Transglutaminase 6 Research Articles

A case report of late-onset cerebellar ataxia associated with a rare p.R342W TGM6 (SCA35) mutation

BackgroundMutations in TGM6 gene, encoding for transglutaminase 6 (TG6), have been implicated in the pathogenesis of spinocerebellar ataxia type 35 (SCA35), a rare autosomal dominant disease marked by cerebellar degeneration and characterized by postural instability, incoordination of gait, features of cerebellar dysfunction and pyramidal signs.Case presentationHere we report the case of an Italian patient with late-onset, slowly progressive cerebellar features, including gait ataxia, scanning speech and ocular dysmetria and pyramidal tract signs. Whole exome sequencing revealed the rare heterozygous c.1024C > T (p.R342W) variant of TGM6, located at a highly evolutionary conserved position and predicted as pathogenic by in silico tools. Expression of TG6-R342W mutant in HEK293T cells led to a significant reduction of transamidase activity compared to wild-type TG6.ConclusionThis finding extends SCA35 genetic landscape, highlighting the importance of TGM6 screening in undiagnosed late-onset and slowly progressive cerebellar ataxias.

Hispanic Spinocerebellar Ataxia Type 35 (SCA35) with a Novel Frameshift Mutation

Genetic mutations in transglutaminase 6 (TGM6) are recently identified to be associated with spinocerebellar ataxia type 35 (SCA35). We report a Hispanic SCA35 patient, who was confirmed to have a heterozygous, single-nucleotide deletion in TGM6, causing a frameshift mutation with a premature stop codon. An immune-mediated ataxia previously found to be associated with autoantibody reactivity to TG6 may share a similar pathomechanism to SCA35, suggesting a converging role for TG6 in cerebellar function.

The Occurrence of Antibodies Against Gluten in Children with Autism Spectrum Disorders Does Not Correlate with Serological Markers of Impaired Intestinal Permeability.

There is evidence that children with autism spectrum disorders (ASDs) display an increased immune reactivity against gluten, which is supposed to be the effect of intestinal barrier abnormalities. The aim of study was to evaluate the relation of antibody induced by gluten to zonulin and intestinal fatty acid binding proteins (I-FABP), that is, serological markers of an impaired gut barrier. The study included 77 patients with ASDs. Zonulin, I-FABP, celiac-specific antibodies, anti-gliadin antibodies (AGA), and antibodies against neural transglutaminase 6 (TG6) of immunoglobulin (Ig) A and IgG classes were detected in sera. Celiac-specific antibodies were negative in all ASD children, four children (5.2%) had positive anti-TG6 antibodies, and increased AGA-IgG production was found in 21 patients (27.3%). Mean levels of zonulin and I-FABP in ASD patients were similar to those found in healthy controls and revealed a negative correlation with age, whereas regression analysis revealed a significant positive relationship between antibody production and the age. Serum concentrations of zonulin and I-FABP showed no statistically significant association with antibody positivity. An increased production of antibodies related to gliadin and neural TG6 in ASD children is not related to serological markers of an impaired intestinal barrier.

Mutations in TGM6 induce the unfolded protein response in SCA35.

Spinocerebellar ataxia type 35 (SCA35) is a rare autosomal-dominant neurodegenerative disease caused by mutations in the TGM6 gene, which codes for transglutaminase 6 (TG6). Mutations in TG6 induce cerebellar degeneration by an unknown mechanism. We identified seven patients bearing new mutations in TGM6. To gain insights into the molecular basis of mutant TG6-induced neurotoxicity, we analyzed all the seven new TG6 mutants and the five TG6 mutants previously linked to SCA35. We found that the wild-type (TG6-WT) protein mainly localized to the nucleus and perinuclear area, whereas five TG6 mutations showed nuclear depletion, increased accumulation in the perinuclear area, insolubility and loss of enzymatic function. Aberrant accumulation of these TG6 mutants in the perinuclear area led to activation of the unfolded protein response (UPR), suggesting that specific TG6 mutants elicit an endoplasmic reticulum stress response. Mutations associated with activation of the UPR caused death of primary neurons and reduced the survival of novel Drosophila melanogaster models of SCA35. These results indicate that mutations differently impacting on TG6 function cause neuronal dysfunction and death through diverse mechanisms and highlight the UPR as a potential therapeutic target for patient treatment.

Transglutaminase-6 is an autoantigen in progressive multiple sclerosis and is upregulated in reactive astrocytes

Background: Transglutaminase-6 (TGM6), a member of the transglutaminase enzyme family, is found predominantly in central nervous system (CNS) neurons under physiological conditions. It has been proposed as an autoimmune target in cerebral palsy, gluten-sensitive cerebellar ataxia, and schizophrenia. Objective: To investigate TGM6 involvement in multiple sclerosis (MS). Methods: Antibody levels against TGM6 (TGM6-IgG) were measured in the cerebrospinal fluid (CSF) of 62 primary progressive multiple sclerosis (PPMS), 85 secondary progressive multiple sclerosis (SPMS), and 50 relapsing-remitting multiple sclerosis (RRMS) patients and 51 controls. TGM6 protein expression was analyzed in MS brain autopsy, murine experimental autoimmune encephalomyelitis (EAE), and cultured astrocytes. Results: CSF levels of TGM6-IgG were significantly higher in PPMS and SPMS compared to RRMS and controls. Notably, patients with clinically active disease had the highest TGM6-IgG levels. Additionally, brain pathology revealed strong TGM6 expression by reactive astrocytes within MS plaques. In EAE, TGM6 expression in the spinal cord correlated with disease course and localized in reactive astrocytes infiltrating white matter lesions. Finally, knocking down TGM6 expression in cultured reactive astrocytes reduced their glial fibrillary acidic protein (GFAP) expression. Conclusion: TGM6-IgG may be a candidate CSF biomarker to predict and monitor disease activity in progressive MS patients. Furthermore, TGM6 expression by reactive astrocytes within both human and mouse lesions suggests its involvement in the mechanisms of glial scar formation.

Transglutaminase 6 Antibodies in the Serum of Patients With Amyotrophic Lateral Sclerosis.

Celiac disease is an autoimmune disorder triggered by gluten in genetically predisposed individuals. Gluten sensitivity can cause neurologic manifestations, such as ataxia or neuropathy, with or without gastrointestinal symptoms. Many patients with gluten ataxia produce antibodies toward the newly identified neuronal transglutaminase 6 (TG6). Two case reports described patients initially diagnosed with amyotrophic lateral sclerosis (ALS) and ultimately with celiac disease who improved with a strict gluten-free diet. To evaluate the prevalence of celiac disease-related antibodies and HLA antigen alleles, as well as TG6 antibodies, in patients with ALS and healthy individuals serving as controls to determine whether a neurologic presentation of a gluten-related disorder mimicking ALS might occur in some patients. In a case-control study conducted in an ALS tertiary center, we measured serum levels of total IgA antibodies, IgA antibodies to transglutaminase 2 (TG2) and endomysium, as well as IgA and IgG antibodies to deamidated gliadine peptide and TG6 and performed HLA antigen genotyping in 150 consecutive patients with ALS and 115 healthy volunteers of similar age and sex. Participants did not have any known autoimmune or gastroenterologic disorder and were not receiving any immunomodulatory medications. The study was conducted from July 1, 2010, to December 31, 2012. Antibody levels and frequency of individuals with abnormal antibody values as well as frequency of HLA antigen alleles were compared between patient and control groups. All patients and control group participants were seronegative to IgA antibodies to TG2, endomysium, and deamidated gliadine peptide. Twenty-three patients (15.3%) were seropositive to TG6 IgA antibodies as opposed to only 5 controls (4.3%) (P = .004). The patients seropositive for TG6 showed a classic picture of ALS, similar to that of seronegative patients. Fifty patients and 20 controls were tested for celiac disease-specific HLA antigen alleles; 13 of 22 TG6 IgA seropositive individuals (59.1%) were seropositive for celiac disease-related alleles compared with 8 (28.6%) of the 28 seronegative individuals (P = .04). Mean (SD) levels of IgA antibodies to TG2 were 1.78 (0.73) in patients and 1.58 (0.68) in controls (normal, <10). In a subset of study participants, mean levels of deamidated gliadin peptide autoantibodies were 7.46 (6.92) in patients and 6.08 (3.90) in controls (normal, <16). Mean levels of IgA antibodies to TG6 were 29.3 (30.1) in patients and 21.0 (27.4) in controls (P = .02; normal, <26). The data from this study indicate that, in certain cases, an ALS syndrome might be associated with autoimmunity and gluten sensitivity. Although the data are preliminary and need replication, gluten sensitivity is potentially treatable; therefore, this diagnostic challenge should not be overlooked.

Spinocerebellar ataxia 35: novel mutations in TGM6 with clinical and genetic characterization.

To elucidate the clinical and cellular characteristics of spinocerebellar ataxia type 35 (SCA35), which is caused by mutations in the TGM6 gene encoding transglutaminase 6 (TG6), in a Taiwanese cohort. Mutations in TGM6 were ascertained in 109 unrelated probands of Chinese descent with molecularly unassigned SCA from 512 pedigrees, in whom mutations responsible for 15 other ataxia syndromes had been excluded. The clinical features of all patients with a TGM6 mutation were systematically analyzed. The biological consequences of the newly identified TGM6 mutations were investigated in HEK293 cells transfected with mutant complementary DNA constructs. Two missense mutations (p.R111C and p.D510H) and one 3-base pair deletion (p.E574del) in TGM6 were identified. Among them, p.R111C and p.E574del were novel. The common features of SCA35 include a slowly progressive clinical course, trunk/limb ataxia, and hand tremors. The age at onset varies from adolescence to the fifth decade. Torticollis and intellectual impairment are rare manifestations. Brain MRI reveals diffuse cerebellar atrophy without involvement of the cerebral hemispheres or brainstem. The 3 mutations identified here attenuated the protein stability and catalytic activities of TG6. SCA35 is an uncommon ataxia syndrome, accounting for 0.6% (3/512) of SCAs among the Han-Chinese descent in Taiwan. This study broadens the mutational spectrum of SCA35 and stresses the importance of TG6 in cerebellar functions.

Distribution of Transglutaminase 6 in the Central Nervous System of Adult Mice

Our previous study identified a new form of spinocerebellar ataxia (SCA), in which mutations in the gene coding for transglutaminase 6 (TG6) were suggested to be causative. However, the data concerning cellular distribution of TG6 in the brain is still fragmentary. Therefore, we now report a comprehensive immunohistochemical examination of the expression profile of TG6 in adult mouse brain. TG6 was abundantly expressed in the septal region, basal ganglia, hypothalamus and brainstem. Notably, numerous TG6-positive neurons were found in the key brain regions involved in regulating locomotion activity, including the globus pallidus, subthalamic nucleus, substantia nigra, cerebellum, some precerebellar nuclei, and spinal motor neurons. Double immunostaining showed that the vast majority of TG6-positive neurons in the reticular nigra were GABAergic and those in the compact nigra were not dopaminergic. In addition, double staining for TG6 with either anti-NeuN or glial fibrillary acidic protein (GFAP) antibodies demonstrated exclusive NeuN-TG6 co-localization. This study presents a comprehensive overview of TG6 expression in the mouse brain, and provides insight for investigating the role of TG6 in the development of SCA.

Spotlight on the May 7 issue

The authors assessed the influence of cognitive reserve (CR) on the evolution of cognitive performance over a 1.6-year follow-up period in 35 patients with relapsing-remitting multiple sclerosis. CR protected patients' cognitive performance in those with higher cortical volumes, pointing to a time window of intervention in the earliest phases of the disease. See p. 1728; Editorial, p. 1724 This study looked at the prevalence of transglutaminase 6 (TG6) in gluten-related diseases and controls, as well as the ability of TG6 antibody to identify patients with gluten ataxia in the absence of other gluten-related serologic markers. Antibodies against TG6 were gluten-dependent and …

Whole exome sequencing identifies a novel mutation in the transglutaminase 6 gene for spinocerebellar ataxia in a Chinese family

Autosomal dominant spinocerebellar ataxias (SCA) constitute a heterogeneous group of inherited disorders. The transglutaminase 6 (TGM6) gene was recently suggested as a SCA causative gene in Chinese SCA families. In this study, two affected members of a three-generation Chinese family with SCA characterized by progressive cerebellar ataxia and lower limb pyramidal signs were subjected to whole exome sequencing. Through bioinformatics analysis of the sequence variants in these two individuals, we identified a novel mutation in the TGM6 gene (c.1528G>C) which showed perfect co-segregation with disease phenotype in all nine members of this family. This finding confirms that mutations in TGM6 gene represent an important cause of SCA in Chinese. This study also shows that whole exome sequencing of a small number of affected individuals, leveraged on bioinformatics analysis, can be an efficient strategy for identifying causative mutations in rare Mendelian disorders.

Spinocerebellar ataxia type 35 (SCA35)-associated transglutaminase 6 mutants sensitize cells to apoptosis

Spinocerebellar ataxia type 35 (SCA35) is an autosomal dominant neurodegenerative disorder. In our previous study, using exome sequencing and linkage analysis, two missense mutations of the transglutaminase 6 (TGM6) gene were identified as causative for SCA35. TGM6 encodes transglutaminase 6 (TG6), a member of the transglutaminase family of enzymes that catalyze the formation of a covalent bond between a free amine group and the γ-carboxamide group of protein- or peptide-bound glutamine. However, the precise role of TG6 in contributing to SCA35 remains unclear. In this study, we analyzed the subcellular distribution, expression and in vitro activity of two missense mutations of TG6 (D327G, L517W) and found that both mutants exhibited decreased transglutaminase activity and stability. Furthermore, overexpressing the TG6 mutants sensitized cells to staurosporine-induced apoptosis by increasing the activity of caspases. We propose that the pro-apoptotic role of these mutants might underlie the pathogenesis of SCA35.

New Serology Assays Can Detect Gluten Sensitivity among Enteropathy Patients Seronegative for Anti–Tissue Transglutaminase

Some patients with celiac disease (CD) may be seronegative with the commonly used test for IgA anti-tissue transglutaminase (anti-tTG) antibodies. Our aim was to explore whether newer assays incorporating synthetic deamidated gliadin-related peptides (DGPs) or other TG isoenzymes as antigen are useful for detecting gluten sensitivity in IgA anti-tTG-seronegative patients. We assayed serum samples obtained at diagnosis from (a) anti-tTG-seronegative patients with a CD-like enteropathy (n = 12), (b) skin biopsy-proven dermatitis herpetiformis (DH) patients (n = 26), and (c) IgA anti-tTG-positive CD patients (n = 26). All patients had typical total IgA concentrations. All patients underwent intestinal biopsy and serum testing for (a) detection of IgA and IgG isotypes of both anti-DGP and anti-tTG in a single assay (tTG/DGP Screen; INOVA Diagnostics), (b) simultaneous detection of both IgA and IgG anti-DGP antibody isotypes (DGP Dual; INOVA Diagnostics), and (c) detection of antibodies to transglutaminase 3 (TG3) or transglutaminase 6 (TG6). All anti-tTG-seropositive patients also tested positive in anti-DGP assays. Overall, tTG/DGP Screen detected 6 (31.6%) of the 19 anti-tTG seronegatives, and anti-DGP Dual produced positive results in 5 (26.3%) of these cases. Whereas both assays detected 2 anti-tTG-negative DH patients with partial villous atrophy, they were positive in only 2 of the 5 cases with no histologically discernible mucosal damage. Testing for antibodies to TG3 and TG6 identified 7 (36.8%) of the 19 anti-tTG-negative patients, 5 of which were also positive for anti-DGP. Detection of anti-DGP with tTG/DGP Screen or anti-DGP Dual, or detection of antibodies to other TG isoenzymes, enhances the sensitivity for detecting gluten sensitivity among non-IgA- deficient, anti-tTG-seronegative patients with CD-like enteropathy.