Carola Hedberg

Hereditary myopathy with early respiratory failure: occurrence in various populations

Objective Several families with characteristic features of hereditary myopathy with early respiratory failure (HMERF) have remained without genetic cause. This international study was initiated to clarify epidemiology and the genetic underlying cause in these families, and to characterise the phenotype in our large cohort. Methods DNA samples of all currently known families with HMERF without molecular genetic cause were obtained from 12 families in seven different countries. Clinical, histopathological and muscle imaging data were collected and five biopsy samples made available for further immunohistochemical studies. Genotyping, exome sequencing and Sanger sequencing were used to identify and confirm sequence variations. Results All patients with clinical diagnosis of HMERF were genetically solved by five different titin mutations identified. One mutation has been reported while four are novel, all located exclusively in the FN3 119 domain (A150) of A-band titin. One of the new mutations showed semirecessive inheritance pattern with subclinical myopathy in the heterozygous parents. Typical clinical features were respiratory failure at mid-adulthood in an ambulant patient with very variable degree of muscle weakness. Cytoplasmic bodies were retrospectively observed in all muscle biopsy samples and these were reactive for myofibrillar proteins but not for titin. Conclusions We report an extensive collection of families with HMERF with five different mutations in exon 343 of TTN, which establishes this exon as the primary target for molecular diagnosis of HMERF. Our relatively large number of new families and mutations directly implies that HMERF is not extremely rare, not restricted to Northern Europe and should be considered in undetermined myogenic respiratory failure.

Autosomal dominant myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy 7 is caused by a DES mutation

Using exome sequencing we searched for the genetic cause of autosomal dominant myofibrillar myopathy with arrhythmogenic right ventricular cardiomyopathy (ARVC) in a Swedish family. A heterozygous C-to-T transition, c.1255C>T, p.Pro419Ser in the desmin gene on chromosome 2q35, was identified. Previous studies had demonstrated linkage to chromosome 10q22.3, but no causative mutation had been found in that region. Sanger sequencing of DNA from 17 family members confirmed the heterozygous c.1255C>T desmin mutation in seven out of ten family members that had been classified as affected in the previous study. Our new results demonstrate the usefulness of next-generation sequencing, and the diagnostic difficulties with some forms of dominantly inherited muscle diseases as they can display a wide clinical and morphological variability even within a given family.

Childhood onset tubular aggregate myopathy associated with de novo STIM1 mutations

Abstract We investigated three unrelated patients with tubular-aggregate myopathy and slowly progressive muscle weakness manifesting in the first years of life. All patients showed type 1 muscle fiber predominance and hypotrophy of type 2 fibers. Tubular aggregates were abundant. In all three patients mutations were identified in the gene STIM1, and the mutations were found to be de novo in all patients. In one of the patients the mutation was identified by exome sequencing. Two patients harbored the previously described mutation c.326A>G p.(His109Arg), while the third patient had a novel mutation c.343A>T p.(Ile115Phe). Taking our series together with previously published cases, the c.326A>G p.(His109Arg) seems to be a hotspot mutation that is characteristically related to early onset muscle weakness.

Hereditary myopathy with early respiratory failure is caused by mutations in the titin FN3 119 domain

Sir, Hereditary myopathy with early respiratory failure (HMERF) is a neuromuscular disease associated with aggregation of various proteins in muscle fibres and muscle degeneration (Fig. 1) and was described in detail in several families by Edstrom et al. (1990). Linkage analyses indicated that the disease locus was in the distal part of the long arm of chromosome 2 (Nicolao et al. , 1999). Titin was a candidate gene and a missense variant that segregated with the disease in …

B3GALNT2 is a gene associated with congenital muscular dystrophy with brain malformations

Congenital muscular dystrophies associated with brain malformations are a group of disorders frequently associated with aberrant glycosylation of α-dystroglycan. They include disease entities such a Walker–Warburg syndrome, muscle–eye–brain disease and various other clinical phenotypes. Different genes involved in glycosylation of α-dystroglycan are associated with these dystroglycanopathies. We describe a 5-year-old girl with psychomotor retardation, ataxia, spasticity, muscle weakness and increased serum creatine kinase levels. Immunhistochemistry of skeletal muscle revealed reduced glycosylated α-dystroglycan. Magnetic resonance imaging of the brain at 3.5 years of age showed increased T2 signal from supratentorial and infratentorial white matter, a hypoplastic pons and subcortical cerebellar cysts. By whole exome sequencing, the patient was identified to be compound heterozygous for a one-base duplication and a missense mutation in the gene B3GALNT2 (β-1,3-N-acetylgalactosaminyltransferase 2; B3GalNAc-T2). This patient showed a milder phenotype than previously described patients with mutations in the B3GALNT2 gene.

Myopathy in a woman and her daughter associated with a novel splice site MTM1 mutation.

We have investigated a woman and her daughter with an early onset, slowly progressive myopathy. Muscle biopsy showed in both cases severe atrophy with marked fatty replacement. Frequent fibers with internalized nuclei were present but no typical features of centronuclear myopathy. There were also many fibers with deep invaginations of the plasma membrane. The presence of necklace fibers provided clue to correct genetic diagnosis. Both patients had a novel heterozygous splice site mutation in the myotubularin gene, MTM1 (c.867+1G>T). Analysis of MTM1 cDNA revealed that the mutation resulted in aberrant splicing with variable exon skipping. The expression of normal transcripts was markedly reduced and there was reduced expression of myotubularin protein. Although the expression of the allele without the mutation was reduced we did not obtain evidence of skewed X-chromosome inactivation. Other factors than skewed X-inactivation may cause allele inactivation and manifestation of severe myopathy in heterozygous carriers of pathogenic MTM1 mutations.

Molecular classification of spontaneous endometrial adenocarcinomas in BDII rats

Female rats of the BDII/Han inbred strain are prone to spontaneously develop endometrial carcinomas (EC) that in cell biology and pathogenesis are very similar to those of human. Human EC are classified into two major groups: Type I displays endometroid histology, is hormone-dependent, and characterized by frequent microsatellite instability and PTEN, K-RAS, and CTNNB1 (beta-Catenin) mutations; Type II shows non-endometrioid histology, is hormone-unrelated, displays recurrent TP53 mutation, CDKN2A (P16) inactivation, over-expression of ERBB2 (Her2/neu), and reduced CDH1 (Cadherin 1 or E-Cadherin) expression. However, many human EC have overlapping clinical, morphologic, immunohistochemical, and molecular features of types I and II. The EC developed in BDII rats can be related to type I tumors, since they are hormone-related and histologically from endometrioid type. Here, we combined gene sequencing (Pten, Ifr1, and Ctnnb1) and real-time gene expression analysis (Pten, Cdh1, P16, Erbb2, Ctnnb1, Tp53, and Irf1) to further characterize molecular alterations in this tumor model with respect to different subtypes of EC in humans. No mutation in Pten and Ctnnb1 was detected, whereas three tumors displayed sequence aberrations of the Irf1 gene. Significant down regulation of Pten, Cdh1, p16, Erbb2, and Ctnnb1 gene products was found in the tumors. In conclusion, our data suggest that molecular features of spontaneous EC in BDII rats can be related to higher-grade human type I tumors and thus, this model represents an excellent experimental tool for research on this malignancy in human.

Hereditary myopathy with early respiratory failure is associated with misfolding of the titin fibronectin III 119 subdomain

Hereditary myopathy with early respiratory failure is a rare disease with muscle weakness and respiratory failure as early symptoms. Muscle pathology is characterized by the presence of multiple cytoplasmic bodies and other protein aggregates in muscle fibers. The disease is associated with mutations in the titin gene (TTN). All patients harbor mutations located in exon 343 in the TTN gene that codes for the fibronectin III domain 119 (FN3 119) in the 10th motif of the 11-element motif A-band super-repeat. We investigated how such disease-causing mutations affect the biochemical behavior of this titin domain. All five disease-causing amino acid changes analyzed by us (p.P30068R, p.C30071R, p.W30088R, p.W30088C and p.P30091L) resulted in impaired FN3 119 domain solubility. In contrast, amino acid changes associated with common SNPs (p.V30076I, p.R30107C and p.S30125F) did not have this effect. In silico analyses further support the notion that disease-causing mutations impair proper folding of the FN3 119 domain. The results suggest that hereditary myopathy with early respiratory failure is caused by defective protein folding.

SKY analysis revealed recurrent numerical and structural chromosome changes in BDII rat endometrial carcinomas

BackgroundGenomic alterations are common features of cancer cells, and some of these changes are proven to be neoplastic-specific. Such alterations may serve as valuable tools for diagnosis and classification of tumors, prediction of clinical outcome, disease monitoring, and choice of therapy as well as for providing clues to the location of crucial cancer-related genes.Endometrial carcinoma (EC) is the most frequently diagnosed malignancy of the female genital tract, ranking fourth among all invasive tumors affecting women. Cytogenetic studies of human ECs have not produced very conclusive data, since many of these studies are based on karyotyping of limited number of cases and no really specific karyotypic changes have yet been identified. As the majority of the genes are conserved among mammals, the use of inbred animal model systems may serve as a tool for identification of underlying genes and pathways involved in tumorigenesis in humans. In the present work we used spectral karyotyping (SKY) to identify cancer-related aberrations in a well-characterized experimental model for spontaneous endometrial carcinoma in the BDII rat tumor model.ResultsAnalysis of 21 experimental ECs revealed specific nonrandom numerical and structural chromosomal changes. The most recurrent numerical alterations were gains in rat chromosome 4 (RNO4) and losses in RNO15. The most commonly structural changes were mainly in form of chromosomal translocations and were detected in RNO3, RNO6, RNO10, RNO11, RNO12, and RNO20. Unbalanced chromosomal translocations involving RNO3p was the most commonly observed structural changes in this material followed by RNO11p and RNO10 translocations.ConclusionThe non-random nature of these events, as documented by their high frequencies of incidence, is suggesting for dynamic selection of these changes during experimental EC tumorigenesis and therefore for their potential contribution into development of this malignancy. Comparative molecular analysis of the identified genetic changes in this tumor model with those reported in the human ECs may provide new insights into underlying genetic changes involved in EC development and tumorigenesis.

A.P.7

Hereditary myopathy with early respiratory failure (HMERF) is a rare disease with muscle weakness and respiratory failure as early symptoms. Muscle pathology is characterized by the presence of multiple cytoplasmic bodies and other protein aggregates in muscle fibers. These protein aggregates are composed of multiple proteins including titin, aB-crystallin, actin, myotilin, desmin and others. Previous reports have described mutations in A-band titin ( TTN ) gene associated with HMERF. All patients harbor mutations located in exon 343 in the TTN gene that codes for the fibronectin III domain 119 (FN3 119) in the 10th motif of the 11-element motif A-band super-repeat. Based on the pathological findings in HMERF of protein aggregates in muscle fibers, we investigated if disease-causing mutations affect the biochemical behavior of this titin domain. All five disease-causing amino acid changes analyzed by us (p.P30068R, p.C30071R, p.W30088R, p.W30088C and p.P30091L) resulted in impaired FN3 119 domain solubility. In contrast, amino acid changes associated with common SNPs (p.V30076I, p.R30107C and p.S30125F) did not have this effect. In silico analyses further support the notion that disease-causing mutations impair proper folding of the FN3 119 domain. Our results suggest that HMERF is caused by defective protein folding. We speculate that the FN3 119 domain could be important for protein–protein interaction that could explain why all identified mutations causing HMERF are located in this particular domain.