exon(s) only, or ultraconserved potential regulatory sequences upstream of PMP22, further supporting the contention that PMP22 is the critical gene mediating the neuropathy phenotypes associated with 17p12 rearrangements. Breakpoint sequence analysis reveals that, different from the predominant NAHR mechanism in recurrent rearrangement, various molecular mechanisms, including nonhomologous end joining, Alu-Alu-mediated recombination, and replication-based mechanisms (e.g., FoSTeS and/or MMBIR), can generate nonrecurrent 17p12 rearrangements associated with neuropathy. We document a multitude of ways in which gene function can be altered by CNVs. Given the characteristics, including small size, structural complexity, and location outside of coding regions, of selected rare CNVs, their identification remains a challenge for genome analysis. Rare CNVs may potentially represent an important portion of "missing heritability" for human diseases.
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Enfermedad de Charcot-Marie-Tooth/genética , Cromosomas Humanos Par 17 , Variaciones en el Número de Copia de ADN , Proteínas de la Mielina/genética , Parálisis/genética , Translocación Genética , Hibridación Genómica Comparativa , Eliminación de Gen , Duplicación de Gen , Neuropatía Hereditaria Motora y Sensorial , HumanosRESUMEN
Hereditary sensory and autonomic neuropathy type I (HSAN-I) is an axonal peripheral neuropathy associated with progressive distal sensory loss and severe ulcerations. Mutations in the first subunit of the enzyme serine palmitoyltransferase (SPT) have been associated with HSAN-I. The SPT enzyme catalyzes the first and rate-limiting step in the de novo sphingolipid synthesis pathway. However, different studies suggest the implication of other genes in the pathology of HSAN-I. Therefore, we screened the two other known subunits of SPT, SPTLC2 and SPTLC3, in a cohort of 78 HSAN patients. No mutations were found in SPTLC3, but we identified three heterozygous missense mutations in the SPTLC2 subunit of SPT in four families presenting with a typical HSAN-I phenotype. We demonstrate that these mutations result in a partial to complete loss of SPT activity in vitro and in vivo. Moreover, they cause the accumulation of the atypical and neurotoxic sphingoid metabolite 1-deoxy-sphinganine. Our findings extend the genetic heterogeneity in HSAN-I and enlarge the group of HSAN neuropathies associated with SPT defects. We further show that HSAN-I is consistently associated with an increased formation of the neurotoxic 1-deoxysphinganine, suggesting a common pathomechanism for HSAN-I.
Asunto(s)
Neuropatías Hereditarias Sensoriales y Autónomas/genética , Serina C-Palmitoiltransferasa/genética , Secuencia de Bases , Línea Celular , Clonación Molecular , Estudios de Cohortes , Análisis Mutacional de ADN , Cartilla de ADN/genética , Prueba de Complementación Genética , Humanos , Repeticiones de Microsatélite/genética , Datos de Secuencia Molecular , Mutación Missense/genética , Serina C-Palmitoiltransferasa/metabolismoRESUMEN
Distal hereditary motor neuropathies are pure motor disorders of the peripheral nervous system resulting in severe atrophy and wasting of distal limb muscles. In two pedigrees with distal hereditary motor neuropathy type II linked to chromosome 12q24.3, we identified the same mutation (K141N) in small heat-shock 22-kDa protein 8 (encoded by HSPB8; also called HSP22). We found a second mutation (K141E) in two smaller families. Both mutations target the same amino acid, which is essential to the structural and functional integrity of the small heat-shock protein alphaA-crystallin. This positively charged residue, when mutated in other small heat-shock proteins, results in various human disorders. Coimmunoprecipitation experiments showed greater binding of both HSPB8 mutants to the interacting partner HSPB1. Expression of mutant HSPB8 in cultured cells promoted formation of intracellular aggregates. Our findings provide further evidence that mutations in heat-shock proteins have an important role in neurodegenerative disorders.
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Enfermedad de Charcot-Marie-Tooth/genética , Proteínas de Choque Térmico/genética , Mutación Puntual , Proteínas Serina-Treonina Quinasas , Secuencia de Aminoácidos , Animales , Células COS , Línea Celular , Enfermedad de Charcot-Marie-Tooth/metabolismo , Femenino , Proteínas de Choque Térmico/química , Proteínas de Choque Térmico/metabolismo , Humanos , Masculino , Chaperonas Moleculares , Datos de Secuencia Molecular , Linaje , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Homología de Secuencia de Aminoácido , TransfecciónRESUMEN
Charcot-Marie-Tooth disease (CMT) is the major form of inherited peripheral neuropathy in humans. CMT is clinically and genetically heterogeneous and four aminoacyl-tRNA synthetases have been implicated in disease etiology. Mutations in the YARS gene encoding a tyrosyl-tRNA synthetase (TyrRS) lead to Dominant Intermediate CMT type C (DI-CMTC). Three dominant YARS mutations were so far associated with DI-CMTC. To further expand the spectrum of CMT causing genetic defects in this tRNA synthetase, we performed DNA sequencing of YARS coding regions in a cohort of 181 patients with various types of peripheral neuropathy. We identified a novel K265N substitution that in contrast to all previously described mutations is located at the anticodon recognition domain of the enzyme. Further genetic analysis revealed that this variant represents a benign substitution. Using our recently developed DI-CMTC Drosophila model, we tested in vivo the pathogenicity of this new YARS variant. We demonstrated that the developmental and behavioral defects induced by all DI-CMTC causing mutations were not present upon ubiquitous or panneuronal TyrRS K265N expression. Thus, in line with our genetic studies, functional analysis confirmed that the K265N substitution does not induce toxicity signs in Drosophila. The consistency observed throughout this work underscores the robustness of our DI-CMTC animal model and identifies Drosophila as a valid read-out platform to ascertain the pathogenicity of novel mutations to be identified in the future.
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Enfermedad de Charcot-Marie-Tooth/enzimología , Enfermedad de Charcot-Marie-Tooth/genética , Drosophila/genética , Mutación , Tirosina-ARNt Ligasa/genética , Animales , Animales Modificados Genéticamente , Modelos Animales de Enfermedad , Drosophila/enzimología , Expresión Génica , Vectores Genéticos , Humanos , Desempeño Psicomotor/fisiología , Análisis de Secuencia de ADNRESUMEN
Early onset hereditary motor and sensory neuropathies are rare disorders encompassing congenital hypomyelinating neuropathy with disease onset in the direct post-natal period and Dejerine-Sottas neuropathy starting in infancy. The clinical spectrum, however, reaches beyond the boundaries of these two historically defined disease entities. De novo dominant mutations in PMP22, MPZ and EGR2 are known to be a typical cause of very early onset hereditary neuropathies. In addition, mutations in several other dominant and recessive genes for Charcot-Marie-Tooth disease may lead to similar phenotypes. To estimate mutation frequencies and to gain detailed insights into the genetic and phenotypic heterogeneity of early onset hereditary neuropathies, we selected a heterogeneous cohort of 77 unrelated patients who presented with symptoms of peripheral neuropathy within the first year of life. The majority of these patients were isolated in their family. We performed systematic mutation screening by means of direct sequencing of the coding regions of 11 genes: MFN2, PMP22, MPZ, EGR2, GDAP1, NEFL, FGD4, MTMR2, PRX, SBF2 and SH3TC2. In addition, screening for the Charcot-Marie-Tooth type 1A duplication on chromosome 17p11.2-12 was performed. In 35 patients (45%), mutations were identified. Mutations in MPZ, PMP22 and EGR2 were found most frequently in patients presenting with early hypotonia and breathing difficulties. The recessive genes FGD4, PRX, MTMR2, SBF2, SH3TC2 and GDAP1 were mutated in patients presenting with early foot deformities and variable delay in motor milestones after an uneventful neonatal period. Several patients displaying congenital foot deformities but an otherwise normal early development carried the Charcot-Marie-Tooth type 1A duplication. This study clearly illustrates the genetic heterogeneity underlying hereditary neuropathies with infantile onset.
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Edad de Inicio , Neuropatía Hereditaria Motora y Sensorial/genética , Adolescente , Adulto , Anciano , Enfermedad de Charcot-Marie-Tooth/genética , Enfermedad de Charcot-Marie-Tooth/patología , Enfermedad de Charcot-Marie-Tooth/fisiopatología , Niño , Preescolar , Estudios de Cohortes , Análisis Mutacional de ADN , Neuropatía Hereditaria Motora y Sensorial/patología , Neuropatía Hereditaria Motora y Sensorial/fisiopatología , Humanos , Lactante , Persona de Mediana Edad , Mutación , Fenotipo , Adulto JovenRESUMEN
BACKGROUND: Recessive loss-of-function variations in HINT1 cause a peculiar subtype of Charcot-Marie-Tooth disease: neuromyotonia and axonal neuropathy (NMAN; OMIM[#137200]). With 25 causal variants identified worldwide, HINT1 mutations are among the most common causes of recessive neuropathy. The majority of patients are compound heterozygous or homozygous for a Slavic founder variant (c.110G>C, p.Arg37Pro) that has spread throughout Eurasia and America. RESULTS: In a cohort of 46 genetically unresolved Lithuanian patients with suspected inherited neuropathy, we identified eight families with HINT1 biallelic variations. Most patients displayed sensorimotor or motor-predominant axonal polyneuropathy and were homozygous for the p.Arg37Pro variant. However, in three families we identified a novel variant (c.299A>G, p.Glu100Gly). The same variant was also found in an American patient with distal hereditary motor neuropathy in compound heterozygous state (p.Arg37Pro/p.Glu100Gly). Haplotype analysis demonstrated a shared chromosomal region of 1.9 Mb between all p.Glu100Gly carriers, suggesting a founder effect. Functional characterization showed that the p.Glu100Gly variant renders a catalytically active enzyme, yet highly unstable in patient cells, thus supporting a loss-of-function mechanism. CONCLUSION: Our findings broaden NMAN's genetic epidemiology and have implications for the molecular diagnostics of inherited neuropathies in the Baltic region and beyond. Moreover, we provide mechanistic insights allowing patient stratification for future treatment strategies.
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Enfermedad de Charcot-Marie-Tooth , Síndrome de Isaacs , Enfermedad de Charcot-Marie-Tooth/genética , Heterocigoto , Humanos , Síndrome de Isaacs/genética , Lituania/epidemiología , Mutación/genética , Proteínas del Tejido Nervioso/genéticaRESUMEN
Hereditary spastic paraplegia (HSP) is among the most genetically diverse of all monogenic diseases. The aim was to analyze the genetic causes of HSP among adult Serbian patients. The study comprised 74 patients from 65 families clinically diagnosed with HSP during a nine-year prospective period. A panel of thirteen genes was analyzed: L1CAM (SPG1), PLP1 (SPG2), ATL1 (SPG3A), SPAST (SPG4), CYP7B1 (SPG5A), SPG7 (SPG7), KIF5A (SPG10), SPG11 (SPG11), ZYFVE26 (SPG15), REEP1 (SPG31), ATP13A2 (SPG78), DYNC1H1, and BICD2 using a next generation sequencing-based technique. A copy number variation (CNV) test for SPAST, SPG7, and SPG11 was also performed. Twenty-three patients from 19 families (29.2%) had conclusive genetic findings, including 75.0% of families with autosomal dominant and 25.0% with autosomal recessive inheritance, and 15.7% of sporadic cases. Twelve families had mutations in the SPAST gene, usually with a pure HSP phenotype. Three sporadic patients had conclusive findings in the SPG11 gene. Two unrelated patients carried a homozygous pathogenic mutation c.233T>A (p.L78*) in SPG7 that is a founder Roma mutation. One patient had a heterozygous de novo variant in the KIF5A gene, and one had a compound heterozygous mutation in the ZYFVE26 gene. The combined genetic yield of our gene panel and CNV analysis for HSP was around 30%. Our findings broaden the knowledge on the genetic epidemiology of HSP, with implications for molecular diagnostics in this region.
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Molécula L1 de Adhesión de Célula Nerviosa , Paraplejía Espástica Hereditaria , Variaciones en el Número de Copia de ADN/genética , Heterogeneidad Genética , Humanos , Cinesinas/genética , Proteínas de Transporte de Membrana/genética , Molécula L1 de Adhesión de Célula Nerviosa/genética , Fenotipo , Estudios Prospectivos , Proteínas , Serbia , Paraplejía Espástica Hereditaria/genética , Espastina/genéticaRESUMEN
BACKGROUND: Autosomal recessive axonal neuropathy with neuromyotonia has been linked to loss of functional HINT1. The disease is particularly prevalent in Central and South-East Europe, Turkey and Russia due to the high carrier frequency of the c.110G > C (p.Arg37Pro) founder variant. RESULTS: In a cohort of 748 Norwegian patients with suspected peripheral neuropathy, we identified two seemingly unrelated individuals, compound heterozygous for a new variant (c.284G > A, p.Arg95Gln) and the most common pathogenic founder variant (c.110G > C, p.Arg37Pro) in the HINT1 gene. Probands presented with motor greater than sensory neuropathy of various onset, accompanied by muscle stiffness and cramps in the limbs. Furthermore, they displayed non-classical symptoms, including pain in the extremities and signs of central nervous system involvement. Haplotype analysis in both patients revealed a common chromosomal background for p.Arg95Gln; moreover, the variant was identified in Swedish carriers. Functional characterization in HINT1-knockout and patient-derived cellular models, and in HNT1-knockout yeast, suggested that the new variant is deleterious for the function of HINT1 and provided mechanistic insights allowing patient stratification for future treatment strategies. CONCLUSION: Our findings broaden the genetic epidemiology of HINT1-neuropathy and have implications for molecular diagnostics of inherited peripheral neuropathies in Scandinavia.
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Enfermedad de Charcot-Marie-Tooth , Proteínas del Tejido Nervioso , Enfermedades del Sistema Nervioso Periférico , Europa (Continente) , Humanos , Mutación , Proteínas del Tejido Nervioso/genética , Noruega/epidemiología , Enfermedades del Sistema Nervioso Periférico/epidemiología , Enfermedades del Sistema Nervioso Periférico/genética , TurquíaRESUMEN
BACKGROUND: Recessive loss-of-function mutations in HINT1 are associated with predominantly motor axonal peripheral neuropathy with neuromyotonia. Twenty-four distinct pathogenic variants are reported all over the world, including four confirmed founder variations in Europe and Asia. The majority of patients carry the ancient Slavic founder variant c.110G>C (p.Arg37Pro) that shows a distribution gradient from east to west throughout Europe. METHODS: We report a case of HINT1 neuropathy in South America, identified by massive parallel sequencing of a neuropathy gene panel. To investigate the origin of the variant, we performed haplotyping analysis. RESULTS: A Brazilian adolescent presented with recessive axonal motor neuropathy with asymmetric onset and fasciculations. Neuromyotonia was found on needle electromyography. His parents were not consanguineous and had no European ancestry. The patient carried biallelic pathogenic p.Arg37Pro alterations in the first exon of HINT1. Both alleles were identical by descent and originated from the same ancestral founder allele as reported in Europe. CONCLUSION: Our findings expand the geographic distribution of HINT1 neuropathy to South America, where we describe a recognized founder variant in a Brazilian adolescent with no apparent European ancestry. We confirm the association of the hallmark sign of neuromyotonia with the disease.
Asunto(s)
Efecto Fundador , Síndrome de Isaacs/diagnóstico , Síndrome de Isaacs/genética , Mutación , Proteínas del Tejido Nervioso/genética , Enfermedades del Sistema Nervioso Periférico/diagnóstico , Enfermedades del Sistema Nervioso Periférico/genética , Adolescente , Alelos , Sustitución de Aminoácidos , Brasil , Femenino , Estudios de Asociación Genética , Predisposición Genética a la Enfermedad , Genotipo , Haplotipos , Humanos , América del SurRESUMEN
Hereditary sensory and autonomic neuropathies (HSAN) are clinically and genetically heterogeneous disorders characterized by axonal atrophy and degeneration, exclusively or predominantly affecting the sensory and autonomic neurons. So far, disease-associated mutations have been identified in seven genes: two genes for autosomal dominant (SPTLC1 and RAB7) and five genes for autosomal recessive forms of HSAN (WNK1/HSN2, NTRK1, NGFB, CCT5 and IKBKAP). We performed a systematic mutation screening of the coding sequences of six of these genes on a cohort of 100 familial and isolated patients diagnosed with HSAN. In addition, we screened the functional candidate gene NGFR (p75/NTR) encoding the nerve growth factor receptor. We identified disease-causing mutations in SPTLC1, RAB7, WNK1/HSN2 and NTRK1 in 19 patients, of which three mutations have not previously been reported. The phenotypes associated with mutations in NTRK1 and WNK1/HSN2 typically consisted of congenital insensitivity to pain and anhidrosis, and early-onset ulcero-mutilating sensory neuropathy, respectively. RAB7 mutations were only found in patients with a Charcot-Marie-Tooth type 2B (CMT2B) phenotype, an axonal sensory-motor neuropathy with pronounced ulcero-mutilations. In SPTLC1, we detected a novel mutation (S331F) corresponding to a previously unknown severe and early-onset HSAN phenotype. No mutations were found in NGFB, CCT5 and NGFR. Overall disease-associated mutations were found in 19% of the studied patient group, suggesting that additional genes are associated with HSAN. Our genotype-phenotype correlation study broadens the spectrum of HSAN and provides additional insights for molecular and clinical diagnosis.