Mutation update and genotype-phenotype correlations of novel and previously described mutations in TPM2 and TPM3 causing congenital myopathies

Mutations affecting skeletal muscle isoforms of the tropomyosin genes may cause nemaline myopathy, cap myopathy, core-rod myopathy, congenital fiber-type disproportion, distal arthrogryposes, and Escobar syndrome. We correlate the clinical picture of these diseases with novel (19) and previously reported (31) mutations of the TPM2 and TPM3 genes. Included are altogether 93 families: 53 with TPM2 mutations and 40 with TPM3 mutations. Thirty distinct pathogenic variants of TPM2 and 20 of TPM3 have been published or listed in the Leiden Open Variant Database (http://www.dmd.nl/). Most are heterozygous changes associated with autosomal-dominant disease. Patients with TPM2 mutations tended to present with milder symptoms than those with TPM3 mutations, DA being present only in the TPM2 group. Previous studies have shown that five of the mutations in TPM2 and one in TPM3 cause increased Ca2+ sensitivity resulting in a hypercontractile molecular phenotype. Patients with hypercontractile phenotype more often had contractures of the limb joints (18/19) and jaw (6/19) than those with nonhypercontractile ones (2/22 and 1/22), whereas patients with the non-hypercontractile molecular phenotype more often (19/22) had axial contractures than the hypercontractile group (7/19). Our in silico predictions show that most mutations affect tropomyosin–actin association or tropomyosin head-to-tail binding

Abnormal distribution of inositol 1,4,5-trisphosphate receptors in human muscle can be related to altered calcium signals and gene expression in Duchenne dystrophy-derived cells

Inositol 1,4,5-trisphosphate (IP3) receptors (IP3Rs) drive calcium signals involved in skeletal muscle excitation-transcription coupling and plasticity; IP3R subtype distribution and downstream events evoked by their activation have not been studied in human muscle nor has their possible alteration in Duchenne muscular dystrophy (DMD). We studied the expression and localization of IP3R subtypes in normal and DMD human muscle and in normal (RCMH) and dystrophic (RCDMD) human muscle cell lines. In normal muscle, both type 1 IP3Rs (IP3R1) and type 2 IP3Rs (IP3R2) show a higher expression in type II fibers, whereas type 3 IP3Rs (IP3R3) show uniform distribution. In DMD biopsies, all fibers display a homogeneous IP3R2 label, whereas 24 ± 7% of type II fibers have lost the IP3R1 label. RCDMD cells show 5-fold overexpression of IP3R2 and down-regulation of IP3R3 compared with RCMH cells. A tetanic stimulus induces IP 3-dependent slow Ca2+ transients significantly larger and faster in RCDMD c

Argentine consensus on late-onset Pompe's disease

Pompe's disease (PD) is an infrequent metabolic autosomic recessive disorder produced by the lack or deficiency of the acid alpha-glucosidase lysosomal enzyme in tissues of involved individuals. Delayed-onset PD is considered whenever symptoms onset start after one year of age. We present an update of the recommendations for the management of delayed-onset PD, taking as reference the guidelines from the Argentine Consensus for diagnosis, treatment and follow-up of PD published in 2013. The present consensus gathered several experts in PD in the areas of internal medicine, laboratory diagnosis, neuropathology, pulmonology, nutrition, neurology, metabolic and neuromuscular disorders as well as rehabilitation to perform an update of the literature of delayed-onset PD, with special attention on relevant information published within the last 4 years. The entire working group approved the final version of the consensus. Each participant provided a declaration of conflict of interest. As a result, it is an update of the previous Argentine PD Consensus with focus on the delayed-onset presentation of the disease. Being such infrequent disorder, available data were rather limited and thus, the recommendations represent expert opinion

myotilin Mutation Found in Second Pedigree with LGMD1A

Limb-girdle muscular dystrophy 1A (LGMD1A [MIM 159000]) is an autosomal dominant form of muscular dystrophy characterized by adult onset of proximal weakness progressing to distal muscle weakness. We have reported elsewhere a mutation in the myotilin gene in a large, North American family of German descent. Here, we report the mutation screening of an additional 86 families with a variety of neuromuscular pathologies. We have identified a new myotilin mutation in an Argentinian pedigree with LGMD1 that is predicted to result in the conversion of serine 55 to phenylalanine (S55F). This mutation has not been found in 392 control chromosomes and is located in the unique N-terminal domain of myotilin, only two residues from the T57I mutation reported elsewhere. Both T57I and S55F are located outside the α-actinin and γ-filamin binding sites within myotilin. The identification of two independent pedigrees with the same disease, each bearing a different mutation in the same gene, has long been the gold standard for establishing a causal relationship between defects in a gene and the resultant disease. As a description of the second known pedigree with LGMD1A, this finding constitutes that gold standard of proof that mutations in the myotilin gene cause LGMD1A

Morphological spectrum and clinical features of myopathies with tubular aggregates

Tubular aggregates (TAs) are aggregates of densely packed tubules in human skeletal muscle fibers with particular histochemical and ultrastructural features that most probably arise from the sarcoplasmic reticulum. Some studies have shown an additional mitochondrial origin of TAs. We studied the histopathological spectrum and clinical features in a large cohort of patients with TAs in their muscle biopsy (106 biopsies), derived from our muscle biopsy archive (15,412 biopsies in total). In particular, we examined light microscopic, enzyme histochemical, immunohistochemical and ultrastructural features in the muscle biopsies, as well as the patients' clinical data. We found TAs in 0.5% of all muscle biopsies. Based on the size of TAs, we identified two sub-groups: (1) myopathies with large TAs (29 biopsies) in type 2 fibers and sometimes also in type 1 fibers, absence of any other associated disorder, and a familial history in half of the cases, and (2) myopathies with small TAs (77 biopsies), exclusively in type 2 fibers, presence of another associated disease in the majority of patients and mostly no familial history. In the sub-group with large TAs, we observed a high variability of ultrastructural changes. The most frequent clinical symptom in both groups was limb muscle weakness. No significant differences in clinical presentation, age at onset or disease duration at the time of biopsy were found between the two groups. In conclusion, myopathies with TAs can be sub-divided into a group with large TAs, probably corresponding to the so-called primary TA myopathies, and into a group with small TAs as a feature of another underlying condition.magna cum laude; Thesis to obtain "Dr. med." title in Germany, Faculty of Medicine.status: publishe

Morphological spectrum and clinical features of myopathies with tubular aggregates

Tubular aggregates (TAs) are aggregates of densely packed tubules in human skeletal muscle fibers with particular histochemical and ultrastructural features that most probably arise from the sarcoplasmic reticulum. Some studies have shown an additional mitochondrial origin of TAs. We studied the histopathological spectrum and clinical features in a large cohort of patients with TAs in their muscle biopsy (106 biopsies), derived from our muscle biopsy archive (15,412 biopsies in total). In particular, we examined light microscopic, enzyme histochemical, immunohistochemical and ultrastructural features in the muscle biopsies, as well as the patients’ clinical data. We found TAs in 0.5% of all muscle biopsies. Based on the size of TAs, we identified two sub-groups: (1) myopathies with large TAs (29 biopsies) in type 2 fibers and sometimes also in type 1 fibers, absence of any other associated disorder, and a familial history in half of the cases, and (2) myopathies with small TAs (77 biopsies), exclusively in type 2 fibers, presence of another associated disease in the majority of patients and mostly no familial history. In the sub-group with large TAs, we observed a high variability of ultrastructural changes. The most frequent clinical symptom in both groups was limb muscle weakness. No significant differences in clinical presentation, age at onset or disease duration at the time of biopsy were found between the two groups. In conclusion, myopathies with TAs can be sub-divided into a group with large TAs, probably corresponding to the so-called primary TA myopathies, and into a group with small TAs as a feature of another underlying condition