Patients with inherited muscle diseases can have several miscellaneous problems in their muscles, which can be both structural and metabolic. Depending on the specific disease multiple symptoms may be present. All the different diseases can affect the contractility of the muscles. Examples of inherited muscle diseases are congenital myopathies and RYR1-myopathy, afflicting the muscle fiber structure. They are the first subgroups of inherited muscle diseases to be investigated in this study. Congenital myopathies are hereditary and relatively non-progressive diseases. Hypotonia is the clinical characteristic of congenital myopathies and is often presented already in the neonatal period. Almost all patients have generalized muscle weakness and hypotonia. The various subtypes of congenital myopathy are a broad group of disorders defined by the predominance of particular and specific structural abnormalities shown in muscle biopsies. Based on genetic and morphological features, they can be divided into four main groups; one with central cores, one with central nuclei, one with minicores and one with nemaline bodies. RYR1-myopathy is caused by a mutation in the RYR-gene. The RYR1-protein is important in the making of RYR1-receptors and channels responsible for the transport of calcium atoms within muscle cells, particularly in muscle contractions. Patients typically present with limb weakness, decreased fetal movement and skeletal abnormalities. About 70% of patients with malignant hyperthermia have a mutation in the RYR1-gene. MRI findings often include involvement of different muscles in the thigh and the calf.
Patients with inherited muscle diseases can have several problems in their muscles, which can be both structural and metabolic. All the different diseases can affect the contractility of the muscles. The aim of the study is to investigate the relation between muscle strength and contractile cross sectional area (CCSA) in the thigh and calf in patients affected by inherited muscle diseases.