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Congenital Myopathy defines a large spectrum of congenital diseases that are usually present at birth. It is characterized by muscular weakness and/or hypotonia. Congenital myopathies are considered the number one neuromuscular disorders in the world today. The estimated prevalence is established as approximately 6 in 100,000 live births every year in the general population. Congenital myopathies are classified according to the type of muscle fibers and genetic variations. They consist of:
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Myopathies with inclusion bodies and abnormal protein accumulation: Characterized by cellular inclusion bodies and protein accumulation in sarcoplasm that leads to muscle dysfunctions, such as observed in nemaline myopathy (see below).
Myopathies with Core: Characterized by sharply-demarcated areas devoid of oxidative enzymes NADH, SDH, and COX in muscle fibers. It is seen in multicore myopathy and central core diseases.
Myopathies with central nuclei: Involves vesicles reaching the plasma membrane within the cellular components causing myoblast to fuse and creating severe dysfunctions in the formation of the skeletal muscles. Myopathies with central nuclei are seen in myotubular myopathy.
Myopathies with fiber size variations: Characterized by varying fiber size, such as congenital fiber type disproportion. It occurs when type 1 fibers, the slow twitch fibers involved in sustaining prolong activity, are smaller than type 2 fibers, the fast twitch fibers involved in quick activity.
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The conditions included under the term “congenital myopathy” vary greatly. They include numerous medical conditions that are defined by their structural anomaly. The term can also be used more broadly, to describe conditions present from birth. The subtypes include:
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Nemaline myopathy: Most common congenital myopathy. This medical condition was first described in 1963. Clinically, it is characterized by generalized muscle weakness, hypotonia and respiratory failure. It is inherited as an autosomal dominant and has also been seen as an autosomal recessive trait.
Myotubular myopathy (centronuclear myopathy): Characterized by inappropriate pain level for the type of exercise. Also, there is significant difficulty walking. Other features include young adulthood wheelchair bound, limited eye movements, peripheral nerve dysfunction, and intellectual disability. There are only 50 families currently affected and reported in the literature. It is believed caused by a mutation in the DNM2 gene. The disorder is inherited as an autosomal dominant. However, the most common form of inheritance is autosomal recessive as it pertains to a mutation in the B1N1 gene.
Central core disease or central core myopathy: Medical condition characterized by an onset of symptoms during infancy or early childhood presenting a nonprogressive mild proximal weakness that persists during the entire life of the affected child. It is of upmost importance for anesthesiologists as it is allelic to malignant hyperthermia. It is caused by a mutation in the RYR1 gene (same than MH). It was first described in 1956.
Congenital fiber type disproportion: Characterized by an onset of the disease within infancy, which manifests itself with muscle weakness, especially located in the shoulders, upper arms, thighs, and hips. This medical ...