Rumiko Izumi

Exome sequencing identifies a novel TTN mutation in a family with hereditary myopathy with early respiratory failure

Myofibrillar myopathy (MFM) is a group of chronic muscular disorders that show the focal dissolution of myofibrils and accumulation of degradation products. The major genetic basis of MFMs is unknown. In 1993, our group reported a Japanese family with dominantly inherited cytoplasmic body myopathy, which is now included in MFM, characterized by late-onset chronic progressive distal muscle weakness and early respiratory failure. In this study, we performed linkage analysis and exome sequencing on these patients and identified a novel c.90263G>T mutation in the TTN gene (NM_001256850). During the course of our study, another groups reported three mutations in TTN in patients with hereditary myopathy with early respiratory failure (HMERF, MIM #603689), which is characterized by overlapping pathologic findings with MFMs. Our patients were clinically compatible with HMERF. The mutation identified in this study and the three mutations in patients with HMERF were located on the A-band domain of titin, suggesting a strong relationship between mutations in the A-band domain of titin and HMERF. Mutation screening of TTN has been rarely carried out because of its huge size, consisting of 363 exons. It is possible that focused analysis of TTN may detect more mutations in patients with MFMs, especially in those with early respiratory failure.

A novel mutation in PNPLA2 causes neutral lipid storage disease with myopathy and triglyceride deposit cardiomyovasculopathy: A case report and literature review

Mutations in PNPLA2 cause neutral lipid storage disease with myopathy (NLSDM) or triglyceride deposit cardiomyovasculopathy (TGCV). We report a 59-year-old patient with NLSDM/TGCV presenting marked asymmetric skeletal myopathy and cardiomyovasculopathy. Skeletal muscle and endomyocardial biopsies showed cytoplasmic vacuoles containing neutral lipid. Gene analysis revealed a novel homozygous mutation (c.576delC) in PNPLA2. We reviewed 37 genetically-proven NLSDM/TGCV cases; median age was 30 years; distribution of myopathy was proximal (69%) and distal predominant (16%); asymmetric myopathy (right>left) was reported in 41% of the patients. Frequently-affected muscles were posterior compartment of leg (75%), shoulder girdle to upper arm (50%), and paraspinal (33%). Skeletal muscle biopsies showed lipid accumulation in 100% and rimmed vacuoles in 22%. Frequent comorbidities were cardiomyopathy (44%), hyperlipidemia (23%), diabetes mellitus (24%), and pancreatitis (14%). PNPLA2 mutations concentrated in Exon 4-7 without apparent genotype-phenotype correlations. To know the characteristic features is essential for the early diagnosis of NLSDM/TGCV.

GNE myopathy associated with congenital thrombocytopenia: A report of two siblings

GNE myopathy is an autosomal recessive muscular disorder caused by mutations in the gene encoding the key enzyme in sialic acid biosynthesis, UDP-N-acetylglucosamine 2-epimerase/N-acetylmannosamine kinase (GNE/MNK). Here, we report two siblings with myopathy with rimmed vacuoles and congenital thrombocytopenia who harbored two compound heterozygous GNE mutations, p.V603L and p.G739S. Thrombocytopenia, which is characterized by shortened platelet lifetime rather than ineffective thrombopoiesis, has been observed since infancy. We performed exome sequencing and array CGH to identify the underlying genetic etiology of thrombocytopenia. No pathogenic variants were detected among the known causative genes of recessively inherited thrombocytopenia; yet, candidate variants in two genes that followed an autosomal recessive mode of inheritance, including previously identified GNE mutations, were detected. Alternatively, it is possible that the decreased activity of GNE/MNK itself, which would lead to decreased sialic content in platelets, is associated with thrombocytopenia in these patients. Further investigations are required to clarify the association between GNE myopathy and the pathogenesis of thrombocytopenia.

Proteasome dysfunction induces muscle growth defects and protein aggregation.

ABSTRACT The ubiquitin–proteasome and autophagy–lysosome pathways are the two major routes of protein and organelle clearance. The role of the proteasome pathway in mammalian muscle has not been examined in vivo. In this study, we report that the muscle-specific deletion of a crucial proteasomal gene, Rpt3 (also known as Psmc4), resulted in profound muscle growth defects and a decrease in force production in mice. Specifically, developing muscles in conditional Rpt3-knockout animals showed dysregulated proteasomal activity. The autophagy pathway was upregulated, but the process of autophagosome formation was impaired. A microscopic analysis revealed the accumulation of basophilic inclusions and disorganization of the sarcomeres in young adult mice. Our results suggest that appropriate proteasomal activity is important for muscle growth and for maintaining myofiber integrity in collaboration with autophagy pathways. The deletion of a component of the proteasome complex contributed to myofiber degeneration and weakness in muscle disorders that are characterized by the accumulation of abnormal inclusions.

Comprehensive targeted next-generation sequencing in Japanese familial amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult-onset neurodegenerative disease characterized by loss of motor neurons. We have recently identified SOD1 and FUS mutations as the most common causes in a consecutive series of 111 familial ALS pedigrees in Japan. To reveal possible genetic causes for the remaining 51 patients with familial ALS (45 pedigrees), we performed targeted next-generation sequencing of 35 known ALS/motor neuron diseases-related genes. Known variants in ANG, OPTN, SETX, and TARDBP were identified in 6 patients. A novel likely pathogenic homozygous variant in ALS2 was identified in 1 patient. In addition, 18 patients harbored 1-3 novel variants of uncertain significance, whereas hexanucleotide repeat expansions in C9ORF72 were not detected using repeat-primed polymerase chain reaction. Collectively, in our Japanese cohort, the frequencies of SOD1, FUS, SETX, TARDBP, ANG, and OPTN variants were 32%, 11%, 2%, 2%, 1%, and 1%, respectively. These findings indicate considerable differences in the genetic variations associated with familial ALS across populations. Further genetic analyses and functional studies of novel variants are warranted.

Genetic profile for suspected dysferlinopathy identified by targeted next-generation sequencing

Objective: To investigate the genetic causes of suspected dysferlinopathy and to reveal the genetic profile for myopathies with dysferlin deficiency. Methods: Using next-generation sequencing, we analyzed 42 myopathy-associated genes, including DYSF, in 64 patients who were clinically or pathologically suspected of having dysferlinopathy. Putative pathogenic mutations were confirmed by Sanger sequencing. In addition, copy-number variations in DYSF were investigated using multiplex ligation-dependent probe amplification. We also analyzed the genetic profile for 90 patients with myopathy with dysferlin deficiency, as indicated by muscle specimen immunohistochemistry, including patients from a previous cohort. Results: We identified putative pathogenic mutations in 38 patients (59% of all investigated patients). Twenty-three patients had DYSF mutations, including 6 novel mutations. The remaining 16 patients, including a single patient who also carried the DYSF mutation, harbored putative pathogenic mutations in other genes. The genetic profile for 90 patients with dysferlin deficiency revealed that 70% had DYSF mutations (n = 63), 10% had CAPN3 mutations (n = 9), 2% had CAV3 mutations (n = 2), 3% had mutations in other genes (in single patients), and 16% did not have any identified mutations (n = 14). Conclusions: This study clarified the heterogeneous genetic profile for myopathies with dysferlin deficiency. Our results demonstrate the importance of a comprehensive analysis of related genes in improving the genetic diagnosis of dysferlinopathy as one of the most common subtypes of limb-girdle muscular dystrophy. Unresolved diagnoses should be investigated using whole-genome or whole-exome sequencing.

Isolated inclusion body myopathy caused by a multisystem proteinopathy–linked hnRNPA1 mutation

Objective: To identify the genetic cause of isolated inclusion body myopathy (IBM) with autosomal dominant inheritance in 2 families. Methods: Genetic investigations were performed using whole-exome and Sanger sequencing of the heterogeneous nuclear ribonucleoprotein A1 gene (hnRNPA1). The clinical and pathologic features of patients in the 2 families were evaluated with neurologic examinations, muscle imaging, and muscle biopsy. Results: We identified a missense p.D314N mutation in hnRNPA1, which is also known to cause familial amyotrophic lateral sclerosis, in 2 families with IBM. The affected individuals developed muscle weakness in their 40s, which slowly progressed toward a limb-girdle pattern. Further evaluation of the affected individuals revealed no apparent motor neuron dysfunction, cognitive impairment, or bone abnormality. The muscle pathology was compatible with IBM, lacking apparent neurogenic change and inflammation. Multiple immunohistochemical analyses revealed the cytoplasmic aggregation of hnRNPA1 in close association with autophagosomes and myonuclei. Furthermore, the aberrant accumulation was characterized by coaggregation with ubiquitin, sequestome-1/p62, valosin-containing protein/p97, and a variety of RNA-binding proteins (RBPs). Conclusions: The present study expands the clinical phenotype of hnRNPA1-linked multisystem proteinopathy. Mutations in hnRNPA1, and possibly hnRNPA2B1, will be responsible for isolated IBM with a pure muscular phenotype. Although the mechanisms underlying the selective skeletal muscle involvement remain to be elucidated, the immunohistochemical results suggest a broad sequestration of RBPs by the mutated hnRNPA1.

Aberrant astrocytic expression of chondroitin sulfate proteoglycan receptors in a rat model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease. Progressive and systemic loss of motor neurons with gliosis in the central nervous system (CNS) is a neuropathological hallmark of ALS. Chondroitin sulfate proteoglycans (CSPGs) are the major components of the extracellular matrix of the mammalian CNS, and they inhibit axonal regeneration physically by participating to form the glial scar. Recently, protein tyrosine phosphatase sigma (PTPσ) and leukocyte common antigen‐related protein were discovered as CSPG receptors that play roles in inhibiting regeneration. Here we examined the expression of CSPG receptors in transgenic female rats overexpressing an ALS‐linked mutant cytosolic Cu/Zn superoxide dismutase gene (SOD1). In contrast to controls, multiple immunofluorescence analyses revealed aberrant expression of CSPG receptors dominantly in reactive astrocytes, while PTPσ expression in neurons decreased in the spinal ventral horns of ALS transgenic rats. The aberrant and progressive astrocytic expression of CSPG receptors and reactive astrocytes themselves may be therapeutic targets for reconstructing a regeneration‐supportive microenvironment under neurodegenerative conditions such as ALS.

Genotype-phenotype relationships in familial amyotrophic lateral sclerosis with FUS/TLS mutations in Japan.

Introduction: We investigated possible genotype–phenotype correlations in Japanese patients with familial amyotrophic lateral sclerosis (FALS) carrying fused in sarcoma/translated in liposarcoma (FUS/TLS) gene mutations. Methods: A consecutive series of 111 Japanese FALS pedigrees were screened for copper/zinc superoxide dismutase 1 (SOD1) and FUS/TLS gene mutations. Clinical data, including onset age, onset site, disease duration, and extramotor symptoms, were collected. Results: Nine different FUS/TLS mutations were found in 12 pedigrees. Most of the patients with FUS/TLS‐linked FALS demonstrated early onset in the brainstem/upper cervical region, and relatively short disease duration. A few mutations exhibited phenotypes that were distinct from typical cases. Frontotemporal dementia was present in 1 patient. Conclusions: This study revealed a characteristic phenotype in FUS/TLS‐linked FALS patients in Japan. FUS/TLS screening is recommended in patients with FALS with this phenotype. Muscle Nerve 54: 398–404, 2016

Focal Segmental Glomerulosclerosis Associated with Chronic Progressive External Ophthalmoplegia and Mitochondrial DNA A3243G Mutation

Focal segmental glomerulosclerosis (FSGS) is caused by various etiologies, with mitochondrial dysfunction being one of the causes. FSGS is known to be associated with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS), which is a subclass of mitochondrial disease. However, it has rarely been reported in other mitochondrial disease subclasses. Here, we reported a 20-year-old man diagnosed with FSGS associated with chronic progressive external ophthalmoplegia (CPEO) due to mitochondrial DNA (mtDNA) 3243A>G mutation. He presented with left ptosis, short stature, mild sensorineural deafness, and cardiac conduction block. A renal biopsy sample showed segmental sclerosis and adhesions between capillaries and Bowman’s capsule, indicating FSGS. Electron microscopy demonstrated abnormal aggregated mitochondria in podocytes, and the basement membrane and epithelial cells of Bowman’s capsule. Skeletal muscle biopsy also showed accumulation of abnormal mitochondria. mtDNA analysis identified heteroplasmic mtDNA 3243A>G mutation with no large-scale deletions. From these findings, we diagnosed the case as CPEO with multi-organ involvement including FSGS. Our report demonstrates that CPEO, as well as MELAS, can be associated with FSGS. Because mitochondrial disease presents with a variety of clinical symptoms, atypical cases with non-classical manifestations are observed. Thus, mitochondrial disease should be considered as an underlying cause of FSGS with systemic manifestations even with atypical phenotypes.