Myotilinopathy is one of the intermediate filament human disorders associated with mutations in the myotilin gene (MYOT). Myolinopathies include autosomal dominant limb girdle muscular dystrophy type 1A (LGMD1A) and a subgroup of myofibrillar myopathy (MFM) associated with myotilin mutations (MFM/MYOT).
- Muscle weakness initially in distal or proximal leg muscles, eventually spreading to other muscle groups of the lower and upper extremities
- Respiratory failure
- Peripheral neuropathy
Myotilinopathy is associated with mutations in the myotilin gene (MYOT).
Muscle biopsy in affected individuals showed marked variation in fibre size and increased number of internal nuclei. Atrophic rounded fibres of either histochemical type often clustered in small groups . Polymorphic inclusions of varying size and shape were seen in multiple muscle fibres of patients. These inclusions appear as non-hyaline irregular patches located in the centre of the fibre or in the subsarcolemmal space. They appear pink with HE and dark-blue with the modified trichrome Gomori stain. Single or multiple hyaline inclusions staining bright pink with HE and blue–red or red–purple with the modified trichrome Gomori stain were also observed; they varied in shape and size and lacked oxidative and ATPase activity. Some hyaline structures were congophilic.
Singel-and double-labelling immunofluorescence and confocal miscroscopie
Cryostat sections were stained with saturated solution of Sudan black B (Merck, Darmstadt, Denmark) for 30 min to block autofluorescence of lipofuscin granules, rinsed in 70% ethanol and washed in distilled water. The sections were incubated at 4°C overnight with mouse monoclonal anti-myotilin antibody (Novocastra) at 1 : 150 dilution and either rabbit polyclonal anti-ubiquitin (Dako, Barcelona, Spain) or goat anti-clusterin antibody (Chemicon, Temecula, CA) at dilutions of 1 : 100 or 1 : 200, in a vehicle solution composed of Tris buffer, pH 7.2, containing 15 mmol/l NaN3, and protein (Dako). Secondary antibodies were Alexa488 anti-goat and Alexa546 anti-mouse or anti-rabbit (all from Molecular Probes, Eugene, OR) at 1 : 400 dilution. After washing with PBS, the sections were incubated in a cocktail of secondary antibodies in the same vehicle solution for 45 min at room temperature. After washing in PBS, the sections were mounted in immuno-Fluore Mounting medium (ICN Biomedicals, Costa Mesa, CA), sealed and dried overnight. The sections were examined under a Leica TCS-SL confocal microscope. Sections incubated with just one primary antibody and the corresponding secondary antibody, and sections incubated with the secondary antibodies alone, served as controls.
Genomic DNA is extracted from anticoagulated blood using the Wizard™ Genomic DNA Purification Kit (Promega) and used as template for amplification of MYOT exons with intronic primers designed for this purpose (primer sequences are available on request). Amplification is carried out using an optimal procedure designed for each separate segment. PCR-produced DNA is purified using QIAquick PCR Purification Kit (Qiagen, Valencia, CA) and sequenced in both directions using DyeTerminator™ Sequencing Protocol on an ABI 3100 DNA Analyser (Applied Biosystems, Foster City, CA).
In patients with initial distal leg weakness, muscle CT scans at the midcalf level showed fatty replacement in soleus and medial gastrocnemius muscles followed by anterior tibialis and peroneal group, and mild involvement of the hip adductors. In cases with proximal onset, muscle hypodensity was noted in the hip adductors, biceps femoris, semimembranosus and sartorius with no obvious changes in the calf muscles. Finally, in the patient with both proximal and distal initial muscle weakness, marked decrease of attenuation was observed in medial gastrocnemious, soleus, hip adductors and biceps femoris. In advanced illness, all muscles of the anterior and posterior compartments of the legs were completely replaced by fatty tissue, irrespective of the mode of presentation. The quadriceps muscles, especially rectus femoris and vastus lateralis, were relatively well preserved.