It is a congenital myopathy associated with proximal extremity weaknesses, external ophthalmoplegia, and eventual respiratory failure. In the neonatal subgroup, severe muscular hypotonia, delayed motor development, generalized muscle weakness, and lateral amyotrophy that may progress or remain stable are characteristics of this disorder. One of the subgroups in this medical condition is called “Central Core Diseases” and a close susceptibility to malignant hyperthermia has been suggested.
MmD; Multicore Myopathy with External Ophthalmoplegia; Minicore Myopathy with External Ophthalmoplegia; Multi-minicore Disease; Minicore myopathy; Multicore myopathy; Multiminicore myopathy; Multiminicore disease with external ophthalmoplegia.
This medical condition was originally reported in a family with two affected siblings and suggestive histopathological findings by AG Engel et al in 1971.
There are two subgroups that consist of:
Recessive Mutations in the Selenoprotein N (SEPN1) Gene: Probably rarer and result in skeletal muscle ryanodine receptor (RYR1) gene dysfunction;
Mutations in RYR1 Gene: Most common in congenital myopathies including central core disease (CCD), certain forms of centronuclear myopathy (CNM) and specific subgroups of MmD.
The exact incidence for this medical condition remains unknown. The prevalence is unknown. There are no more than 30 cases of this medical condition that have been reported in the literature. Epidemiological data are only available for the congenital myopathies as a group, but not for individual conditions. The incidence of all congenital myopathies is estimated at around 0.06/1,000 live births, or one-tenth of all cases of neuromuscular disorders. In Northern Ireland and Western Sweden, it is suggested that the frequency is approximately 3.5 to 5.0/100,000 in a general pediatric population.
It is believed inherited as an autosomal recessive pattern. There is also a possible autosomal dominant form that has been suggested.
Myopathy characterized by the presence of multiple, short, core lesions (known as minicores) in most muscle fibers as a result of sarcomere disorganization and mitochondria depletion. Four subgroups have been identified. RYR1 mutations were recently identified in the moderate form—the central core disease. The genes responsible for the three other forms remain unknown, but a mutation of the selenoprotein N gene is implicated.
The most prevalent phenotype is characterized by the predominance of axial muscle weakness that leads, in two-thirds of patients, to development of severe life-threatening respiratory insufficiency and scoliosis. The second group is the classic form with ophthalmoplegia, which occurs in only 10% of cases. The third group consists of the mild cases of central core disease. The fourth group is rare and probably consists of rigid spine dystrophy.
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