Spinocerebellar ataxia with axonal neuropathy: consequence of a Tdp1 recessive neomorphic mutation?

Tyrosyl-DNA phosphodiesterase 1 (Tdp1) cleaves the phosphodiester bond between a covalently stalled topoisomerase I (Topo I) and the 3' end of DNA. Stalling of Topo I at DNA strand breaks is induced by endogenous DNA damage and the Topo I-specific anticancer drug camptothecin (CPT). The H493R mutation of Tdp1 causes the neurodegenerative disorder spinocerebellar ataxia with axonal neuropathy (SCAN1). Contrary to the hypothesis that SCAN1 arises from catalytically inactive Tdp1, Tdp1-/- mice are indistinguishable from wild-type mice, physically, histologically, behaviorally, and electrophysiologically. However, compared to wild-type mice, Tdp1-/- mice are hypersensitive to CPT and bleomycin but not to etoposide. Consistent with earlier in vitro studies, we show that the H493R Tdp1 mutant protein retains residual activity and becomes covalently trapped on the DNA after CPT treatment of SCAN1 cells. This result provides a direct demonstration that Tdp1 repairs Topo I covalent lesions in vivo and suggests that SCAN1 arises from the recessive neomorphic mutation H493R. This is a novel mechanism for disease since neomorphic mutations are generally dominant.

Spinocerebellar ataxia with axonal neuropathy.

Spinocerebellar ataxia with axonal neuropathy (SCAN 1) is an autosomal recessive disorder caused by a specific point mutation (c.1478A>G, p.H493R) in the tyrosyl-DNA phosphodiesterase (TDP1) gene. Functional and genetic studies suggest that this mutation, which disrupts the active site of the Tdp1 enzyme, causes disease by a combination of decreased catalytic activity and stabilization of the normally transient covalent Tdp1-DNA intermediate. This covalent reaction intermediate can form during the repair of stalled topoisomerase I-DNA adducts or oxidatively damaged bases at the 3' end of the DNA at a strand break. However, our current understanding of the biology of Tdp1 function in humans is limited and does not allow us to fully elucidate the disease mechanism.

Clinical and genetic characterization of 16q-linked autosomal dominant spinocerebellar ataxia in South Kyushu, Japan.

16q-ADCA (OMIM no. 117210) is an autosomal dominant spinocerebellar ataxia (AD-SCA) characterized by late-onset pure cerebellar ataxia and -16C>T substitution of the puratrophin-1 gene. Recently, a series of single-nucleotide polymorphisms (haplotype block) were found to be specific to 16q-ADCA. We screened patients with ataxia and found 62 patients, including four homozygotes who carry the C-T substitution of the puratrophin-1 gene. By further analysis of the patients with the haplotype block, we observed a single-founder effect for 16q-ADCA, even in patients who are supposed to be sporadic late cortical cerebellar atrophy (LCCA). We also observed slippage mutations of microsatellite markers, GATA01 and 17 msm, in the pedigrees. We compared the clinical course of 16q-ADCA in heterozygotes and homozygotes with the haplotype block and observed no apparent gene dosage effect. 16q-ADCA accounts for 27% of AD-SCAs and is the most frequent AD-SCA in South Kyushu, Japan.

Neurologic phenotype of Schimke immuno-osseous dysplasia and neurodevelopmental expression of SMARCAL1.

Schimke immuno-osseous dysplasia (OMIM 242900) is an uncommon autosomal-recessive multisystem disease caused by mutations in SMARCAL1 (swi/snf-related, matrix-associated, actin-dependent regulator of chromatin, subfamily a-like 1), a gene encoding a putative chromatin remodeling protein. Neurologic manifestations identified to date relate to enhanced atherosclerosis and cerebrovascular disease. Based on a clinical survey, we determined that half of Schimke immuno-osseous dysplasia patients have a small head circumference, and 15% have social, language, motor, or cognitive abnormalities. Postmortem examination of 2 Schimke immuno-osseous dysplasia patients showed low brain weights and subtle brain histologic abnormalities suggestive of perturbed neuron-glial migration such as heterotopia, irregular cortical thickness, incomplete gyral formation, and poor definition of cortical layers. We found that SMARCAL1 is highly expressed in the developing and adult mouse and human brain, including neural precursors and neuronal lineage cells. These observations suggest that SMARCAL1 deficiency may influence brain development and function in addition to its previously recognized effect on cerebral circulation.

Reduced Foxp3 expression with increased cytomegalovirus-specific CTL in HTLV-I-associated myelopathy.

Human T-lymphotropic virus type I (HTLV-I)-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients show high immune responses to HTLV-I. However, it is unclear whether the cytotoxic T lymphocyte (CTL) responses to other chronic viruses also increase. We investigated the responses in the peripheral blood by using HLA-A*0201/peptide pentamers. The frequency of cytomegalovirus (CMV)-specific CTL tended to be higher in HAM/TSP patients than in healthy controls (HCs). The frequency of CMV-specific CTL positively correlated with that of HTLV-I Tax-specific CTL. The frequency of Foxp3+ cells in CD4+ lymphocytes tended to be higher in HAM/TSP patients than in ACs and HCs. The expression level of Foxp3 was lower in HAM/TSP patients than in HCs and was inversely correlated with the CMV-specific CTL frequency. A percentage of Foxp3+ cells showed a positive correlation with the HTLV-I proviral load. These results suggest that a decrease in the Foxp3 expression may contribute to the high immune response to CMV and that the Foxp3+ regulatory T cells may play a role in the immune surveillance of HTLV-I.

New type of encephalomyelitis responsive to trimethoprim/sulfamethoxazole treatment in Japan.

OBJECTIVE: To determine the causative pathogen and investigate the effective treatment of a new type of encephalomyelitis with an unknown pathogen in Japan and report the preliminary ultrastructural and genomic characterization of the causative agent. METHODS: From 2005 to 2012, we treated 4 Japanese patients with geographic clustering and comparable clinical features, serum/CSF cytology, and radiologic findings. Brain biopsy was conducted in all patients to analyze neuropathologic changes by histology, and electron microscopy was applied to reveal the features of the putative pathogen. Genomic DNA was obtained from the affected brain tissues and CSF, and an unbiased high-throughput sequencing approach was used to screen for specific genomic sequences indicative of the pathogen origin. RESULTS: All patients exhibited progressive dementia with involuntary tongue movements. Cytologic examination of CSF revealed elevated mononuclear cells. Abnormal MRI signals were observed in temporal lobes, subcortical white matter, and spinal cord. Biopsied brain tissue exhibited aggregated periodic acid-Schiff-positive macrophages and 2-7 µm diameter round/oval bodies without nuclei or cell walls scattered around the vessels. Unbiased high-throughput sequencing identified more than 100 archaea-specific DNA fragments. All patients were responsive to trimethoprim/sulfamethoxazole (TMP-SMX) plus corticosteroid therapy. CONCLUSIONS: We report 4 cases of encephalomyelitis due to an unknown pathogen. On the basis of ultrastructural and genomic studies, we propose a new disease entity resulting from a causative pathogen having archaeal features. TMP-SMX therapy was effective against this new type of encephalomyelitis.

Pyogenic liver abscess related to dental disease in an immunocompetent host.

A 59-year-old man with poor oral hygiene presented to our hospital because of fever and chills. Abdominal ultrasonography and enhanced computed tomography (CT) revealed a liver abscess. The patient had no history of immunodeficiency and we confirmed the patient had no immunologic abnormalities. Blood culture revealed Fusobacterium nucleatum, a bacterium commonly found in the oral cavity. Even if a patient is immunocompetent, poor oral hygiene might be an independent risk factor for a pyogenic liver abscess. Professional mechanical tooth cleaning (PMTC) and appropriate self-care are recommended as a prophylaxis against not only dental, but also systemic diseases.

Suppression of discoidin domain receptor 1 by RNA interference attenuates lung inflammation.

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase whose ligand is collagen. Recently, we have reported the association of DDR1 in the cytokine production of human leukocytes in in vitro and in vivo expression in idiopathic pulmonary fibrosis. However, its role in in vivo inflammation has not been fully elucidated. Small interference RNA (siRNA) can induce specific suppression of in vitro and in vivo gene expression. In this study, using a bleomycin-induced pulmonary fibrosis mouse model, we administered siRNA against DDR1 transnasally and evaluated histological changes, cytokine expression, and signaling molecule activation in the lungs. Histologically, siRNA against DDR1 successfully reduced in vivo DDR1 expression and attenuated bleomycin-induced infiltration of inflammatory cells. Furthermore, it significantly reduced inflammatory cell counts and concentrations of cytokines such as MCP-1, MIP-1alpha, and MIP-2 in bronchoalveolar lavage fluid. Subsequently, bleomycin-induced up-regulation of TGF-beta in bronchoalveolar lavage fluid was significantly inhibited, and collagen deposition in the lungs was reduced. Furthermore, siRNA against DDR1 significantly inhibited bleomycin-induced P38 MAPK activation in the lungs. Considered together, we propose that DDR1 contributes to the development of bleomycin-induced pulmonary inflammation and fibrosis.

Molecular mechanism of rigid spine with muscular dystrophy type 1 caused by novel mutations of selenoprotein N gene.

Mutations of selenoprotein N, 1 gene (SEPN1) cause rigid spine with muscular dystrophy type 1 (RSMD1), multiminicore disease, and desmin-related myopathy. We found two novel SEPN1 mutations in two Japanese patients with RSMD1. To clarify the pathomechanism of RSMD1, we performed immunohistochemical studies using a newly developed antibody for selenoprotein N. Selenoprotein N was diffusely distributed in the cytoplasm of the control muscle, but was reduced and irregularly expressed in the cytoplasm of a patient with RSMD1. The expression pattern was very similar to that of calnexin, a transmembrane protein of the endoplasmic reticulum. Selenoprotein N seems to be an endoplasmic reticulum glycoprotein, and loss of this protein leads to disturbance of muscular function. One of the families had the SEPN1 homozygous mutation in the initiation codon 1_2 ins T in exon 1 and showed truncated protein expression. The other had a homozygous 20-base duplication mutation at 80 (80_99dup, frameshift at R27) which, in theory, should generate many nonsense mutations including TGA. These nonsense mutations are premature translation termination codons and they degrade immediately by the process of nonsense-mediated decay (NMD). However, truncated selenoprotein N was also expressed. A possible mechanism behind this observation is that SEPN1 mRNAs may be resistant to NMD. We report on the possible molecular mechanism behind these mutations in SEPN1. Our study clarifies molecular mechanisms of this muscular disorder.

Fine mapping of 16q-linked autosomal dominant cerebellar ataxia type III in Japanese families.

The autosomal dominant cerebellar ataxias (ADCAs) are a clinically and genetically heterogeneous group of disorders. To date, at least 11 genes and 13 additional loci have been identified in ADCAs. Despite phenotypic differences, spinocerebellar ataxia 4 (SCA4) and Japanese 16q-linked ADCA type III map to the same region of 16q22.1. We report four Japanese families with pure cerebellar ataxia and a disease locus at 16q22.1. Our families yielded a peak lod score of 6.01 at marker D16S3141. To refine the candidate region, we carried out genetic linkage studies in four pedigrees with a high density set of DNA markers from chromosome 16q22.1. Our linkage data suggest that the disease locus for 16q-ADCA type III is within the 1.25-Mb interval delineated by markers 17msm and CTTT01. We screened for mutations in 36 genes within the critical region. Our critical region lies within the linkage interval reported for SCA4 and for Japanese 16q-ADCA type III. These data suggest that the ADCA that we have characterized is allelic with SCA4 and Japanese 16q-linked ADCA type III.