Detection of TRIM32 deletions in LGMD patients analyzed by a combined strategy of CGH array and massively parallel sequencing

Case report: A novel patient presenting TRIM32-related limb-girdle muscular dystrophy

Limb-girdle muscular dystrophy autosomal recessive 8 (LGMDR8) is a rare clinical manifestation caused by the presence of biallelic variants in the TRIM32 gene. We present the clinical, molecular, histopathological, and muscle magnetic resonance findings of a novel 63-years-old LGMDR8 patient of Italian origins, who went undiagnosed for 24 years. Clinical exome sequencing identified two TRIM32 missense variants, c.1181G > A p.(Arg394His) and c.1781G > A p.(Ser594Asp), located in the NHL1 and NHL4 structural domains, respectively, of the TRIM32 protein. We conducted a literature review of the clinical and instrumental data associated to the so far known 26 TRIM32 variants, carried biallelically by 53 LGMDR8 patients reported to date in 20 papers. Our proband's variants were previously identified only in three independent LGMDR8 patients in homozygosis, therefore our case is the first in literature to be described as compound heterozygous for such variants. Our report also provides additional data in support of their pathogenicity, since p.(Arg394His) is currently classified as a variant of uncertain significance, while p.(Ser594Asp) as likely pathogenic. Taken together, these findings might be useful to improve both the genetic counseling and the diagnostic accuracy of this rare neuromuscular condition.

TRIM32 biallelic defects cause limb-girdle muscular dystrophy R8: identification of two novel mutations and investigation of genotype-phenotype correlation

BACKGROUND

Limb-girdle muscular dystrophy R8 (LGMD R8) is a rare autosomal recessive muscle disease caused by TRIM32 gene biallelic defects. The genotype-phenotype correlation of this disease has been reported poorly. Here, we report a Chinese family with two female LGMD R8 patients.

METHODS

We performed whole-genome sequencing (WGS) and Sanger sequencing on the proband. Meanwhile, the function of mutant TRIM32 protein was analyzed by bioinformatics and experimental analysis. In addition, a summary of the reported TRIM32 deletions and point mutations and an investigation of genotype-phenotype correlation were performed through a combined analysis of the two patients and other cases reported in previous literature.

RESULTS

The two patients displayed typical symptoms of LGMD R8, which worsened during pregnancy. Genetic analysis by whole-genome sequencing (WGS) and Sanger sequencing showed that the patients were compound heterozygotes of a novel deletion (chr9.hg19:g.119431290_119474250del) and a novel missense mutation (TRIM32:c.1700A > G, p.H567R). The deletion encompassed 43 kb and resulted in the removal of the entire TRIM32 gene. The missense mutation altered the structure and further affected function by interfering with the self-association of the TRIM32 protein. Females with LGMD R8 showed less severe symptoms than males, and patients carrying two mutations in NHL repeats of the TRIM32 protein had earlier disease onset and more severe symptoms than other patients.

CONCLUSIONS

This research extended the spectrum of TRIM32 mutations and firstly provided useful data on the genotype-phenotype correlation, which is valuable for the accurate diagnosis and genetic counseling of LGMD R8.

A novel homozygous exon2 deletion of TRIM32 gene in a Chinese patient with sarcotubular myopathy: A case report and literature review

Sarcotubular myopathy (STM) is a rare autosomal recessive myopathy caused by TRIM32 gene mutations. It is predominantly characterized by the weakness of the proximal limb and mild to moderate elevation of creatine kinase levels. In this study, we describe a 50-year-old Chinese man who exhibited a proximal-to-distal weakness in the muscles of the lower limbs and who had difficulty standing up from a squat position. The symptoms gradually became more severe. He denied a history of cognitive or cardiological problems. The patient’s parents and children were healthy. Histopathological examination revealed dystrophic changes and irregular slit-shaped vacuoles containing amorphous materials. Whole-exome sequencing consisting of protein-encoding regions of 19,396 genes was performed, the results of which identified one novel homozygous 2kb deletion chr9.hg19: g.119460021_119461983del (exon2) in the TRIM32 gene. This was confirmed at the homozygous state with quantitative real-time polymerase chain reaction. Here, we present a Chinese case of STM with one novel mutation in TRIM32 and provide a brief summary of all known pathogenic mutations in TRIM32.

Myoneuropathic presentation of limb girdle muscular dystrophy R8 with a novel TRIM32 mutation

TRIM 32-related Limb Girdle Muscular Dystrophy (LGMD R8/2H) is a rare genetic muscle disease reported in fewer than 100 patients worldwide. Here, we report a male patient with progressive proximo-distal lower limb weakness with onset in the third decade who had mixed myopathic and neurogenic pattern in electrophysiology and muscle biopsy. Clinical exome sequencing revealed a homozygous pathogenic single base pair insertion in exon 2 of the TRIM32 gene confirming the diagnosis of LGMD R8. This is a novel frameshift mutation and one of the very few cases of LGMD R8 reported from India.

TRIM32 and Malin in Neurological and Neuromuscular Rare Diseases

Tripartite motif (TRIM) proteins are RING E3 ubiquitin ligases defined by a shared domain structure. Several of them are implicated in rare genetic diseases, and mutations in TRIM32 and TRIM-like malin are associated with Limb-Girdle Muscular Dystrophy R8 and Lafora disease, respectively. These two proteins are evolutionary related, share a common ancestor, and both display NHL repeats at their C-terminus. Here, we revmniew the function of these two related E3 ubiquitin ligases discussing their intrinsic and possible common pathophysiological pathways.

TRIM-NHL as RNA Binding Ubiquitin E3 Ligase (RBUL): Implication in development and disease pathogenesis

TRIM proteins are RING domain-containing modular ubiquitin ligases, unique due to their stimuli specific expression, localization, and turnover. The TRIM family consists of more than 76 proteins, including the TRIM-NHL sub-family which possesses RNA binding ability along with the inherent E3 Ligase activity, hence can be classified as a unique class of RNA Binding Ubiquitin Ligases (RBULs). Having these two abilities, TRIM-NHL proteins can play important role in a wide variety of cellular processes and their dysregulation can lead to complex and systemic pathological conditions. Increasing evidence suggests that TRIM-NHL proteins regulate RNA at the transcriptional and post-transcriptional level having implications in differentiation, development, and many pathological conditions. This review explores the evolving role of TRIM-NHL proteins as TRIM-RBULs, their ubiquitin ligase and RNA binding ability regulating cellular processes, and their possible role in different pathophysiological conditions.

Drosophila TRIM32 cooperates with glycolytic enzymes to promote cell growth

Cell growth and/or proliferation may require the reprogramming of metabolic pathways, whereby a switch from oxidative to glycolytic metabolism diverts glycolytic intermediates towards anabolic pathways. Herein, we identify a novel role for TRIM32 in the maintenance of glycolytic flux mediated by biochemical interactions with the glycolytic enzymes Aldolase and Phosphoglycerate mutase. Loss of Drosophila TRIM32, encoded by thin (tn), shows reduced levels of glycolytic intermediates and amino acids. This altered metabolic profile correlates with a reduction in the size of glycolytic larval muscle and brain tissue. Consistent with a role for metabolic intermediates in glycolysis-driven biomass production, dietary amino acid supplementation in tn mutants improves muscle mass. Remarkably, TRIM32 is also required for ectopic growth - loss of TRIM32 in a wing disc-associated tumor model reduces glycolytic metabolism and restricts growth. Overall, our results reveal a novel role for TRIM32 for controlling glycolysis in the context of both normal development and tumor growth.

Altered myogenesis and premature senescence underlie human TRIM32-related myopathy

TRIM32 is a E3 ubiquitin -ligase containing RING, B-box, coiled-coil and six C-terminal NHL domains. Mutations involving NHL and coiled-coil domains result in a pure myopathy (LGMD2H/STM) while the only described mutation in the B-box domain is associated with a multisystemic disorder without myopathy (Bardet-Biedl syndrome type11), suggesting that these domains are involved in distinct processes. Knock-out (T32KO) and knock-in mice carrying the c.1465G > A (p.D489N) involving the NHL domain (T32KI) show alterations in muscle regrowth after atrophy and satellite cells senescence. Here, we present phenotypical description and functional characterization of mutations in the RING, coiled-coil and NHL domains of TRIM32 causing a muscle dystrophy. Reduced levels of TRIM32 protein was observed in all patient muscle studied, regardless of the type of mutation (missense, single amino acid deletion, and frameshift) or the mutated domain. The affected patients presented with variable phenotypes but predominantly proximal weakness. Two patients had symptoms of both muscular dystrophy and Bardet-Biedl syndrome. The muscle magnetic resonance imaging (MRI) pattern is highly variable among patients and families. Primary myoblast culture from these patients demonstrated common findings consistent with reduced proliferation and differentiation, diminished satellite cell pool, accelerated senescence of muscle, and signs of autophagy activation.

Novel TRIM32 mutation in sarcotubular myopathy

Tripartite motif-containing protein 32 (TRIM32) is a member of the TRIM ubiquitin E3 ligases which ubiquitinates different substrates in muscle including sarcomeric proteins. Mutations in TRIM32 are associated with Limb-Girdle Muscular Dystrophy 2H. In a 66 old woman with disto-proximal myopathy, we identified a novel homozygous mutation of TRIM32 gene c.1781G > A (p. Ser594Asn) localised in the c-terminus NHL domain. Mutations of this domain have been also associated to Sarcotubular Myopathy (STM), a form of distal myopathy with peculiar features in muscle biopsy, now considered in the spectrum of LGMD2H. Muscle biopsy revealed severe abnormalities of the myofibrillar network with core like areas, lobulated fibres, whorled fibres and multiple vacuoles. Desmin and Myotilin stainings also pointed to accumulation as in Myofibrillar Myopathy. This report further confirms that STM and LGMD2H represent the same disorder and suggests to consider TRIM32 mutations in the genetic diagnosis of Sarcotubular Myopathy and Myofibrillar Myopathy.

Hybrid Capture-Based Next Generation Sequencing and Its Application to Human Infectious Diseases

This review describes target-enrichment approaches followed by next generation sequencing and their recent application to the research and diagnostic field of modern and past infectious human diseases caused by viruses, bacteria, parasites and fungi.

Thin is required for cell death in the Drosophila abdominal muscles by targeting DIAP1

In holometabolous insects, developmentally controlled programmed cell death (PCD) is a conserved process that destroys a subset of larval tissues for the eventual creation of new adult structures. This process of histolysis is relatively well studied in salivary gland and midgut tissues, while knowledge concerning larval muscle destruction is limited. Here, we have examined the histolysis of a group of Drosophila larval abdominal muscles called the dorsal external oblique muscles (DEOMs). Previous studies have defined apoptosis as the primary mediator of DEOM breakdown, whose timing is controlled by ecdysone signaling. However, very little is known about other factors that contribute to DEOM destruction. In this paper, we examine the role of thin (tn), which encodes for the Drosophila homolog of mammalian TRIM32, in the regulation of DEOM histolysis. We find that loss of Tn blocks DEOM degradation independent of ecdysone signaling. Instead, tn genetically functions in a pathway with the death-associated inhibitor of apoptosis (DIAP1), Dronc, and death-associated APAF1-related killer (Dark) to regulate apoptosis. Importantly, blocking Tn results in the absence of active Caspase-3 immunostaining, upregulation of DIAP1 protein levels, and inhibition of Dronc activation. DIAP1 and Dronc mRNA levels are not altered in tn mutants, showing that Tn acts post-transcriptionally on DIAP1 to regulate apoptosis. Herein, we also find that the RING domain of Tn is required for DEOM histolysis as loss of this domain results in higher DIAP1 levels. Together, our results suggest that the direct control of DIAP1 levels, likely through the E3 ubiquitin ligase activity of Tn, provides a mechanism to regulate caspase activity and to facilitate muscle cell death.

The italian limb girdle muscular dystrophy registry: Relative frequency, clinical features, and differential diagnosis

INTRODUCTION

Limb girdle muscular dystrophies (LGMDs) are characterized by high molecular heterogeneity, clinical overlap, and a paucity of specific biomarkers. Their molecular definition is fundamental for prognostic and therapeutic purposes.

METHODS

We created an Italian LGMD registry that included 370 molecularly defined patients. We reviewed detailed retrospective and prospective data and compared each LGMD subtype for differential diagnosis purposes.

RESULTS

LGMD types 2A and 2B are the most frequent forms in Italy. The ages at disease onset, clinical progression, and cardiac and respiratory involvement can vary greatly between each LGMD subtype. In a set of extensively studied patients, targeted next-generation sequencing (NGS) identified mutations in 36.5% of cases.

CONCLUSION

Detailed clinical characterization combined with muscle tissue analysis is fundamental to guide differential diagnosis and to address molecular tests. NGS is useful for diagnosing forms without specific biomarkers, although, at least in our study cohort, several LGMD disease mechanisms remain to be identified. Muscle Nerve 55: 55-68, 2017.

TRIM32 ubiquitin E3 ligase, one enzyme for several pathologies: From muscular dystrophy to tumours

TRIM32 is a member of the TRIpartite Motif family characterised by the presence of an N-terminal three-domain-module that includes a RING domain, which confers E3 ubiquitin ligase activity, one or two B-box domains and a Coiled-Coil region that mediates oligomerisation. Several TRIM32 substrates were identified including muscular proteins and proteins involved in cell cycle regulation and cell motility. As ubiquitination is a versatile post-translational modification that can affect target turnover, sub-cellular localisation or activity, it is likely that diverse substrates may be differentially affected by TRIM32-mediated ubiquitination, reflecting its multi-faceted roles in muscle physiology, cancer and immunity. With particular relevance for muscle physiology, mutations in TRIM32 are associated with autosomal recessive Limb-Girdle Muscular Dystrophy 2H, a muscle-wasting disease with variable clinical spectrum ranging from almost asymptomatic to wheelchair-bound patients. In this review, we will focus on the ability of TRIM32 to mark specific substrates for proteasomal degradation discussing how the TRIM32-proteasome axis may (i) be important for muscle homeostasis and for the pathogenesis of muscular dystrophy; and (ii) define either an oncogenic or tumour suppressive role for TRIM32 in the context of different types of cancer.

Prenatal diagnosis of congenital myopathies and muscular dystrophies

Congenital myopathies and muscular dystrophies constitute a genetically and phenotypically heterogeneous group of rare inherited diseases characterized by muscle weakness and atrophy, motor delay and respiratory insufficiency. To date, curative care is not available for these diseases, which may severely affect both life-span and quality of life. We discuss prenatal diagnosis and genetic counseling for families at risk, as well as diagnostic possibilities in sporadic cases.

Laminin α2 Deficiency-Related Muscular Dystrophy Mimicking Emery-Dreifuss and Collagen VI related Diseases

Background: Laminin α2 deficient congenital muscular dystrophy, caused by mutations in the LAMA2 gene, is characterized by early muscle weakness associated with abnormal white matter signal on cerebral MRI.

Objective: To report on 4 patients with LAMA2 gene mutations whose original clinical features complicated the diagnosis strategy.

Methods: Clinical, electrophysiological, muscle imaging and histopathological data were retrospectively collected from all patients. DNA samples were analysed by next-generation sequencing or direct gene sequencing. Laminin α2 was analysed by western-blot and immunohistochemistry.

Results: The four patients achieved independent walking. All had proximal muscle weakness with scapular winging and prominent joint contractures without peripheral neuropathy. During follow-up, two patients suffered from refractory epilepsy associated with brain leukoencephalopathy in one, polymicrogyria and lissencephaly without white matter changes in the other. In two patients, the distribution of fatty infiltration resembles that of collagen-VI related myopathies. Dilated cardiomyopathy contstartabstractwith conduction defects, suggestive of Emery-Dreifuss myopathy, emerged in two of them within the 4th decade. Molecular diagnosis remained elusive for many years. Finally, targeted capture-DNA sequencing unveiled the involvement of the LAMA2 gene in two families, and led us to further identify LAMA2 mutations in the remaining family using Sanger sequencing.

Conclusions: This report extends the clinical and radiological features of partial Laminin α2 deficiency since patients showed atypical manifestations including dilated cardiomyopathy with conduction defects in 2, epilepsy in 2, one of whom also had sole cortical brain abnormalities. Importantly, clinical findings and muscle imaging initially pointed to collagen-VI related disorders and Emery-Dreifuss muscular dystrophy.