TPM3 deletions cause a hypercontractile congenital muscle stiffness phenotype.

OBJECTIVE: Mutations in TPM3, encoding Tpm3.12, cause a clinically and histopathologically diverse group of myopathies characterized by muscle weakness. We report two patients with novel de novo Tpm3.12 single glutamic acid deletions at positions ΔE218 and ΔE224, resulting in a significant hypercontractile phenotype with congenital muscle stiffness, rather than weakness, and respiratory failure in one patient. METHODS: The effect of the Tpm3.12 deletions on the contractile properties in dissected patient myofibers was measured. We used quantitative in vitro motility assay to measure Ca(2+) sensitivity of thin filaments reconstituted with recombinant Tpm3.12 ΔE218 and ΔE224. RESULTS: Contractility studies on permeabilized myofibers demonstrated reduced maximal active tension from both patients with increased Ca(2+) sensitivity and altered cross-bridge cycling kinetics in ΔE224 fibers. In vitro motility studies showed a two-fold increase in Ca(2+) sensitivity of the fraction of filaments motile and the filament sliding velocity concentrations for both mutations. INTERPRETATION: These data indicate that Tpm3.12 deletions ΔE218 and ΔE224 result in increased Ca(2+) sensitivity of the troponin-tropomyosin complex, resulting in abnormally active interaction of the actin and myosin complex. Both mutations are located in the charged motifs of the actin-binding residues of tropomyosin 3, thus disrupting the electrostatic interactions that facilitate accurate tropomyosin binding with actin necessary to prevent the on-state. The mutations destabilize the off-state and result in excessively sensitized excitation-contraction coupling of the contractile apparatus. This work expands the phenotypic spectrum of TPM3-related disease and provides insights into the pathophysiological mechanisms of the actin-tropomyosin complex.

Measurement of cerebral microvascular compliance in a model of atherosclerosis with optical coherence tomography.

Optical coherence tomography (OCT) has recently been used to produce 3D angiography of microvasculature and blood flow maps of large vessels in the rodent brain in-vivo. However, use of this optical method for the study of cerebrovascular disease has not been fully explored. Recent developments in neurodegenerative diseases has linked common cardiovascular risk factors to neurodegenerative risk factors hinting at a vascular hypothesis for the development of the latter. Tools for studying cerebral blood flow and the myogenic tone of cerebral vasculature have thus far been either highly invasive or required ex-vivo preparations therefore not preserving the delicate in-vivo conditions. We propose a novel technique for reconstructing the flow profile over a single cardiac cycle in order to evaluate flow pulsatility and vessel compliance. A vascular model is used to simulate changes in vascular compliance and interpret OCT results. Comparison between atherosclerotic and wild type mice show a trend towards increased compliance in the smaller arterioles of the brain (diameter < 80µm) in the disease model. These results are consistent with previously published ex-vivo work confirming the ability of OCT to investigate vascular dysfunction.

A novel autosomal recessive limb-girdle muscular dystrophy with quadriceps atrophy maps to 11p13-p12.

Limb-girdle muscular dystrophies (LGMD) are a heterogeneous group of pathologies. We have identified a cohort of 14 French-Canadian patients from eight different families displaying a novel form of LGMD with an autosomal recessive inheritance. These patients share some features with previously described cases of 'quadriceps myopathy' that evolved into an LGMD. All demonstrate quadriceps femoris asymmetrical atrophy. Creatine kinase values were variable from normal to 6000 U/l. Clinical evaluations and MRI studies demonstrate a variable intrafamilial and interfamilial phenotype. Asymmetrical muscle involvement was clinically observed and confirmed by imaging. MRI studies suggest that the hamstrings and the adductor magnus are the first limb muscles to demonstrate fatty infiltration. Muscle pathology shows no sign of active inflammation but increased endomysial connective tissue associated with basal lamina duplication and collagen disorganization. A genome-wide scan using the two largest families uncovered linkage to marker D11S1360 on chromosome 11p12 [multipoint logarithm of the odds (LOD) score of 2.78]. Further genotyping for the eight families confirmed linkage to this new LGMD locus (multipoint LOD score of 4.56). Fine mapping subsequently defined a less than 3.3 cM candidate interval on 11p13-p12. Haplotype analysis of carrier chromosomes suggests that the most frequent mutation may account for up to 81.3% of French-Canadian mutations. In this study, we describe the chromosomal locus of a new form of recessive LGMD with prominent quadriceps femoris atrophy.