Background Tubular aggregate myopathies (TAMs) are muscle disorders characterised by abnormal accumulations of densely packed single-walled or doublewalled membrane tubules in muscle fibres. Recently, STIM1, encoding a major calcium sensor of the endoplasmic reticulum, was identified as a TAM gene. Methods The present study aims to define the clinical, histological and ultrastructural phenotype of tubular aggregate myopathy and to assess the STIM1 mutation spectrum. Results We describe six new TAM families harbouring one known and four novel STIM1 mutations. All identified mutations are heterozygous missense mutations affecting highly conserved amino acids in the calcium-binding EFhand domains, demonstrating the presence of a mutation hot spot for TAM. We show that the mutations induce constitutive STIM1 clustering, strongly suggesting that calcium sensing and consequently calcium homoeostasis is impaired. Histological and ultrastructural analyses define a common picture with tubular aggregates labelled with Gomori trichrome and Nicotinamide adenine dinucleotide (NADH) tetrazolium reductase, substantiating their endoplasmic reticulum origin. The aggregates were observed in both fibre types and were often accompanied by nuclear internalisation and fibre size variability. The phenotypical spectrum ranged from childhood onset progressive muscle weakness and elevated creatine kinase levels to adultonset myalgia without muscle weakness and normal CK levels. Conclusions The present study expands the phenotypical spectrum of STIM1-related tubular aggregate myopathy. STIM1 should therefore be considered for patients with tubular aggregate myopathies involving either muscle weakness or myalgia as the first and predominant clinical sign.

No abstract

Limb-girdle muscular dystrophies (LGMDs) are genetically heterogeneous and the diagnostic work-up including conventional genetic testing using Sanger sequencing remains complex and often unsatisfactory. We performed targeted sequencing of 23 LGMD-related genes and 15 genes in which alterations result in a similar phenotype in 58 patients with genetically unclassified LGMDs. A genetic diagnosis was possible in 19 of 58 patients (33 %). LGMD2A was the most common form, followed by LGMD2L and LGMD2I. In two patients, pathogenic mutations were identified in genes that are not classified as LGMD genes (glycogen branching enzyme and valosin-containing protein). Thus, a focused next-generation sequencing-based gene panel is a rather satisfactory tool for the diagnosis in unclassified LGMDs.

Carnitine palmitoyltransferase (CPT) catalyzes the transfer of long- and medium-chain fatty acids from cytoplasm into mitochondria, where oxidation of fatty acids takes place. Deficiency of CPT enzyme is associated with rare diseases of fatty acid metabolism. CPT is present in two subforms: CPT I at the outer mitochondrial membrane and carnitine palmitoyltransferase II (CPT II) inside the mitochondria. Deficiency of CPT II results in the most common inherited disorder of long-chain fatty acid oxidation affecting skeletal muscle. There is a lethal neonatal form, a severe infantile hepato-cardio-muscular form, and a rather mild myopathic form characterized by exercise-induced myalgia, weakness, and myoglobinuria. Total CPT activity (CPT I + CPT II) in muscles of CPT II-deficient patients is generally normal. Nevertheless, in some patients, not detectable to reduced total activities are also reported. CPT II protein is also shown in normal concentration in patients with normal CPT enzymatic activity. However, residual CPT II shows abnormal inhibition sensitivity towards malonyl-CoA, Triton X-100 and fatty acid metabolites in patients. Genetic studies have identified a common p.Ser113Leu mutation in the muscle form along with around 100 different rare mutations. The biochemical consequences of these mutations have been controversial. Hypotheses include lack of enzymatically active protein, partial enzyme deficiency and abnormally regulated enzyme. The recombinant enzyme experiments that we recently conducted have shown that CPT II enzyme is extremely thermoliable and is abnormally inhibited by different emulsifiers and detergents such as malonyl-CoA, palmitoyl-CoA, palmitoylcarnitine, Tween 20 and Triton X-100. Here, we present a conceptual overview on CPT II deficiency based on our own findings and on results from other studies addressing clinical, biochemical, histological, immunohistological and genetic aspects, as well as recent advancements in diagnosis and therapeutic strategies in this disorder.

Background.-Mitochondrial diseases are a heterogeneous group of diseases with different phenotypes and genotypes. Headache and, particularly migraine, seems to occur often in patients with MELAS and in patients with CPEO phenotypes. The International Classification of Headache Disorders (ICHD-3 beta) has classified headache as a secondary entity only in MELAS patients. Other headache phenotypes in mitochondrial diseases are not considered in ICHD-3beta. In this study, we analyzed headache phenomenology in a large group of patients with mitochondrial disorders.Methods.-A cross-sectional questionnaire-based study on 85 patients with mitochondrial disease with different genotypes and phenotypes was conducted between 2010 and 2011. A structured headache questionnaire according to ICHD-2 was used followed by a telephone interview by a headache expert. Prevalence and characteristics of headache could be analyzed in 42 patients. Headache diagnosis was correlated with genotypes and phenotypes. In addition, the mtDNA haplotype H was analyzed.Results.-Headache was reported in 29/42 (70%; 95% CI, from 55.1 to 83.0%) of the patients. Tension-type headache (TTH) showed the highest prevalence in 16/42 (38%; 95% CI, from 23.4 to 52.8%) patients, followed by migraine and probable migraine in 12/42 (29%; 95% CI, from 14.9 to 42.2%) patients. Nine of the 42 (21%; 95% CI, from 9 to 33.8%) patients reported two different headache types. Patients with the mtDNA mutation m.3243A > G (n 5 8) and MELAS (n 5 7) showed the highest prevalence of headaches (88% and 85%, respectively). In patients with the CPEO phenotype (n 5 32), headache occurred in 14/18 (78%; 95% CI, from 58.6 to 97%) of patients with single deletions, and in 7/13 (54%; 95% CI, from 26.7 to 80.9%) patients with multiple mtDNA deletions. There were no association between the mtDNA haplotype Hand the headache-diagnosis.Conclusions.-The prevalence of headache was higher in patients with mitochondrial diseases than reported in the general population. In all phenotype and genotype groups, TTH was more frequent than migraine. The data also show that the current ICHD-3 beta exclusively focused on MELAS syndrome as vasculopathy does not consider the broader spectrum of headache phenotypes in mitochondrial disorders.